Circular no. 26. Second Seri(S. I iiiicil States DiMuiiiiitMn DIVISION OF KN IOMOI.OGY. I'll i: PEAH SL1 ».. / rnul, s It 11,11, i mi |;> i M \i; \i ii BIS in - \\i> in- ["ORY The damage to the foliage i>f the pear, cherry, plum, an from the slimy slug-worm is familiar t<> every fruit grower. Tun or three generations of these Blug-worms, or ' ' -In ■ also termed, appear during the Bummer and frequently in Buch extraordi- nary numbers, with the later broods, thai the leaves "i the attacked plants turn brown, die, and tall to the ground in midsummer, and tin- new growth "I foliage which ifterward thrown out is o ft e n similarly destroyed. Trees thus denuded air much checked in growth <>r greatly injured, if not killed. When the -lu'js are very abundant, as they frequently are in July during the second brood, the Bound of the eating of myri- ads of mouths resembles somewhat the falling of line misl <>r rain on the leave-, and instead of one or two larva at work on a leaf there may he upward of thirty. Under such circumstam very distincl and disagi able odor is disseminated by the multitudes of slimy slug-like creatures. The slug-fly is a -mall, glossy black insect, considerably less in than the house fly, measuring only aboul one-fifth of an inch in length. The win:;-, which are four in number, are transparent, iridescent, and have a -moky Kin. I across the middle, which varies in intensity in dif- ferent specimens. It belongs to the family commonly termed " saw- flies," (Tenthredinida ) on account of the Baw-like instrument or ovipositor with which the female insect places it- eu'i:- in the leavi other -oft parts of the plant. > adult -;r.v » iih sltmi In norma 1 2 The pear blag is an old enemy of fruit trees, and while it has been known in this country for over a hundred years as an American species, the interesting fact that it is the familiar slug-worm pest of the pear and plum trees of Europe has not hitherto been definitely ascertained. In Massachusetts, toward the latter pari of the last century, this insect became very destructive, and Prof. Win. I). Peck prepared an admira- ble, illustrated account of it under the title of " Natural History of the Slug Worm," which was printed in Boston in 17!'!) by the Massachu- setts Society for the Promotion of Agriculture. The author obtained for the production the society's premium of $50 and a gold medal. The account of this insect given by Professor Peck is fairly complete and accurate, hut for fifty years it has been out of print and inaccessible, and I have not been able to consult it. Harris abridged and condensed it for his account of the slug-worm in his "Insects Injurious to Vegeta- tion." published in 1841, and later writers have generally followed Harris. In Europe this insect was one of the first of the injurious species that attracted attention, and one of the earliest of the economic writers on insects, Reaumur, in the fifth volume of his bulky work published in ITllt, gives a short account of it, together with recognizable figures of the insect in different stages, illustrating also the effect of its work on leaves. The first description and name which stands out unquestioned is by Retzius (1783), who describes the species as Tenthredo limacina. Linn'e, in descrihing what seems to have been an entirely distinct in- sect, which he called Tenthredo cerasi, quotes Reaumur's account of the slug-worm, which he erroneously took as belonging to his species, and very generally since, therefore, the former has been called cerasi Linn. (Cameron.) Professor Peck in descrihing the insect gave it the name suggested by Linne, and was of the belief that the species occurring about Boston was at most a mere variety of Linne's species, meaning, however, the common pear-slug fly of Europe. Later American writers have treated it as a native species, and under the generic name of Selandria or Erio- campa, Peck has had the credit lor it in this country, and the fact that Peck himself associated it with Linne's species has been generally overlooked. That the species so common in this country is identical with the slug- fly of Europe has been fully established by a comparison of specimens from Europe with abundant American material. In Europe this insect has heen the suhject of description by innu- merable authors, having received at least nine different specific names and having heen referred to some eight genera. In this country it has also heen the suhject of many short notices, hut of very few full accounts other than the one published by Peck. The i" ii ! ! " pel which i en ilj di tributed \\ itli the Boil about the pi ante which il infests, and it hue I ried about the, world until it has made its waj into practii allj everj civilized country. Ii is known at least td occur throughout Europe and America and in many of the British colonies. The Blugfi have been round on 11 many different plants, Reaumur recording them on the plum and cherry, and especially pear, bul also on the oak. and a recent catalogue by Dal la Torre indicates their occurrence "n over thirtj different plants in Europe Certain Btone Fruits and the pear, particularly the lattei their especial fa> nril i I I - -:""~--'- I I. II I. HISTORY Wl> II M:i i 8. TIic parent il\ may !"• seen on the pear or othei trees which Berve .1- food for the larva' very early in the sprin . In Washington, D. C, the present Beason thej were observed on the new \\ ex flHPH panded leaves by the middle i>f April actively engaged in / laj ing their eggs. In the lat- /• itude nt Boston and northward the flies do not appear much before the middle of May. and the egg-laying is chiefly during the lattei pari of May and first nt' June. Judging from our experience here many of the laid by the flies which appear in April perish during the cold wet weather which often characterizes this month. This wa> notably the case the present Beason, few, if any, of the eggs first deposited producing larva . But one egg is deposited in a place, and it i- always inserted From the nniler Bide of the leaf. The ovipositor is thrust obliquely through the leaf to the upper epidermis, bul not piercing the latter, and Bhows there distinctly through the transparent