Studies in the Physical Ecology
of the Noctuidae
So ee Fi hei el a “a a fh =
: q B ¢ enw \ f "5
: » # A 3
rT r= kt nr =
% i
A THESIS SUBMITTED TO, THE FACULTY OF THE GRADUATE
SCHOOL OF THE UNIVERSITY OF MINNESOTA
BY
WILLIAM CARMICHAEL COOK
IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE
DEGREE OF DOCTOR OF PHILOSOPHY
49.252
MINNEAPOLIS
CONTENTS
Page
IAEF OCU CEG Recah oye us trace cee er es Sree te eee ic ear ake ea RR apne tee 5)
Definitions Ofc terms sje Ve ide am eer nel a is ay We abi ery to 3
Literature eso Ayo EG i eek Oe eat cae tinier on re rena he Co eee ae «|
Littesrat Stidy pursued 4.4 vy Boteee aeete the we cen Roe ene nee eee ee 6
Meth ods etisedsJivc% rotecyet somata Caan tae Gee earn ae ene a, Seer 6
Comparative climatology of Minnesota and Montana. 3. ..7-.> a.2-. ee 7
General ecology of the Noctuidae of Minnesota and Montana... ..:....... 9
Larval habits, oc. «0 sce sacs ate eirad he. ele Oe eee Ree ec ee 10
Acdtilts habits cio obs. 5 iat. G teenies Bie cee aria oat en gate ea NI an 11
Physical-ecology .of ammatures Stages cre ust card eee ee eee 12
Laboratory studiéss.< sews t 2. oe dente tees ce ae ne ‘We
Soilmoisture “relations vou oa ach ler eens eras et ae en re 12
‘Léemperature: relations. senate er eee eee ee A Alig ae 15
Fieldt and ‘statistical sstindiese . spon. ter ns aes arenes reac 16
Conclusions 4... eet ee eee Fah esis Wi AL Oe: iE ae, ae En ee 29
Meteorologicalerelations ofsadult moths: sores 5 arene ote ea er eee 30
Methods ‘of-statisticalanalysisen 4 ngs eet ae tate eee 34
CoriclusSiGng Seo. AS Nn oie ee anal ose oe cee need 19h eee eR aa 36
Bibliography: So pclae. aikts oo ooo Seatac St een ae et 37
ILEVST RATIONS
Page
Plates ts Comparative sclimatolog yess ans ceee rere aes tre ee AY
Plate-1 ll Demperaturerelationes..- nce ne ee ee Renee Wi 17
Plate III. Meteorological relations of Cirphis untpuncta.....+. o..ti.....- 23
Plate 1V 2 Climatological srelations;0f.N Octuidae seam tes ees 24
Plate ,_V.=) Meteorological relations of sadulemoti= recente een ee 33
re ee + FeLt11.+2.2_e oO Ce
on
era Cee
STUDIES IN THE PHYSICAL ECOLOGY
OF THE NOCTUIDAE
3y W. C. Cook
INTRODUCTION
This paper gives the results of an attempt to determine the effects
of the various meteorological factors on the distribution, seasonal
abundance, and activity of certain species of the insect family
Noctuidae, which are commonly classed as cutworms and army worms.
As yet the studies include but few species, but the results so far
obtained seem of fundamental importance, and the methods used, altho
somewhat novel to entomologists, are applicable to the solution of
many similar economic problems.
DEFINITIONS OF TERMS
Physical ecology may be defined as the study of physical factors in
their relation to the ecology of a species. Such factors are light, heat,
and moisture as opposed to associational factors such as parasites, or
chemical factors such as food relations. The study of these physical —
factors under field conditions comes within the realm of meteorology,
and the factors themselves fall into two general classes, weather and
climate. Prof. J. Warren Smith (’20, p. 1)’ makes the following
comparison of these groups:
“Weather is the condition of the atmosphere at a definite time. It
includes all the phenomena of the air that surrounds us, such as pres-
sure, temperature, moisture, wind, and the like.
“Climate deals with the averages and the extremes of the weather
that prevail at any place. Thus it will be seen that weather relates to
time and climate to location.”
LITERATURE
Most of the previous work on insect forms has been confined to
laboratory experiments under controlled conditions or to the drawing
of general conclusions from a superficial study of field data, without
subjecting the data to any form of mathematical analysis. This is the
case in the early development of any branch of science, the qualitative
form preceding the quantitative. Our entire knowledge of quantita-
tive physical ecology may be said to consist of a few definite laws of
growth deduced from laboratory experiments, and a few broad
generalizations on the effects of climate on animal and plant distribu-
cited at the end of
1Datés in parentheses refer to titles in the list of literature
the paper.
4 1 BCANICALISUELETIN 212
tion and activity. Some of the more important of these deductions
are worthy of mention in connection with this specific problem.
Working under controlled laboratory conditions, Sanderson and
Peairs (713) determined that the effect of temperature upon insect
growth might be represented by a rectangular hyperbola of the
formula XY=A?’, A being a constant, called by them the thermal
constant, X being the temperature, and Y being the time of develop-
ment. By plotting X against || the plot becomes a straight line which
intersects the temperature axis at the point === (); Ol pOiit Ol ato
growth, which they called the developmental zero. The quantity :
they have termed the index of development, and it represents the part
of total growth accomplished in one day. In most cases in which this
method of plotting was used, it has been found that the relations out-
lined above hold true for the portion of the temperature range which
is approximated under field conditions, and that the developmental zero
found mathematically is a very close approximation to the point of
dormancy under field conditions.
W. D. Pierce (16) showed that the effect of temperature com-
bined with humidity was to change the developmental zero of Sander-
son to an elliptical curve whose foci were the optimum condition, and
that Sanderson’s curve of growth was a zone inside of this ellipse.
Any cross-section of this zone, parallel to the humidity axis, gave a
hyperbolic temperature curve, as before.
Studying the distributional data obtained by the United States
Biological Survey, C. H. Merriam (’98) formulated a general law of
animal and plant distribution, as follows (798, p. 54).
“Investigations conducted by the Biological Survey have shown that
the northward distribution of terrestrial animals and plants is governed
hy the sum of the positive or effective temperatures for the entire sea-
son of growth and reproduction, and that the southward distribution
ts governed by the mean temperature of a brief period during the
hottest part of the year.”
By the term “effective temperatures” is meant all temperatures
above 43° F, which was then regarded as a general developmental
zero.
Sanderson (’08) showed quite conclusively that the northward dis-
tribution of some insect species was limited, not by the sum of effec-
tive temperatures, but by the minimum winter temperature, and
recommended the inclusion of this factor in Merriam’s law.
A. D. Hopkins (718) has formulated an empirical bioclimatic law,
stating that in general, in temperate North America, the time of
occurrence of any given periodic event in life activity becomes later in
the spring and earlier in the fall as we progress northward, eastward,
ur
PHYSICAL ECOLOGY OF THE NOCTUIDAE
and upward. The general rate of change is four days for each degree
of latitude, each five degrees of longitude, and each four hundred feet
of altitude.
The bioclimatic law does not represent conditions on the Pacific
Coast, and there is a gradually decreasing error in its application until
the region well east of the Rocky Mountains is reached. As the
author of the law has stated, it is a purely empirical deduction from
held observations, and apparently the basis of the law is the gradual
change from marine to continental climate progressing from east to
west as we go inland. Possibly a restatement of the law, based upon
distance from the ocean rather than upon westward progression,
would give smaller errors in the western part of the range.
Aside from the general problem of the effects of climate upon
animal distribution, efforts have been made to connect certain climatic
conditions with specific insect outbreaks. No attempt will be made
here to include all the work done on this problem, but a few abstracts
will be given to show the general character of the work.
One of the early attempts in this direction was the hypothesis
advanced by Asa Fitch (’60) to account for army worm outbreaks. It
is quoted in full (’60, p. 121).
4 more briefly expressed, my view is this
and fel swamps multiplies this insect. And when it is thus multiplied,
a wet season and overflowed swamps drives it out from its lurking
place in flocks, alighting here and there over the country. But on
being thus rusticated, it finds our arable lands too dry for it and
immediately on maturing and getting its wings again, it flies back to
the swamps, whereby it happens that we see no more of It.”
This view was also supported by C. V. Riley (’70, ’76), and shows
that even in this early stage in the development of entomology, it was
recognized that climatic factors might explain insect outbreaks.
Charles G. Barrett (’82) gives notes on the distribution of various
Noctuid species in an English district following two types of winter
conditions, and concludes that the abundance or rarity of native
species is largely determined by climatic conditions. Four successive
mild winters made certain species, which were ordinarily common,
very rare, and other ordinarily rare species quite common. Following
these winters came three severe winters, after which the normal
balance was restored.
In considering the relation of precipitation to insect distribution,
Criddle (’17) cited the Rocky Mountain Locust as an example of an
insect which is increased greatly during dry seasons, and also states
that in Manitoba the Hessian Fly is checked by a drouth sufficient to
ripen the wheat prematurely. He shows that the combination of light
a dry season
6 TECHNICAL BULLETIN 12
snowfall and low winter temperature has been fatal to the Colorado
potato beetle in most parts of Manitoba, and considers that it will
probably never be a major pest in that region.
In the realm of plant ecology, especially in the study of the
economic crop plants, there is a rapidly increasing body of work upon
the mathematical study and analysis of climatic relations. J. Warren
Smith (’20) brings together the principal work. relating to the effects
of climate upon crops, using statistical methods for the more or less
exact definition of critical growth periods. In many cases it is now
possible to predict the amount of a given crop on a certain area if the
weather conditions during these critical periods are known. ‘This
work is very valuable and suggestive, and the methods used there have
been adopted in part in this paper.
