LIBRARY STATE PLANT BOARD " liarch 1943 E-588 United States Department of Agriculture Agricultural Research Administration Surea.uof Entomology and Plant Quarantine THE FIELD STATUS OF PARASITES OF THE EUROPEAN COM BORER AT THE CLOSE OF 1941 By Charles A. Clark, Division of Ceveal and Forage Insect Investigations The introduction and establishment of foreign parasites and the increas- ing importance of this biologic factor in the natural control of the European corn borer (Pyrausta rubilalis (Kbn. )) in various localities in the United States have led to a development in the parasite situation which ay be follow- ed in this report in conjunction with similar reports listed in various supple- ments of the Insect Pest Survey Bulletin^.' of the United States Department of Agriculture. The status of the corn borer parasites in the field has not been and is not now in a static condition. There h*s been a considerable 'enlargement in the size of the territory in which the exotic parasites are attacking the borer, a.nd this improving condition can be expected to continue as the parasites dis- perse into previous] y unoccupied territory and as additional releases are made in new and widely separated localities. In several localities the parasites have become abundant enough to cause appreciable mortality in the. borer popula- tion. At the close of 1941, parasite surveys were conducted at 12 localities located in or including parts of nine States. The size of these areas ranged from 7 square miles °t a locality in Michigan to 2,375 square miles in south- eastern New England. A total of 19,273 host larvae were collected, isolated in individual containers, and observed for parasitization. Of the 17 species of larval parasites of the corn borer imported from Europe and the Orient and re- leased in thp United States, only the 5 species discussed in this report were recovered from the collections made at the close of 1941. A summary showing the status of these five — Chelonus annul ipes Wesm. , Eulophus viridulus Thorns. , Inareolata pur.ctoria (Roman) , Lydella grisescens R. D. , and Macrocentrus gifu- ensis Ashm. — is given in table 1. The figures on borer para.sitization in table 1 tend to be low since the territory covered by most of the survey localities included locations at the perimeters of parasite dispersion. Parasitization near the center of release points where the pairasites have been established for some time are in most cases somewhat higher, and in some localities much higher than the table figures. 1/ The supplements referred to are found in the following issues: Vol. 18, No. 9, Dec. 2°, 1933; Vol. 1°, No. 3, Oct. 15, 1939; Vol. 20, No. Dec. 1, 1940; Vol* 21, No* 9, Dec. 15, IQ41. 2 - O CQ o 0 P -P cd CQ 0) ■H P ■H rH a o o rH CO P o •H a CD rH cd Eh !« ' CQ , § I , O !>>H s!o Ol •H CQ •P P CO P N P •H £ P CD •H O CQ O CO rH Ph O co co pm S 0 CD i Ph! 03 CO, o rH, cd; Ph. m 1 • 03 -P P P CD. CD > 0 > rH CQ a1! 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CD CQ 3 Ph tiD rs ft P M o P rH rH rP ■H Fh ,y o CQ ^ W P: fl M p< CO P M CQ p CO .P T3 M P ■P p Fh CQ rH P CD, p •H CD p •H 0 >5 U • p (0 p O ^ PI 3 o Pi O T3 CD rH Ph CO rH Ph" CO P P 0 o P rp o eu) 0 E^ CO -H W O CD CD >H ■3 r-J o rH •H CQ rH r^ P g c ■H •H CQ g co O W o 3 W3 CO P CO o CO o ,p p CQ L3 3 3 r- pq (H W o ^ o •H CO pq o M Eh" CO CD o CD (D •H 0 rCJ •H S a o S £ i> & o s * -3- Lydella grisescens R. D. Tne introduced tachinid Lydelia grisescens is present east of Worcester and Fitchburg, Mass. , but borer parasitization by it is low throughout most of this territory except near the shore around Buzzards Say, where parasitization by the tachinid in several collections vas over 25 percent in 1941. In control Connecticut. Lyd-: 11? ;risescens has spread rapidly end is now present over approximately 1,400 square miles. It is nore abundant -est of the Connecticut River than east of it. Parasitization is rather low, but in indi- vidual fields it often exceeds. 10 percent. In New Jersey Lydelia grisescens is present in an area of over 227 square miles around the town of Colt's Neck in Monmouth County. Individual collections were often 20 percent parasitized, and the average was from 3.5 percent at the close of 1940 up to £ .1 percent at the close cf 1941 in the central portion of the surveyed locality. This parasite had attacked 20.7 percent of the 3,177 hosts collected in Burlington County. iviany collections showed over 25 percent parasitization by this species, several 50 percent, and one over 85 percent. It has crossed the Delaware River from Burlington and is present in Bucks County, Pa. Lydelia grisescens was the only parasite recovered in Virginia at the close :>f 1941. It had parasitized over 10 percent of the hosts in two collec** tions obtained near the laryland State line in northern Accomac County on the Eastern Shore of Virginia. It was present, but scarce, in the central part of the Eastern Shore around the town of Onley. An informal survey showed that it *as abundant in a limited locality around a recent release point on the main- land near Back Bay in Princess Anne County, Va. This parasite was also present and abundant along the shore of Lake Erie. The average borer parasitization »as 32 percent at Sandusky, Erie County, Ohio; 23 percent near Toledo, Lucas County, Ohio; and 24 percent in Monroe County, Mich. In one collection in the last locality 75 percent of the hosts collected were parasitized by this tachinid. Inareolata punctoria. ( Roma.n) Another parasite, Ina.reola.ta. punctoria, is present over an area of approxi- mately 600 square miles in eastern ifessachusetts. At the close of 1941 it 'as only about half as abundant as usual in this Sta.te, probably because -of the very lo^ status of the corn borer population. The parasite was recorded in Rockingham County, H. H. , '"here it ha.d parasitized 13 percent of the borers observed. I. punctoria is present over a territory of approximately 800 square miles in central Connecticut, where it is the most important parasite present. It is continuing to spread and increase in this State. This ichneumonid is firmly established at the more recently established parasite release point in Monmouth County, N. J., where it is present over an area of 30 square miles. It is also present in a locality of approximately 50 square miles in western Ne™ York State around the •Cattaraugus Indian Reservation, but borer parasitization 'oy it was low here at the close of 1941, being only 2.7 percent of the nosts observed. UNIVERSITY OF FLORIDA - 4 - Macrocentrus gifuensis Ashm. 3 1262 09224 7203 The polyembryonic braconid Macrocentrus gifuensis is well established in southeastern Massachusetts, central Connect i^tTT and Monmouth County, K". J. It was most important in Massachusetts, where borer parasitization was lower in 1941 than for several years previous, but nevertheless in several collections over 25 percent of the hosts observed had been killed by this parasite. At the newer points of establishment in Connecticut and New Jersey the species 'is neither widely distributed nor abundant as yet, but it seems to be paralleling in proper sequence the history of its rise in southeastern Massachusetts. Chelonus annul i pes lesm. An imported parasite recovered in southeastern Massachusetts, central Connecticut, and the Hudson Biver Valley of Kew York is Chelonus annul ipes. It is of little importance in any of these localities and may not survive in the last t^o, since the specimens recorded were few in number and represent recoveries from relatively recent releases. Eulophus viridulus Thomson An introduced parasite that was unreported for a number of years has ^ in- creased steadily in the last few seasons in Lucas County, Ohio, and was again recovered in Monroe County, Mich. This is Eolophus viridulus. It was much more numerous at the close of 1941 than in 1940, but borer parasitization is still low (3.1 percent in Ohio).