DINEST OR SGD YSP UR SUED
This paper is based upon studies along three distinct but related
lines, laboratory experiments upon temperature and soil moisture
relations, attempts to correlate these results with the conditions sur-
rounding outbreaks of three species in the field, and a statistical
interpretation of data relative to the effects of weather conditions on
moth flight. The work was begun at University Farm, St. Paul, in
1919, in connection with cutworm investigations undertaken for the
Minnesota Agricultural Experiment Station, and carried through two
seasons, during which time all the original data relating to Minnesota
conditions were secured. During 1921 the work was carried on in
Montana in connection with investigations of the life history and con-
trol of the Pale Western cutworm (Porosagrotis orthogonia Morr.)
for the Montana Agricultural Experiment Station, and all the original
data relating to Montana conditions were obtained. The writer wishes
to acknowledge his indebtedness to the authorities of both stations for
the opportunity to study the problems, and for many courtesies
extended during the work; and especially to Dr. R. N. Chapman, of
the University of Minnesota, under whose direct supervision most of
the Minnesota work was done, and whose advice and assistance have
been invaluable. He also wishes to thank Mr. U. G. Purssell, Mr.
C. M. Ling, and Mr. W. T. Lathrop, Meteorologists of the United
States Weather Bureau at Minneapolis, Havre, and Helena, respec-
tively, for their co-operation in supplying meteorological data used in
these studies.
METHODS, USED
In a previous paper (Cook ’21), the author published the Minne-
sota data relative to the effects of weather upon moth flight, using the
method of partial correlation in their interpretation. This paper
PHYSICAL ECOLOGY OF THE NOCTUIDAE 7
extends this discussion, using similar methods in this part of the work
These methods are well explained in Yule (719) and Smith (’20). The
method of correlation depends upon the basic assumption that the
relation between the factors studied lies along a straight line, which is
approximately the case with the moth flight data, with the same
exception noted in the previous paper’ (’21, p. 53). Partial correlation
assumes a casual relationship between the factors correlated, which is
justified in the work on moth flight, but can not be readily assumed in
the work on the relation of climatic conditions to larval growth, so
that in this latter case, only total correlation is used. It was found,
upon plotting the points of the general climatic relations shown in
Plate IV, that these did not le along a straight line, so a curve was
fitted to them by the method of least squares (Leland ’21). Several
other somewhat simpler but less accurate methods may be found in
Lipka (’21), which is a valuable aid in this sort of work.
In any study of the relation of organisms to their environment, it
is necessary to develop some method of correlating laboratory experi-
ments with field observations. The laboratory experiment shows what
the organism will do in a certain controlled environment, while the
field observation shows what it does under constantly fluctuating con-
ditions. If we can reduce the field condition to some sort of an
expression representing the optimum condition and can determine the
optimum under controlled conditions, then we may say that the two
conditions are equivalent. Because of the wide fluctuations in field
conditions, it is necessary to treat the mean of a large series of
observations instead of using a single observation, and the only avail-
able method of determining field relations is that of statistics, which
has wide social and biometric applications. The accuracy of the result
varies as the square root of the number of observations, so that long
series of data yield more accurate results than short series.
COMPARATIVE CLIMATOLOGY OF MINNESOTA
AND MONTANA
The studies on which this paper is based were carried on under
two essentially different climatic conditions, and these differences are
best brought out by a comparison. It is difficult to compare two large
areas, so the two points where moth flight experiments were conducted
were selected as typical, and their climatic features compared.
St. Paul, Minn., is in latitude 44° 58’ N, longitude 93° 03’ W; and
Havre, Mont., in latitude 48° 34’ N, longitude 109° 40’ W. Both of
these general regions are in the Transition Zone of Merriam (’98), but
tS) TECHNICAL BULLETIN I2
are considered as separate faunae by Thompson-Seton (’09), who
places Minnesota chiefly in the West Alleghenian fauna and Montana
chiefly in the Campestrian fauna. Table I, the data for which were
secured from Henry (’06), shows the nature of the climatic dif-
ferences between the two regions, and Figure 1, Plate I, is a climo-
graph constructed from the data of Table I.
= TABLE I
CLIMATOLOGY OF HAVRE, MONT., AND ST. PAUL, MINN.
Temperature
Month Mean monthly Daily range’ | Humidity Total monthly
we FP" FL 301 Sa6t- Precipitation
Havre St. Paul Havre St. Paul Havre St) Paul Havirelest. ebaul
Degrees Degrees Degrees Degrees Percent Percent | Inches} Inches
January 3 12 19 18 76 76 0.8 1.0
February 14 16 21 7, Hd 76 0.5 0.6
March Di 29 21 18 70 68 0.6 1.6
April 44 48 24 20 44 54 1.0 25
May 53 60 25 20 45 51 2.1 B:3
June 61 66 24 19 43 56 2.9 4.4
July 68 74 | ot 35 54 2e1 3.6
August 66 72 29 20 34 | 55 1S 3.4
September 55 62 27 20 44 58 ileat SES)
October 44 50 24 18 56 62 0.6 2S
November 28 32 21 16 71 69 0.7 ily
December 22, 20 19 16 7S) 76 0.5 132
Meanannual 41 45 23 18 56 63 ade .-
Total anntial |) acres ood Stes ese teers cei I ieee eee Re eee ears | eae ay el Wn ee ne 1 oy 28.6
GENERAL CLIMATIC DATA
Temperature Havre Sits S22 yn | Havre St. Paul
Mean maximum, degrees.. 53 56 Average date
Mean minimum, degrees.. 30 36 last spring frost..... May 17 May 6
Absolute maximum,degrees| 108 104 firstetalletrosty ase elie ep Crs Octs5
Absolute minimum,degrees| —55 —41 Average length of
No. days above 90°...... 20 if growing season, days. 124 152
No. days below 32°...... 168 158 ;
The climograph is a diagram originally introduced by Ball (10)
and modified by several workers, of whom Varney (’20) is one of the
latest. The mean monthly figures for temperature and humidity are
plotted against each other, and the dots for the successive months are
connected by a line with arrowheads showing the direction of change
in the annual cycle. A recent contribution by Flanders (’22) gives
many variations in the use of the climograph for planting various pairs
of weather factors.
The summer humidity conditions are radically different in the two
regions, the period from April to September representing in Montana
a condition of dryness never reached in Minnesota. This dry sum-
mer condition practically eliminates the possibility of two-brooded
species, so that few such species occur in the plains region of
PHYSICAL ECOLOGY OF THE NOCTUIDAE 9
Montana. Another factor of considerable importance in the ecology
of the moths is the large diurnal temperature range in Montana, which
restricts flight to the late afternoon and early evening during a large
part of the summer season. Winter conditions are very similar in the
two regions, so that this factor should not operate to differentiate the
two faunae.
| LT TL abombaekrte dumborhen| | |
PA ahevworh
, toe pte Ss
=]
Fela tuve Fes rid hy
510% | 610%
Plate I. Comparative Climatology
Figure 1. A comparative climograph of the annual cycles at St. Paul,
Minn., and Havre, Mont.
GEN PR ise GOMGG Ore int NOC LULIDARAOER
MINNESOTA AND MONTANA
As would be expected from the radical climatic differences, the
Noctuid faunae of the two regions are essentially different, as 1s
brought out in Table II, which is a compilation from Hampson
('03-’09). The species listed as western or eastern are not confined to
Montana and Minnesota, but represent roughly semi-arid west and
humid east. In order to show the relations of these regions to the
generic centers of dispersal, the number of Palearctic species in each
genus is included. Roughly, that region showing the greatest number
of species is generally the center of dispersal (Folsom ’06, p. 383).
The predominating western genera are of western origin,
apparently, and none of their species is common to Europe and Amer-
ica, while the typical eastern genera are obviously of European origin.
In this connection it is interesting to note the comment of John B.
10) TECHNICAL BULLETIN 12
Smith (90, p. 11) with regard to the character of our American
Agrotid fauna:
“Tt is suggestive that so large a proportion of our species are from
the western part of our country, and that those species are mostly
referable to those genera in which the front is modified in some way
and the tibial armature heavy. In fact, the distinctive character of our
western fauna is shown in the very predominance, and sometimes
abnormal development, of tibial and clypeal armature.”
TABLE 11
NOCTUID DISTRIBUTION IN THE HOLARCTIC REALM
Number of nearctic species Number of
Eastern Western Common Palearctic Holarctic
Genus No. America |No. America to both species species
HUK OA Sara Sete he ae 25 163 10 84 0
Ghorizacrotisce eee 0 5 0 4 0
Porosacko bisa eee 1 1:2 1 0 0
Heltia es Ase eas atk. 7 11 1 3 0
POliae sie ee ee oe. 34 63 2 el 0
A OT OUI Hane cee seek ee 22 17 0 79 3
Cirphis iain we re ee ee 7 7 0 66 3
PATASLICH LICHEN NT eee TD 9 1 16 0
Arropenina ie ent sa ee & 3 1 1 0)
SICdemiat ye ein each eee oe 1 2) 1 9 0
Totals
Western 2roupis.. 2... 4. 67 254 14 161 0
Paster SLOuD es aan een 47 38 3 aie 6
Grandetotalsvereey er eens 114 292 17 332 6
The species of Euxoa, Chorizagrotis, and Porosagrotis are
regarded by Hampson as representing the highest development of the
Noctuid type, and this structural position is borne out by their ecology.
They differ from the eastern species in many important respects, in
all of which they are more highly specialized than the latter.
LARVAL HABITS
Cutworms may be grouped in three classes according to feeding
habits. Climbing cutworms climb plants, eating the foliage without
always destroying the main stem. Lycophotia margaritosa and Poro-
sagrotis vetusta belong to this class. (Slingerland.) The great
majority of the eastern species feed at or just above the surface of the
ground, and may be called surface cutworms. [Examples of this type
are Feltia ducens, Euxoa messoria, and E. tessellata. A third and
more recent type in point of development is the group of sub-surface
feeders, or subterranean cutworms. Among the comparatively few
species known to have this habit, is Porosagrotis orthogoma and, pos-
sibly, Sidemia devastator. P. orthogonia feeds entirely below the sur-
face, cutting off plants from one to two inches below the surface of
the soil, and moving from one to another underground, except under
*
PHYSICAL ECOLOGY OF THE NOCTUIDAE 11
abnormal conditions such as heavy rainfall. All the most abundant
Montana cutworms are either surface or subterranean feeders, with
several species suspected of the latter habit, altho this has not been
proved except in the case mentioned.
ADULT HABITS
In the habits of the adults as well as in those of the larvae, the
species of the two regions are quite different. In the first place, the
cutworm moths of the Montana group are very strong in flight. This
was well shown during the early summer of 1921, when thousands of
specimens of Chortzagrotis auxiliaris, the Western Army cutworm,
were captured in Minnesota, Iowa, and Kansas. This species breeds
normally in the plains region of Montana (Cooley, 716) and has never
been reported in large numbers east of that region. This means that
in 1921 the moths must have flown at least three hundred miles from
the place where they emerged.
Another peculiarity in the life history of C. ausxiliaris ee Agrotis
unicolor Walk. (Noctua clandestina Harris), as recorded by Strick-
land (16), is the habit of aestivation in the adult stage. The moths
emerge in June and aestivate for a period of at least three months
before maturation of the ovaries and oviposition. None of the com-
mon Minnesota species (with the possible exception of A. unicolor,
which also breeds in Minnesota) are known to have any similar habits.
This aestivation is apparently the method chosen by these species to
escape the intense heat and drought of July and August in Montana.
Very little is known concerning the oviposition habits of Noctuidae,
but all the eastern species whose habits are known lay their eggs
directly on green vegetation. This is definitely known for Agrotis
ypsilon, Feltia ducens, Polia lorea, Lycophotia margaritosa, and
Cirphis unipuncta. Those Western species whose habits are known,
on the other hand, lay their eggs either on trash on the surface of the
soil (C. auxiliaris, Strickland ’16), or in the surface layer of the soil.
(P. orthogonia, Parker, Strand, and Seamans, ’21). Several species
of Euxoa are suspected of similar habits, but have not been found
ovipositing as yet.
In reproductive capacity the Eastern species in general outrank the
Western, with some exceptions. Thus, it was found in Insectary work
at University Farm that L. margaritosa lays as many as 3000 eggs, an
average figure obtained from twenty-eight moths being 1497. Felita
annexa (Jones, 18), lays as many as 1300 eggs, an average for ten
females being 794. C. unipuncta has been captured with as many as
S00 eggs in the ovaries (Turner ’18), and probably lays many more in
12 TECHNICAL BULLETIN 12
the field. Among the Western species, P. orthogonia averaged 315
eggs each for five females (Parker, Strand, and Seamans, ’21), and
C. auxiliaris laid about 1000 eggs (Strickland ’16), which figures ‘are
the only ones available for Western species. It is evident that P.
orthogonia, the most highly developed cutworm ecologically, does not
need so high a reproductive capacity, as the eggs, being scattered in
small clusters through the soil, have a much larger chance of survival.
Another factor to be considered in connection with reproductive
capacity is the ability of the species to produce sudden and severe out-
breaks. A species with a high reproductive capacity can multiply very
rapidly, and a small number of moths surviving a hard winter can
quickly bring up the population to a destructive number. Such species
as C. unipuncta and C. auxiliaris and L. margaritosa can produce these
sudden severe outbreaks, as is evident from a superficial survey of the
general economic literature. On the other hand, P. orthogonia does
not suddenly appear in large numbers, but produces a gradually
increasing population in any given place until checked by climatic con-
ditions, when the cycle is recommenced.
PHY SICA TSE CO LG GYR© FS TIVEND Es Tee Teo leno bies
LABORATORY -SiUDiEs
In order to obtain some experimental evidence with regard to the
relations of the various stages of Noctuids to temperature and
numidity, laboratory experiments were carried on at University Farm,
St. Paul, during the winters of 1919-20 and 1920-21. It was the inten-
iion of the writer to rear as many species as possible under controlled
conditions, but L. margaritosa was the only species which was obtained
in large enough numbers for this work. As atmospheric humidity has
a very small influence on the insect during the larval stages, which are
spent in the surface layer of the soil, the moisture of the direct
environment, namely, soil moisture, was studied instead.
SOIL MOISTURE RELATIONS
The method used in determining the relations of L. margaritosa to
soil moisture were in general those of students of plant physiology,
being the rearing of the insect in a cage of soil whose known moisture
content was held approximately constant by the daily addition of suf-
ficient water to maintain a constant weight. Lantern globes covered
over the top with coarse muslin were placed over the soil in a pot hold-
ing about five pounds of soil. The original moisture content of the
soil was determined, sufficient water added to secure the required
moisture content, the weight of pot, soil, and cage taken and held
PHYSICAL ECOLOGY OF THE NOCTUIDAE 13
constant throughout the experiment. The freshly-laid eggs were
placed on the surface of the soil in the cage, and the insects reared to
the adult stage under the same constant moisture condition. A
thermograph was kept in close proximity to the cages to give a con-
tinuous record of air temperature, and all cages were kept close
together in the greenhouse under as uniform conditions as possible.
Two sets of experiments were performed, differing slightly in details,
and will be considered separately.
First experiment—1919-20.—In this experiment three soils were
used, a course sand with a maximum water capacity of about 32
per cent of dry weight; a rich leaf mold with a water capacity of
about 52 per cent of dry weight; and a mixture of equal parts of these
two, designated as loam, whose water capacity was about 41 per cent
of dry weight. Two cages were held at each moisture condition, of
which there were sixteen. The cages were examined each morning,
and the number and instar of the larvae present noted, so that the
figures given represent an average for the larvae of each two cages.
(LABibhe Lhe
MOISTURE RELATIONS OF LYCOPHOTIA MARGARITOSA
First EXPERIMENT, 1919-20
Water Content
per cent of No. off Egg |No. of} Larval | No. of Pupal No. of | Total Mor-
___————=*sS|:séeeggs:«=| period | larvae} period pupae period adults life tality
Dry Total
weight capacity
days days days days|Per cent
SAND} SERIES
5.0 eS 50 6.0 30 53.0* 0 Rees 0 59.0* 100.0
(es 23 17 8.0 14 36.5* 1* Sys 0 44.5% 100.0
10.0 32 24 7.0 13 9 Ie Ks 10) ay 0 29.3* 100.0
P25 39 18 8.0 12 59.6 2, DM A 2 89.5 96.4
15.0 47 60 7.0 52 58.1 7 22.3 3 92.3 95.0
20.0 63 ak 9.0 20 Spas 4 32.0 1 91.0 96.3
Series 196 TES 141 56.9 14 25.6 6 91.2 96.9
LOAM SERIES
5 14 30 7.0 2 8.0* 0 ee 0 TMS Obs 100.0
10 28 30 7.0 14 a fe 0 ane 0 54.1* 100.0
ily 42 30 6.0 23 5 SiG 4 23-2 4 $1.2 86.7
20 56 34 7.0 19 51.9 9 23.0 8 85.1 76.2
25 70 28 9.0 14 53.8 4 32.0 2 89.0 92.9
35 98 36 9.0 6 Sar 2 22.0 1 82.0 88.9
Series 191 PS 78 5202 19 24.3 LS 84.4 92.1
LEAFMOLD SERIES
10 19 pH | 7.0 20 56.5 17 bet 0) 63.5 100.0
20 38 28 8.0 22 50.6 1 2520) 1 92.0 88.9
30 Oy, 26 8.0 j WP 33.0 + 0 Tear: 0 39.0+! 100.0
40 | 76 Lan 8.0 10 48.0 4 23.6 3 80.0 82.4 |
Series | 98 1.7 54 48 3 6 23.9 4 83 0 << 95.9
*insects apparently died from lack of moisture before emerging as adults.
+Larvae in this cage killed by a fungous disease.
Considering both duration of stages and mortality, the loam was
the most favorable soil for growth. The minimum water requirement
of the species seems to be about 35 per cent of the total capacity on
each soil, and the optimum is above 50 per cent. There seems to be
14 TECHNICAL BULLETIN a2
no upper limit, altho probably a very wet soil is more favorable to the
development of fungi in the field, thus reducing the numbers of
insects.
Second experiment—1920-21.—The second set of experiments
was run as a check on the first, and was conducted in the same
greenhouse, under the same general conditions. Only one soil, a loam
mixture with a water capacity of 32 per cent, was used, and five cages
were run at each of six moisture conditions. In addition to the
thermograph as in the first experiment, readings were taken each
morning of the temperature of the surface soil in each cage, from
which the departure of that temperature from that of the thermograph
was computed and the actual temperature condition in the cage deter-
mined. Records were kept only of dates of hatching of eggs and
emergence of adults, together with the number of adults emerging,
from which the mortality percentage is calculated. The results of this
experiment are given in Table IV.
TABLE IV
MOISTURE RELATIONS OF LYCOPHOTIA MARGARITOSA
SECOND EXPERIMENT, 1920-21
Water content Larval
Per cent of and
pupal
Dry Total No. of Egg period No. of Total Mor-
weight capacity eggs period adults life tality
days days days Per cent
5 15 128 7 59.4 15 66.4 88.3
10 31 108 TD 68.5 13 76.0 87.9
BS) 47 80 Ths oe 11 82.6 86.2
20 62 99 8.5 76.6 25 85.1 74.8
25 78 85 9.0 83.6 12 92.6 85.9
30 94 90 9.0 78.6 21 87.6 76.7
The minimum moisture requirement is not so evident in this
experiment as in the first, but there is a definite optimum moisture of
about sixty per cent of capacity. In order to show the general trend
of both experiments, the data of Table III are combined with those of
Table IV to form Table V, in which the various moisture contents are
erouped into four general classes.
TABLE V
MOISTURE RELATIONS OF LYCOPHOTIA MARGARITOSA
Water
per cent cf No. of No. of Total Mortality
total capacity eggs adults life
Days Per cent
OktouesS 314 28 71.0 93.2
SO6\toO) 50 222 21 84.8 90.5
S1stoOr OS 183 34 85.3 81.4
66 to 100 256 39 88.5 84.8
PHYSICAL ECOLOGY OF THE NOCTUIDAE 15
The general conclusion to be drawn from these experiments is that
the Variegated cutworm has a definite moisture requirement, both
optimum and limiting, and that the optimum condition is about sixty
per cent of the total water capacity of the soil.
TEMPERATURE RELATIONS
Experiments were planned for the rearing of all stages of
L. margaritosa under controlled conditions of temperature, but it was
found that any obtainable constant temperature was too high for the
larval and later stages. The mortality was 100 per cent at all temper-
atures above 23° C., and only a single adult was secured at this
temperature. Experiments on the hatching of the eggs were more
successful. Table VI shows the results obtained from the exposure of
twenty-four masses of 50 to 400 eggs each to three different constant
temperatures. Four of the masses exposed to 30° C. failed to hatch,
and only a portion of the eggs in the other six masses hatched, show-
ing that this temperature approaches the upper limit of growth. The
figures for duration of egg period are weighted according to the num-
ber of individual eggs in the experiment. The figures in the columns
headed “Index of development” and “Thermal constant” are derived
as explained in the introduction in the discussion of the work of
Sanderson and Peairs (’13).
TABLE VI
TEMPERATURE RELATIONS OF LYCOPHOTIA MARGARITOSA
EGG STAGE
Temperature (C) Duration
1/(6) (2) x (6)
No. of Index of Thermal
Observed Effective masses Max. Min. Mean development constant
(1) (2) (3) (4) (S) (6) (7) (8)
Degrees Degrees Days Days Days
23 14.2 10 55 5.0 ae .192 73.84
27 18.2 4 4.0 4.0 4.0 .250 72.80
30 yale. 10 4.5 4.0 4.1 .244 86.92
In the second series of moisture experiments, daily readings were
taken of the temperature of the surface soil of each cage, from which
the actual cage temperature was computed. In Table VII are given
these temperature figures for the egg stage, together with the data on
duration of the egg period and computations of the index of develop-
ment and thermal constant on the basis of effective temperatures, as
in Table VI.
The results of both these experiments are plotted on Plate II, the
points for the two series being distinguished by the use of two
symbols. The agreement of the two sets is more than accidentally
16 TECANICGAT BE Leer ene
close, and we must conclude that moisture in itself has little influence
on the egg stage, except as it acts indirectly, by reducing temperature.
Figure 1, Plate II, shows the temperature hyperbola: drawn through all
the points, and Figure 2 shows the reciprocal line.
TABLE VII
TEMPERATURE RELATIONS OF THE EGG STAGE OF LYCOPHOTIA MARGARITOSA
UNDER CONTROLLED MOISTURE CONDITIONS
Water f Temperature (C)
per cent of
total No. of Egg Mean, Mean, Index of Thermal
capacity eggs period air cage development constant
Degrees Degrees
15 189 7.0 20 19.88 143 77.56
31 157 tas 20 18.99 AUST) 76.43
47 163 ths 20 18.26 .133 70.95
62 156 8.5 20 1 fe OS 118 70.98
78 85 9.0 20 16.44 ake 68.76
94 90 9.0 20 16.52 “fila 69.48
PIE UL DSANDES PATI S IGA es LUD
Very early in the course of these studies, in considering the rela-
tions of L. margaritosa to temperature and soil moisture, it became
quite evident that a knowledge of these optimum and limiting condi-
tions should be of great value in a study of the relations of meteoro-
logical factors to insect outbreaks. For example, knowing definitely
that the optimum soil moisture condition for this species is about 60
per cent of the total moisture capacity of any soil, would it not be a
logical step to assume that field conditions during a destructive out-
break must at least approach this condition? If this assumption is
correct, and the writer believes it to be, then, working back from this
hypothesis, the weather data, in terms of temperature and precipita-
tion, for the infested region during the period of the outbreak, must
represent this optimum. This, then, is the first problem. Is there any
definite indication of an approximately constant moisture condition in
the field, as expressed in the temperature and precipitation records,
and, if so, in which parts of the life history of the insect is this relation
most pronounced? Further, if possible, it is desirable to analyze the
weather data for the period covered by the destructive generation of
the insect and by the preceding winter generation, that is, for a period
extending at least a year previous to the outbreak, comparing condi-
tions in all months, in order to obtain indications of any relationships
which might aid in the climatological interpretation of the outbreak.
As it is necessary to deal with a large body of data in order to
obtain trustworthy results, it is evident that some method of analysis,
preferably some well-known standard method, must be used. For this
work the method of correlation, as developed by the writers referred
to in the introduction, is well adapted. The meteorological relations of
PHYSICAL ECOLOGY OF THE NOCTUIDAE 17
C. unipuncta in Minnesota have been quite carefully analyzed by this
method, and some of the more general relations of L. margaritosa and
P. orthogonia, altho the work done on these last two species is of a
preliminary nature, introduced in this paper for purposes of com-
parison.
N
ies PHOTIA| MARGARITOSA
po || eas =
LYCOPHOTIR TOSA 4
4 S) ariable TemptraTure,
Constant Mo:sfure
Jdo000 10 ahs f i oe :
Plate IJ. Temperature Relations
are
Pere
a
°
y Y tb q i
®
a
hy q
st
q
aH
D
>
5 b
)
K>
Figure 2. Hyperbolic temperature-growth curve for the egg stage of
Lycophotia margaritosa,
Figure 3. Reciprocal growth curve for the egg stage of Lycophotia mar-
garttosa,
18 TECHNICAL BULLETIN 12
METEOROLOGICAL RELATIONS OF CIRPHIS UNIPUNCTA
Since 1895 there have been five major outbreaks of the army worm
in Minnesota, which form the basis of this study. The general method
of attack consisted in determining first the distribution of the insect in
each outbreak, plotting the area roughly on a map, selecting all the
United States Weather Bureau stations inside this area, and assembling
the weather data for each station for the entire year preceding the
outbreak. Out of about seventy-five station records so secured,
twenty-one points were selected which had been in the area of destruc-
tive abundance for at least two of the five outbreaks, and their records
were assembled for the entire period, 1895-1920. As some of the
records were not complete for the entire year preceding an outbreak,
those incomplete records were eliminated, leaving a series of thirty-five
records, which were finally used as the basis of the statistical study.
This elimination secured a set of records from a single region, each
one represented more than once in the series, and all of them in
regions more than normally liable to army worm attacks. A description
of the area covered by each outbreak, the sources of information con-
cerning each, and a list of the stations used for each in the statistical
work follows.
1. 1896.
PHYSICAL ECOLOGY OF THE NOCTUIDAE 19
sonally investigated by the writer. Selected stations were Albert Lea,
Bird Island, Fairmont, Farmington, Grand Meadow, Luverne, Lynd,
Montevideo, New Ulm, Redwood Falls, St. Peter, Winona, Worthing-
ton, and Zumbrota.
5. 1920. A locally severe outbreak occurred over an area embrac-
ing portions of the counties of Rock, Pipestone, Murray, Cottonwood,
Lyon, and Redwood. The stations chosen were Bird Island, Luverne,
Lynd, and Montevideo.
Complete data for these stations may be found in the files of the
“Climatological Data, Minnesota Section,’ of the United States
Weather Bureau.
Having assembled these data, the next step is the search for some
methods of interpretation which will bring out the presence of a given
moisture condition such as was outlined above. A consideration of
the relationship between temperature, precipitation, and soil moisture
makes it evident that, considering the variation in the evaporating
power of the air at different temperatures, a heavy precipitation at a
high temperature would produce the same moisture condition in the
soil as a lighter rainfall at a lower temperature. That is, for example,
the moisture at 70 degrees F. and four inches precipitation would
probably be equivalent to that at 60 degrees F. and three inches rain-
fall. In other words, if we plot the temperature and precipitation
figures for the thirty-five stations on a dot chart, whose ordinate is
temperature and whose abcissa is precipitation, placing a dot at the
intersection of the axes representing the condition at each station, a
positive correlation between temperature and precipitation would rep-
resent the presence of an approximately constant moisture condition
at all the stations. The closer the relationship, and the nearer the dots
approach a straight line, the higher the value of the coefficient of cor-
relation, ‘‘r,” and the more critical this relationship in the economy of
the species.
A series of dot charts, constructed as outlined above, were prepared
for the conditions in each month of the year preceding an army worm
outbreak, each chart containing the thirty-five points representing the
selected stations. The correlation coefficient, “r” was calculated for
each chart, together with its “probable error.” The significance of ‘“‘r”’
is related to its probable error, a value less than three times the prob-
able error being of little significance, and one of more than six times
the probable error indicating a very critical relationship. In order to
determine whether these correlations were entirely due to the condi-
tions in years preceding army worm outbreaks, a second series of
charts was constructed, one for each month, on which the temperature
20 TECHNICAL BULLETIN 12
and precipitation for the twenty-one stations for the entire period of
twenty-five years were plotted. The difference between the correla-
tions in the latter set and those in the former set indicated the true
relationship of these conditions to army worm outbreaks. Both sets
of coefficients and probable errors are given in Table VIII. Those
months in which the value of “r’’ was near to six times its probable
error, and in which it varies greatly in the months preceding army
worm outbreaks from the value for the same month in the whole
period, are regarded as critical, and the month and value are repeated
in the fourth column.
TABLE VIII
CORRELATIONS OF TEMPERATURE WITH PRECIPITATION
35 Selected stations Significant
21 Stations for period correlation
Month entire period preceding or
1895-1920 army worm critical
outbreak period
ATP US tae eee ae +.129 +.031 —.007 +.113
SEDtEMDEeH aes eee +.038 +.033 +.421 +.093 +.421 September
Octobencne: seers — .064+.033 +.571+.077 +.571 October
INOVeMm Deiaceeee ae +.029 + .033 +.481 +.088 +.481 November
Decemberns ware +.017 +.033 Ss eee Se 2
anita tyep eee eet —.251 +.031 —.227 +.108
Hebatianyvaceacee oe +.319 +.030 +.242 +.107
Marcha arate —.390 +.028 —.416 +.094
Aprites tacts caceuct +-.012 =.033 —.318 +.102
Ma). cae Not ese +.096 + .033 +.548 +.079 +.548 May
Jina hater —.005 +.033 +.122 +.110
July Ss eet eee —.169 +.032 +.159 +.110
Analyzing the data in this manner shows that without any reason-
able doubt, there is present some definite, practically constant moisture
condition during the period preceding the outbreak, and that this cond1-
tion is most marked in the months of September, October, November,
and May, or during the larval life of the overwintering generation.
The correlations in the winter months are fairly high, but correspond
closely to those for the twenty-five year series, and hence are not
necessarily related to army worm outbreaks.
The next logical step would be to ascertain whether this moisture
condition is approximately equivalent in the various critical months,
but we will postpone this consideration until some other relationships
are studied. Let us next study the relations between successive
months, for the purpose of determining the presence of any seasonal
succession which is of importance. A consideration of the problem
will show that a negative correlation between temperature in two suc-
cessive months shows the presence of a necessary constant temperature
sum for those two months. That is, if a warm September is followed
always by a cold October, and a cold September by a warm October,
the sum of temperature for the two months will tend to remain con-
stant, and it remains for us to determine the significance of this
thermal constant in the economy of the army worm,
PHYSICAL ECOLOGY OF THE NOCTUIDAE 21
In order to test the presence of any such relationships, dot charts
and correlations were made by combining the temperature of each
month with that following, and with various other months where there
seemed to be any indication of a critical relationship. The same
procedure was followed with the precipitation data, and the more
significant of these correlations are given in Tables IX and X.
TABLE IX
TEMPERATURE RELATIONS BETWEEN SUCCESSIVE MONTHS
PRECEDING ARMY WORM OUTBREAKS
ers YT
September October November December January June July
September —.924 —.723 —.665 —.745 —.619 —.718
October +.796 +.781 +.884 +.785 +.770
November +.557 +.760 +.571
December +.928 +.378
January +.567
June +.788
July
TABLE X
PRECIPITATION RELATIONS BETWEEN SUCCESSIVE MONTHS
PRECEDING ARMY WORM OUTBREAKS
September October November December January June July
September —.364 —.170 —.254 —.361
October +.429 + .323 +.556
November
December
January
June +.607
July
Altho no general correlations were made, as in the case of the first
set of computations, it seems probable that these correlations given
here are all significant, especially those between successive months.
Vhe most interesting relationships are found in the temperature cond1-
tions in the fall and early winter months. Considering first, September,
October, and November, as they are the months in which the young
larva prepares for hibernation, it is apparent that there is a very high
correlaticn indicating the existence of a constant sum of temperature
for those three months. If September is warm, October and Novem-
ber are cold, and if September is cold, October and November are
warm. In order to test for the presence of this thermal constant, the
mean temperature for October and November was computed and cor-
related with the September temperature, which gave a value of —.77]
for “r.” Then the mean temperature for the three months was com-
puted for each station, and found to be 46.92, ranging from 43.6 to
49.7 F., with a standard deviation of 1.44 degrees. The standard
deyiations of the monthly temperatures of which this sum was com-
posed were 3.70, 3.47, and 3.56 degrees, respectively.
22 TECHNIGAL“BULEET INI
The significance of this thermal constant in the economy of the
insect evidently is in enabling the insect to reach a certain stage in
which it is best able to hibernate. Knight (’16) has shown that this
species can not hibernate in New York in the pupal stage, and evidently
the range in Minnesota is even narrower, probably being restricted to
two or three certain larval instars.
Another interesting temperature relationship is that between Sep-
tember and December and January, considered together. The relation-
ship is even higher when October is substituted for September. This
shows a very interesting balance between fall and winter conditions.
If September is warm, the young larva grows quite rapidly, but its
growth is checked by the cold weather in October and November, and
this gradual “hardening” process enables it to withstand low tempera-
tures in the early winter. On the other hand, if September is cold,
the slow growth is accelerated during the warm October and November
which follow, and the larva does not have the gradual hardening period
found in the former case, and is evidently unable to withstand such
cold weather in the early winter. These relationships are evidently
vital to the insect, and a more complete analysis of these and others
of lesser importance would probably enable us to predict the occur-
rence of army worms in any given locality by a study of the weather
data for the previous year.
On Plate III are shown a few of these dot charts for the correla-
tions in the fall and early winter months. The relationships are very
close for this class of data, and their importance should not be under-
estimated. Notice particularly the high correlations between tempera-
tures of successive periods, which are almost perfect in one case and
of high value in the others.
Now, returning to the consideration of the question raised earlier
in the paper as to the equivalence of the moisture conditions in the
various months, we will study that point more intensively. First, it
will be of value in visualizing the situation to show graphically how
the condition in each of these months departs from the average of the
region for twenty-five years. This is shown in Figure 4, Plate III.
The heavy central axes represent the normal condition, and departures
are measured from these in degrees F. and inches of rainfall. A circle
represents the position of each month with regard to normal condi-
tions. Six of the months are in the “warm, wet” quadrant, three in
the “warm, dry” quadrant, and three in the “cool, dry” quadrant.
None of them are in the “cool, wet” quadrant, a condition probably
favorable to fungous parasites. The winter months are all warm and
none of them very wet, indicating that a warm winter, with light snow-
PHYSICAL ECOLOGY OF THE NOCTUIDAE 23
fall, and presumably frequent freezing and thawing periods, is favor-
able to this species. This is also the case with the Pale Western
cutworm, to be noted later.
Ee
62-1150 -/100" - 0 {50°
(Wart, Dav)
°
Tempera ture| yn in Sthemb r on
cab ee ee ice ed ea
fean Te Real nae -jan —
ae 2
e .
re ene
peray
Ttkbera
AA pera lu
Cie aioe ty Dacembertand Japuary
CPT PET Aare s: Pr mig! trim orm °
ODE aL “~ pias LA \
‘neceding Army Worm
Outbreaks be es
1 J55° p Ae ached
Ary Whe Osprey
Pale es ao
Figak 8
etiSeplember Telmpera
A
fe
aTure >
S a
ae
S :
J
AN
Sa
3
2
x3
S
J
Plate III. Meteorological Relations of Cirphis unipuncta
Figure 4. Departures of monthly mean conditions from their respective
normals during the period preceding outbreaks of Cirphis unipuncta.
Figures 5, 6, 7, 8, 9. Correlations between the weather factors in the period
preceding army worm outbreaks.
5. September temperature and precipitation
October temperature and precipitation
September temperature and October temperature
September temperature and mean October-November temperature
Oo OND
October temperature and mean December-January temperature
24 TECHNIGCAL*BULIEETIN 12
== =
Argure elo be Army Worm Figure Lt The Vahega tea Caran
A/s\unt c/a Hd» | Lycophotia |margarfesa faw.
us |
‘ |
|
— Fred — Mecipi tation (vy) 1
#2 4: A p— bia ¢
ARS FW
Plate IV. net alone Relations of Rreeeidee
Figure 10. Moisture curve of Cirphis unipuncta
Figure 11. Moisture curve of Lycophotia margaritosa
Figure 12. Moisture curve of Porosagrotis orthogonia
Figure 13. The three curves combined, to show comparative conditions
and general distribution.
In the early part of this study, it was brought out that a positive
correlation between temperature and precipitation in any one month
indicated the existence of a nearly constant moisture condition. This
line would be approximately straight in considering the range of tem-
perature in any one month, but would probably be a curve when the
wide range of annual conditions is considered. As the amount of
*
_
eo
PHYSICAL ECOLOGY OF TAE NOCTUIDAE 25
moisture in the soil is a function of the evaporation of the air as well
as of temperature and precipitation, this curve should be of the same
general type as the curve which shows the amount of water vapor the
air can evaporate at any given temperature, in other words, the vapor
pressure curve of water. The formula for this, as given by physical
chemists, is approximately
log P, La5W Cie 15)
2.3025 — =
log P, 1.99 lad
We are not primarily interested in the various constants of this
curve, P representing vapor pressure; T, temperature, and W the
latent heat of vaporization, but we will note that it is logarithmic in
nature, and hence, if the temperature and precipitation points for the
various months are plotted on a graph, they should be capable of rep-
resentation by a similar logarithmic curve. Such a graph is shown in
Figure 10, Plate IV, and a curve computed to fit the points, whose
formula is given in the figure. The writer wishes to emphasize the
point that the selection of that particular formula was the result of
more or less guesswork, altho the constants are computed by least
square methods, and are accurate for that type of curve. It is possible
that future work will show that some other form of exponential curve
will express the moisture relations of the army worm more accurately.
However, the curve is semi-logarithmic, and a plot of the points on
semi-log paper shows them to fall in the neighborhood of a straight
line, which justifies the assumption of that type of formula.
To summarize the results of the analysis of the meteorological rela-
tions of Cirphis unipuncta, we may state the following conclusions :
1. The army worm evidently has a definite optimum moisture
requirement, as shown by the various correlations, which can be
expressed in terms of temperature and precipitation by the logarithmic
formula
log Y = 9.85188 — 10 +- .00999 X
in which X represents temperature and Y precipitation. Substitution
of given values of X in the equation give the corresponding log Y,
from which Y may be found. This equation represents the general
optimum condition, and any place whose annual conditions approach
this curve lies within the normal range of the species, and is liable to
infestation whenever the particular requirements outlined below are
satisfied.
2. In Minnesota, where hibernation takes place in the larval stage,
the sum of temperatures during September, October, and November
must approach 3 x 46.92° F.
26 THECANICAL BULLEEIN IZ
In addition, the temperature for the two months of December and
January taken together must bear the relation to that of October
expressed by the equation
Dec. temp. + Jan. temp. = 3.35 Oct. temp. — 120.4°
which equation is derived from the correlation in Figure 9, Plate IIT.
The above are the most important particular requirements which must
be fulfilled in Minnesota before an army worm outbreak occurs.
There are probably other minor conditions which combine with these,
but which are not so vital. The relation between temperature and
precipitation must, at least in September, October, November, and
May, approach the general condition outlined above.
METEOROLOGICAL RELATIONS OF LYCOPHOTIA MARGARITOSA
Unfortunately for this study, the only outbreak of this species in
Minnesota concerning which we have definite information available
was in 1919, in association with C. unipuncta, as was mentioned above.
With only this single outbreak as a basis, it seemed futile to attempt
much statistical work, as the results obtained would be of but slight
value. However, a comparative study of the weather data for this
outbreak and that for the other four army worm outbreaks should
yield some evidence as to the points of difference which made possible
the extreme abundance of L. margaritosa. Accordingly, the stations
listed for 1919 were separated from the rest of the data, and their
means computed. These figures, together with those for the Pale
Western cutworm, will be found in Table XI.
These means were then plotted in a manner similar to that used
with the mean figures for the army worm outbreaks, and a similar
exponential curve plotted to fit them, whose equation is
Log ‘Y == 0.03695: + .00845'X (Plate 1V,*Fig. 11)
This curve differs chiefly from the army worm curve in the size of
the constant term, indicating a larger basic amount of rainfall, and
showing that the Variegated cutworm prefers conditions more moist
than the army worm.
Knowing from laboratory experiments that the optimum moisture
condition for this species is about 60 per cent of total water capacity,
we can conclude that this curve represents an approximation to this
condition, and hence that the army worm curve, which represents a
slightly lesser amount of precipitation for any given temperature,
indicates the optimum for that species to be slightly lower, probably
in the neighborhood of 45 to 50 per cent of total capacity. The writer
has been unable as vet to confirm this fact experimentally, and it would
be a matter of considerable interest and value to do so.
PHYSICAL ECOLOGY OF THE NOCTUIDAE 27
Because the data are so meager, it is impossible to draw any con-
clusions with regard to any necessary succession of seasonal conditions,
as was done in the case of the army worm, so this part of the study is
incomplete.
METEOROLOGICAL RELATIONS OF POROSAGROTIS ORTHOGONIA
The two species whose climatic relations we have been considering -
are both normal inhabitants of the humid region of Minnesota, and
their moisture requirements are those natural to species of this region.
We will now consider these relations of Porosagrotis orthogonia, a
species whose habitat is a region with a normal rainfall of about four-
teen inches per annum, as compared to twenty-eight in Minnesota. It
is apparent that the moisture requirement of such a species must be
very much lower than those of the former two species, but it is not at
once apparent just how much lower it should be.
The Pale Western cutworm is a species which has very recently
become of great importance in many parts of Montana. It was first
noted in large numbers in 1915, and has since been rapidly increasing.
For a sketch of its distributional history, the reader is referred to
Parker, Strand, and Seamans (’21). The chief point of interest in
connection with its rapid increase is the fact that the last five years
(1917-21) have been a period of almost unprecedented drouth over
the infested regions, which has evidently been an important factor in
the ecology of the species. From distributional data on file at the
Entomology Department, Montana State College, maps were con-
structed as in the case of the army worm, and United States Weather
Bureau stations were selected as representative of conditions in the
infested regions. As this study is still in the early stages, the distribu-
tion and list of stations will not be published. |
Two points noted at the beginning of the study are of interest,
and will be mentioned. Tirst, a very superficial study of these distri-
butional maps in connection with maps showing the annual distribution
of precipitation for the period made it very evident that the greatest
amount of damage in any year fell within the area of the state receiv-
ing less than twelve inches of rainfall. This shows beyond a doubt
the semi-arid character of the optimum condition. Second, a plotting
of the monthly means for a period of about a year preceding outbreaks,
obtained in each case by the averaging of about forty points, gave the
distribution curve shown in Figure 12, Plate [V. Computing the
constants for this curve by the method of least squares gave the equa-
tion for this species as
Log Y = 9.48837 — 10 + .01158 X
28 TECHNICAL BULLETIN 12
Thus this curve, of a similar formula to the other two, varies in the
size of the constant term, and also in the greater value of the X term,
indicating a greater curvature than in the other cases. An inspection
of this curve as plotted shows the much smaller amounts of rainfali
necessary to produce the optimum for this species.
Another relation, on which very little work has been done other
than a preliminary examination of the data, is the relation to winter
conditions. Such an examination showed that winter conditions in
years and places preceding outbreaks were warmer than normal, and
drier than normal. Thus, this species, like the army worm, can with-
stand a considerable amount of freezing and thawing better than
steady cold weather with a heavy snow blanket.
COMPARATIVE CLIMATOLOGY
Now that the general climatic relations of these three species have
been outlined, it is of interest to compare these conditions with each
other and with other places, to show the significance of these relations
in the consideration of general distribution. Table XI gives the com-
parative conditions in the months preceding outbreaks of the three
species studied.
TABLE XI
COMPARATIVE CLIMATOLOGY
Month Porosagrotis Cir phis Lycophotia
preceding orthogonia unipuncta mar garitosa
Outbrea < p> 4
Temp. Precip. Temp. Precip. Temp. Precip.
Degrees Inches Degrees Inch s Degrees Inches
AS Shee ne eae 66.5 jn en Rae er tare Mies ie eee pe CRI uP Pac Beee Mee! so ABO) Ole ere
September....... Oat faa 59.4 Des) ya) 1.6
Octoberst aaa 41.4 es 47.0 1.8 51.0 SD,
INoOvem bGines see 28.6 0.6 34.1 2.6 36.9 re,
December 18.7 0.6 20.1 ial pli hay p 1.6
ania tyre oil sal 0.5 17.6 0.7 ZS22 0.5
Rebriaty. 4 ese Del 0.5 15.8 ee es Das
Nacht seen DERG 0.5 33.0) Absit 31.7 iba?
PNG OVRUNS ee a 41.4 ee 46.8 Sia: 45.4 3.8
INTaNy ieee eel rome Lyrey CA 56.6 2.6 56.9 2.0
Junction ae 59.4 2.0 68.3 Sys) 69.6 6.9
Julyee sss Soak Aa ee te oe eee ree TAS on 74.3 4.6
Totaliprecipitation!| esse ere TOs Sige i pee es vhtes cer 25 Age Vl ea eer at 30.2
This table shows conclusively the wide variation in the moisture
requirements of the three species, a fact which is shown graphically -
in Figure 13, Plate IV, on which all three of the curves are drawn in
their relations to each other.
lf these lines really represent the moisture requirements of these
species, any location in which one of them is normally found should
approach the moisture conditions indicated by the particular line. In
order to test this out, three points were chosen, one of which is within
range of the Pale Western cutworm, one in the range of the army
%,
ta
PHYSICAL ECOLOGY OF THE NOCTUIDAE 29
worm, and presumably, of the Variegated cutworm, and one of which
is outside of the range of the army worm, but possibly, under excep-
tional conditions in the range of the Variegated cutworm. ‘The three
points chosen were Glasgow, Mont.; Ithaca, N. Y.; and Jacksonville,
Fla. The data for their mean monthly temperatures and precipita-
tions were obtained from Henry (’06), and plotted on Figure 13 in
their proper relation to the three curves. The lines drawn connecting
the outside points of each station are of no especial significance, but
are merely introduced to bring out the general conditions at each point
more clearly. In the cases of Glasgow and Ithaca, the points are in
very close relation to the respective cutworm curves, showing that they
normally approach the necessary moisture condition. The condition at
Ithaca is of special interest when considered in connection with the
theory of Fitch (°60) which was evolved from a study of New York
conditions. Ithaca is normally slightly to the “wet” side of the army
worm curve, which accounts for the occurrence of army worms there
following dry seasons, as Fitch has indicated.
Jacksonville is not only at a considerable distance from either of
the curves for army worm and Variegated cutworm, but the major
axis of the polygon lies at a considerable angle to these curves. Tlius
it would not only take a wide variation in conditions to bring about an
army worm outbreak there, but this variation would have to be such
as would twist the axis of the distribution through a considerable
angle, a condition which practically excludes the possibility of exten-
sive outbreaks in that region.
It is hardly conceivable that either of the last two places would
ever become dry enough to be infested by the Pale Western cutworm,
or that Glasgow would ever be wet enough to be infested by the
army worm.
CONCLUSIONS
We may summarize the results of the studies on the relations of
meteorological conditions to outbreaks of these three Noctuid species
in the following statements.
1. Each of these species has a definite optimum and lin«ting soil
moisture requirement, which has been ascertained directly by labora-
tory experiments in the case of Lycophotia margari.osa, and indirectly,
by a study of conditions surrounding outbreaks in the case of the
other two species. This moisture requirement is capable of mathe-
matical expression in the form of an equation similar to that express-
ing the relation of vapor pressure of water to temperature, giving
directly the optimum condition in terms of temperature and precipita-
tion during the growth period of the species. These three equations
fitted to the data for the three species are:
SO TECHNICAL BULLETIN 12
A. Pale Western cutworm....Log Y = 9.48837 — 10 + .01158 X
B., Amy wore ec. 1c eer Log Y == 9.85188 — 10 + .00999 X
Cr aVariepated citwornt = a Log Y = 0.03695 + 00845 X
jx
These soil moisture curves may be used to indicate the distri-
bution of each species by plotting the mean data for any station on
the same graph and comparing their location with the curve.
3. In addition to these general moisture requirements, there are
certain sequences of climatic conditions necessary for the production
of the species in large numbers, which must be fulfilled in any season
before an outbreak can occur. The temperature relations of C. unt-
puncta during the fall and winter months are an example of such a
condition.
4. Of these conditions, those surrounding hibernation seem to he
of the greatest importance, and an outbreak seems to be directly related
to the percentage of the larvae that survive the winter successfully.
METEOR@EOGICAL] RELATIONS OH Eb eA 1D UTe Devi iis
As was already stated, the data relating to the effects of weather
conditions on moth flight were secured at St. Paul, Minn., in 1920,
and at Havre, Mont., in 1921. The Minnesota data were published in
a former paper (Cook ’21) together with a part of the present statist-
cal treatment, and these basic data will not be repeated here.
Bait traps were run at Havre between August 1 and September 5,
when a cold wave and considerable snowfall practically put an end to
moth flight. The traps used were large glazed earthenware receptacles
holding about five gallons each. Eleven of these were used during the
height of the flight season on two fields, being placed about three
hundred feet apart and about three feet above the ground. The bait
used was a 10 per cent solution (by volume) of crude beet molasses,
obtained from the Great Western Sugar Co., at Billings, Mont.
Because of the high evaporation it was found necessary to renew the
solution about twice a week.
A record was kept of the numbers caught of each of the more
abundant species per night, and a comparative count of the males and
females of Porosagrotis orthogonia, which was the species on which
the most accurate data were desired. As the catches for a few nights
at the height of the flight period were too large to be counted by one
individual, the entire catch was preserved for each night by drying,
and later counted by the following method of sampling. The entire
night’s catch was placed in a conical pile on a flat surface, and
separated by planes through the apex into a series of radiating piles,
each of which represented a definite fraction of the catch (one-fourth
or one-eighth, depending on the size of the total catch). One of these
piles was then carefully examined and sorted, and the rest of the catch
Hares
Ly
PHYSICAL ECOLOGY OF THE NOCTUIDAE 31
inerely counted, the total for each species being assigned pro rata from
the proportion found in the examination of the fraction. This method
was found to give results of relatively high accuracy.
Table XII gives the total figures for the more abundant Noctuids,
obtained as described above.
TABLE XII
Motu FLIGHT AT HAVRE, MONT.
AUGUST 1 TO SEPTEMBER 8, 1921
No. of Per cent of
Species specimens total catch
Porosagrotis orthogonia......... Males 6,450 10.8
Females 14,614 24.5
FULOG PAA Pennisi . 5. ace bh chs oo 28,309 47.2
EuUNoG -CuUadridentald Fan . oc 4 chiseled 2,826 4.7
DEDCMIAGEVASEALON On 6 euev ea re we DISYGW 4.3
CarGdrinag Cxlima ca 6 oo ok ek Poe 681 14
Other speciedie cat, oti eee ote te te 4,640 7.4
Total 60,057 100.0
*Included in this record are E. quadridentata, E. dargo, E. ridingsiana, and several other
closely related species.
Included among the “other species” were Chorizagrotis auxiliarts,
Feltia ducens, Porosagrotis catenula, and about twenty-five other
species, mostly of the genus Euxoa, as well as considerable unidenti-
fiable material. None of these species was present in more than one
per cent of the total.
The noteworthy feature of the catch was the great and increasing
abundance of Euroa pallipennis, a species formerly very rare, but at
present the most common single species. So far as is known, the
species is not injurious to crops, but the larva has not been positively
identified.
Records of temperature and humidity were available at the
experiment station from instruments exposed to field conditions within
half a mile of the traps. Pressure observations taken at 6:00 p. m.
were obtained from Mr. C. M. Ling, United States Meteorologist at
Havre, about seven and one-half miles distant. As pressure varies
rather slowly, these readings gave a good index to conditions at the
station. The data for catches, temperature, humidity, pressure, and
precipitation, together with the five-day sliding average for each, com-
puted as in the former page, are given in Table XIII. The normals,
which were not computed for the weather factors in the Minnesota
data as published, were also computed for these factors, but the
figures are not included. Plate V is a graphical representation of
Table XIII. For each factor are shown a straight line representing
the seasonal mean, an angular graph showing the daily variations in
the factor, and a smoother curve closely approximating the five-day
normals.
» ~ me:
v v ¥ re »:
dOPIL ,
eee ere er ee ee ee SE SS ee ee
98°0 TO rar ETELZ rors SOE O01 Sac pearean ze Taakane ages 00 0 Il 6
$0°0 5 AOR ar Ke OSZ'LZ FRC sayy FL eishere Stee St 00 0 II g
$80°— S8C° LC OOC LT co— cs ee et SS 89 Poot 6°C6 C LST PEL IT L
FIO OLE LT £67 LC eS tara £V ce c 09 c9 VcS¢ 6°£6 8°9ET 909° (Y): 9
810° C8C LT O9E°LC Sse ce Ce \! co £9 6OVL o'r6 LOL SLL Tl ¢
670° POT LT £60 LC 9 ce 54 tlicg £9 09 LEG Tae SP €S Il v
$00 810° LVC LT S97 LC ¢ ce c¢ er, F9 8S (GN! SLE CC 6 v £
VSO COT LC 601 LT v LC ihe S 89 €L TL0d T1697 O'LSS 9ET'9 IT c
F60° CIV LE 90T LT ie tC £C SoS €L 89 16S O'LCV VcSc SLL Z TI T “3dag
UL Gees OTT Le Ch69C Lh. = £C oT S OL 18 V16 6°6LS 8°6CS O£8'sS ia Te
DOTas OFT LC OFO'LT Vis O07 oT 5 SL £8 O'vET O'FOS 6 VOL 60S'8 IT oe
belts SOT LC 960° LC L £C Oe ‘ene 08 HE GOT £889 0991 8616 cl 6C
000° BPC LE BPC LT ib SC tl C 6L 18 6°66 0'Sc9 £Vc9 96F'L cl 8C
Ome CIE LE 667 LT 6 8C |S I OL LL SOTT 8°06F byes $838'9 cl LC
090° 867 LC BSE°LC £ LC 10} 3 Be LL OL 8° TOT OVSE COE Ore 'F cl 9C
PAP L8C LC O9E"LT Cea: Oe LC doe OL CL OCS SOC 8°6cl BSs'T ct Sc
LU 667 LT OCC LE (is 87C 9T S SL O08 S525) Tort £8 06S L VC
OL0ig TLE LC COV LE v LC ize c We LL 9°00T 918 C8 6ce v £G
660° 6S7LC 8SE°LT oa 6C 8C Sa GL OL 6 OFT £°09 S88 LEY Cc (a6
(OO OTE LC OIC LC Oe ote £¢ it el VL 8°9P c OP OSC 69 £ TG
tt0 — fVe Le 667 LT Shee bY 6£ 9 69 Se ¢°69 OE se 4 TZ ts. 0c
LEC 860 LC SCS LC ORS Os UY Gros OL 89 COST Vst £°8C $8 £ ol
£0°0 £00° CTE LC OTE LC LC Lhe t8 Ol— 69 6s 0'0F Sele O'L IC ba 8T
80°0 Cri POT LT CEV LE i 09 19 I 89 el 199 Oct 9°8 9¢ S LI
£80° 607° LC COC LT Cay 6S BS vas WWE OL V SEC s°8 0'0¢ 08 v OT
aml) FOC LST LE £SO'LC 4 Os vs oe Zs We CaSil OL ctl 5 4 cl
660 — OSELT TSC LE i oF Le 8 ch 18 C8 69 PS £C 14 a!
SLU C8E°LT LSS LC irs oF OF c TL OL £99 £9 CV LI v eT
sel SSP LC 96S°LC OT eV 6S Saar UL 99 VCC SOE Hike: Si! 4 cl
Og COV LC TSF LC Vs te ev o£ Cc SL sid Pes v'0C OLT 89 4 IT
cs0° T8e°L7 CLV LC eee OF 6£ ioe SL We V'SEC Tce O'cS 80C 4 Or
Src LIE LC PLO LC 9 ce Be 0 SL 8L Tae dee 9°CC GSC TOT v 6
Oo) ane OTe Lc cSh LC LL os’— 90° = rero+ qee+ ett NE Tf Ae eek Fee Det Jey A}Iprun yy -yoye_ jess 10°— (1c LO°= tI— we
Ih 70+ | o¢°+ £0 91. Oc + Heese gangeied ute T -Yo3eD Or= lk Bo 90° = O£°+ at Ais
jenzeg | ]e1OL jenieg [e190 L povee1109 jenieg [e10L jenieg [ROL
rd $10}De me
PUR UO; PJOSOUUTY eueUOofy PIOSOUULY
(IIIX ATAVL ‘FT ‘TT “8 ‘¢ suumnjoD) (IIIX ATAVL ‘ST ‘ZT ‘6 “9 suunjo))
S10}DE} MVEUII]D [PULION sjeuliou wo1j soinziedegd
YA Yo ved [RULION—D dnoiy YWWIA yo eo xopuy—g dnoisy
l= of°+ ‘dy OY 80° Lb + dy} oy UOHLe1I09 Vd [NW ZV 97+ dy} ‘Oy LO'* St°+
£0'+ OR ee al a oinsse1q-A}Ipruin Lor
Co OF el os ee dInssoig-9in}e1odula LT 0Fi—
St Lb “os AqprunFy-91n}e19dw9 TL cr
OFL = 70 = £0°+ TO’ 60°+ BF Lg en sINSsetq-YI}e-) Oka ie he Be CO S00 ILO =
VEL FPG LG O80 Se lee ame 0 Pa ce ee Nae A}Iprun FY -Yo3e +) Of FO 07+ 180° T€°+-
OFL'= O1'+ L Ver Z7OU = CO + GF ea Gale oinjzerodutea J -Yoye +) Oe ZOn |i Ee 680° 87° +
jenieg [e10.L [enieg [eI peve[e1109 jenieg [R10 L [eaeg
$10}0eY =
(%0¢) Puvwoy (%0¢) Byosouuryy (%Or) euequoy (%PFS) Bposouuryy
wuinujdo sAoqe AyIpruny, wnuiydo Mojeq AyIprunyy
(IIIX ATAVL ‘ET ‘OT *£ ‘9 SNWNTOD)
SHNIVA GHAXASAO GNV HOLVD XAGNI—y dnousy
SUYOLOVY TVOIDOIONOALAJY HLIM LHDITY HLOJY AO SNOILVIANNOD
AIXPA TS VL
36 TECHNICAL BULLCETING?
Considering the coefficients of Group B, we have a much different
condition. In this set of correlations, the effects of variations in the
factors were studied, and variations in humidity have the smallest
effect of any factor studied. Temperature and pressure both have
significant positive correlations, which may be interpreted as follows:
When the temperature and pressure are higher, and the humidity
lower, on any particular night than the averages of these factors for
the five nights.of which this one is the center, then the catch is also
higher than the average for these five nights. That is, moths fly more
freely on warm, dry nights, following cooler, damper nights than when
the reverse is true.
It is in group C that the largest values are found for the correla-
tion coefficients. As the figures correlated are averages for five-day
periods, the relations must be considered as being relations of the
weather factors to emergence. Thus, under Minnesota conditions,
more moths emerge in a time of higher temperature and lower pres-
sure and higher humidity than the season average, the humidity being
the most important factor, followed by temperature and pressure. In
the Montana data temperature was of practically no significance, but
there was a very high relationship between emergence and the other
two factors, with humidity slightly more important. Evidently, more
moths emerge in times of high humidity in humid regions, and more
moths emerge in times of low humidity in arid regions. The size of
the coefficient of multiple correlation in the latter case, “R’==+ .92,
indicates that the emergence of moths in the arid regions is almost
entirely a function of these climatic conditions.
To summarize these relations; the observed values of humidity
have an important bearing on the flight of moths, the largest numbers
flying when the humidity is near the seasonal mean. Humidity also
affects emergence, more emerging under high humidity conditions in
Minnesota and under low humidity conditions in Montana. Varia-
tions in temperature and pressure from night to night are of more
importance than variations in humidity. Further studies, and the
accumulation of more data may affect these relationships, but probably
will only intensify them.
CDN C EGS LONG
A general consideration of the studies presented in this paper leads
to the following conclusions:
1. Each of the species included in this study has a very definite
optimum soil moisture requirement, which, broadly speaking, limits
the distribution of the species.
¢)
\
PHYSICAL ECOLOGY OF THE NOCTUIDAE 37
2. This requirement may be determined experimentally under
controlled conditions, and also indirectly, by a statistical analysis of
the weather conditions surrounding outbreaks of that species.
3. In each case, the optimum moisture requirement of the species
which occur in any given region is a close approach to the normal
climatic condition in that region, so that outbreaks would occur every
season were it not that there is also a necessary seasonal sequence of
conditions which must be fulfilled in order to enable the insect to
reach destructive abundance.
4. This sequence, which may operate either by favoring the
destructive insect, by limiting the activities of its enemies, or both, 1s
the controlling factor in the production of outbreaks, and a careful
study of such a sequence in the life history of any insect should enable
us to predict the possibility of an outbreak of that insect in any given
region.
In conclusion, the writer wishes to emphasize the importance of
the use of mathematical methods in the study of insect outbreaks, as
well as to show its practical application in the examples cited. As the
literature of statistics is rather foreign to entomological workers, a
few selected titles of especially valuable works, which are of great
service in such a study, are listed in the bibliography.
BIBLIOGRAPHY
REFERENCES ON STATISTICAL METHODS
Ball, John. Climatological diagrams. Cairo Scientific Journal, Vol. iv, No. 50.
(First use of the Climograph.) 1910.
landers, V. B. The Use of Charts and Graphs in the study of climate. Mo.
Weather Rev. 50:481-484. Sept., 1922.
Leland, Ora Miner. Practical least squares. McGraw-Hill Book Co., N. Y.
1921.
Lipka, Joseph. Graphical and Mechanical Computation. Part I. Alignment
charts, Part IJ. Experimental Data. John Wiley and Sons, N. Y. 1921.
Smith, J. Warren. Agricultural Meteorology. Macmillan, N. Y. Rural Text-
book Series. 1920.
Varney, B. M. Some further uses of the climograph. U. S. monthly weather
review, Vol. xlviii, No. 9, pp. 495-497. 1920.
Yule, G. Udny. An introduction to the theory of statistics. Fifth Edition.
London, Charles Griffin and Co., Ltd. 1919.
LITERATURE CITED OTHER THAN STATISTICAL
Barrett, Charles G. The Influence of Meteorological Conditions on Insect Life.
Ent. Mo. Mag., Vol. xix, pp. 1-8. 1882.
Cook, William C. Studies on the Flight of Nocturnal Lepidoptera. 18th Rept
State. Ent. Minn. for 1920, pp. 43-56. St. Paul. 1921.
Cooley, Robert A. Observations on the Life History of the Army Cutworm
Chorizagrotis auxiliaris. Jour. Agr. Res., Vol. vi, No. 23, p. 871-881. 1916
Criddle, Norman. Precipitation in Relation to Insect Distribution. (Popula:
and Practical Entomology) Can, Ent., Vol. xlix, No. 3, p. 77-80. 1917.
38 TRG NICAL SGA T shims
Fitch, Asa. Sixth Report. on the Insects of New York, p. 121. (Weather and
the Army Worm.) 1860.
Folsom, Justus Watson. Entomology with Special Reference to its Biological
and Economic Aspects, 466 p. Philadelphia, P. Blakiston’s Son and Co.
1906.
Hampson, George F. Catalog of the Lepidoptera Phalaenae in the British
Museum. iv. Noctuidae, Agrotinae, 1903, v., Noctuidae, Hadeninae, 1905, vii,
1908, and 8, 1909, Noctuidae, Acronyctinae. London, printed by order of
the trustees. _
Henry, Alfred J. Climatology of the United States. U.S. Dept. Agr., Weather
Bureau, Bulletin Q. 1906.
Hopkins, Andrew D. Periodical Events and Natural Law as guides to Agri-
cultural Research and Practice. Mo. Weather Rev., Supp. 9. 1918.
Jones, Thomas H. Miscellaneous Truck-Crop Insects in Louisiana. II. The
Granulated Cutworm, an Important Enemy of Vegetable Crops in Louisiana.
U. S. Dept. of Agr. Bul. 703, pp. 7-14. 1918.
Knight, Harry H. The Army Worm in New York. N. Y. (Cornell) Agr. Exp.
St. bul23/6, 4 1916.
Merriam, C. Hart. Life Zones and Crop Zones of the United States. -U. S.
Dept. of Agr., Biol. Surv., Bul. 10. 79 p. 1898.
Parker, J..R., Strand, A: Li, and Seamans, H. L. Pale Western Cutworm
(Porosagrotis orthogonia Morr.) Jour. Agr. Res., Vol. xxii, No. 6, pp.
289-321. 1921.
Pierce, W. Dwight. A New Interpretation of the Relationships of Temperature
and Humidity to Insect Development. Jour. Agr. Res., Vol. v, No. 25, pp.
1183-1191. 1916.
Riley, Charles V. Second Report on the Insects of Missouri, p. 45. (Confirma-
tion of Fitch’s theory.) 1870.
Eighth Report on the Insects of Missouri, p. 50. (Same.) 1876.
Sanderson, FE, Dwight. The Influence of Minimum Temperatrue in Limiting
the Northern Distribution of Insects. Jour. Econ. Ent., Vol. i, No. 4, pp.
245-262. 1908.
and Pearis, L. M. The Relation of Temperature to Insect Life. New
Hampshire Agr. Exp. Sta., Tech. Bul. 7. 1913.
Slingerland, Mark V. Climbing Cutworms in Western New York. N. Y.
(Cornell) Exp. Sta. Bul. 104, Nov., 1895.
Smith, John B. Contribution Toward a Monograph of the Lepidopterous
Family Noctuidae of Temperate North America.—Revision of the Species
of the Genus Agrotis. Bul. 38, U.S. N. M. 1890.
Strickland, E. H. The Army Cutworm, Euroa (Chorizagrotis) auxiliaris Grote.
Canada Dept. Agr., Ent. Branch. Bul. 13. 1916.
Thompson-Seton, Ernest. Life Histories of Northern Animals. 2 vol. Charles
Scribner’s Sons, N. Y. 1909. (Map of faunal regions of North America,
VOLViAD. 155 .
Turner, W. B. Female Lepidoptera at Light Traps. Jour. Agr. Rs., vo. xiv,
No. 3, pp. 135-149. 1918.
BIOGRAPHY
William Carmichael Cook, son of Guy Reuben Cook and Ellen
Ilizabeth Cook, was born at Syracuse, New York, October 2, 1895.
lle attended the public schools of Syracuse, graduating from Central
High School in 1913. He attended the Agriculture College at Syracuse
University from 1913 to 1916, and the same at Cornell University
during 1916 and 1917, receiving the B.S. degree at Cornell in 1917.
During the summer of 1917 he did field work for the Entomology
Department of Pennsylvania State College. From 1919 to 1922 he did
graduate work in entomology and insecticide chemistry at the Unt-
versity of Minnesota, doing field work with the State Entomologist
during the summer seasons. He received his M.S. in 1920. Since
May 1, 1921, he has been in the employ of the Montana Experiment
Station, completing his graduate work on leave of absence in 1922.
He was married to Muriel M. Amidon, of St. Paul, Minnesota, on
July 22, 1920.
Previous publications:
1920. Cut worms and army worms. Cir. 52, State Ent. Minn.
1921. Studies on the flight of noctiirnal lepidoptera. 18th
Rept. St. Ent. Minn. pp. 43-506.
FINO
3 0112 072856195