upper skin of the leaf, as rep- resented in the accompanying illustration (fig. 2), while the insect titherw ise is completely hidden. The saw -like instrument, when brought into the position noted, is moved rapidly with a swinging lateral motion from siile tn Bide, cutting the upper epidermis free bo a- to form an irregular cell or pockel of peculiar flattened ovoid outline. The egg is quickly passed down between the plates of the ovipositor and dropped into the pockel thus made, the time occupied being a little ovei one minute for the entire operation. I lllustrattm and emergence ol larva a, cutting ol cell i epidermis, w Ith ovipos u im- larged (original). Usually before placing the egg the fly runs about rapidly over the upper surface of the leaf, examining it carefully, and then goes over to the under side to insert an egg, after which she reappears on the upper surface of the leaf and rests for a minute or so before flying to another leaf. it often happens that a good many eggs are deposited in a single leaf, hut I am convinced that this is usually by different flies or at different visits by the same individual. The loosened epidermis about the egg dries somewhat, and the egg-cell soon appears as a minute brownish spot with the almost colorless egg showing at the center. '1'hc egg is oval, slightly flattened on one side, and remains in its peculiar cell (see fig, 2. I>) for a period of about two weeks before the larva escapes. It is so placed in the leaf that it can be readily watched and its gradual increase in size by absorption from the leaf and the development of the young larva can he easily studied with a hand lens. The larva emerges on the upper surface of the ^|# leaf through a very regular semicircular cut y which it makes near the center of the cell. At first it is (dear or free from slime and in color nearly white, except the yellowish-brown head; hut almost immediately the slimy or gluey olive- colored liquid begins to exude over its entire body, giving it the appearance of a minute slug, Pro. 3.— Pear slug: «. last ... -i .• , • , • ,, •. i. moulted larval skin: 6. larva '"' Sof1 snal1 ' from wmch ]t g ets lts name - Its after easting last skin- head is dark brown, appealing black under the somewhat enlarged (orig- ,. , ., , -. , , , ,, taal) slime, and the body also becomes almost equally dark. The anterior segments are much swollen. covering up and concealing the head and thoracic legs. In common with other saw-fly larv;e it has a great number of false legs or prolegS on the abdominal segments; in this species there are fourteen such prolegs, the terminal pair being wanting, and the tapering tip of the body is usually slightly elevated. As soon as the larva emerges from the egg it begins feeding on the upper surface of the leaf, eating out small holes or patches about the size of a pin head or smaller, hut never eating entirely through the leaf. The larva' feed almost invariahly on the upper side of the leaves and the minute eaten spots which they make at the start rapidly increase in si/.e until much of it. hut not the entire surface of the leaf, is denuded, leaving merely a network of veins, or a leaf skeleton, held together by a nearly intact lower epidermis. Leaves thus eaten turn brown, die. and fall to the ground, the tree being frequently defoliated, except for the effort it usually makes to put out a new growth. The characteristic features of the larva are its swollen anterior imiit- and its olive-colored slimj covering, which last i probablj a pro ti. thui furnished \>\ nature against the attacke ol parasiti< insects. It is \kin. The larva due- nol feed after this moult, hut crawls down the plant to the ground, which it burrows into actively, dis- appearing beneath the Burface in a very short time, it penetrates to a depth of from half an inch to two or three inches, usually the lesser distance, and at the extremity of the 1 oon: b, burrow presses the soil away from itself so 11 11 -i enlarged (oriirii as to form a little cell or chamber, the Bidi - of which it moisten- with saliva. The drying and hardening ol the walls of the chamber form a sort of f turn texture and more ,,i less impervious to water (see fig. I. a). During the heated season of July and August the transformation from the larval to the pupal Btage and from the latter to the adult insect is quite rapid, the pupal Btage being assumed in from -ix to eighl days, and the adult flies transforming and digging out through the soil some twelve Or fifteen day- alter the larva entered it. It ,-eem- Iroin the studies by Peck, and in part confirmed by my own observations, thai all of the larva of the spring brood do not transform at once, but some few of them remain unchanged as contracted dormant larva' over w inter to transform the next spring. It is true also of the Becond broods of larva' thai some of them come oul the same season, while others remain over winter and do nol pupate until Bhoitly 1 the appearance of the adults in April and May. The holding over to the next year of certain larva of each brood is doubtless a provision ol nature to prevent the extermination of the species by any untoward ai 1 i- dent, such a- the absence ol food, unfavorable climatic condition 6 abundance of natural enemies which might prove disastrous to the spe- cies should all appear at once. In the latitude of Washington, Q. ('.. the first brood of larva' practi- cally all disappear from the trees by the end of June, and the first Hies of the second brood begin to appear about June 20 and are out in greatest number about the first of July. It is the progeny of tins second hrood of flies that is particularly disastrous to the trees. although the spring brood of larvae is often sufficiently abundant to do very serious injury. NATURAL ENEMIES. The slimy repellent covering of the larva does not altogether prevent its being preyed upon by parasitic insects, and in Europe some half dozen parasites have been reared from it. In this country Peck men- tions a minute parasitic fly, determined by Westwood as a species of Encyrtus, which stints the egg of the slug-fly through the upper epi- dermis of the leaf, placing in each egg of its host a single one of its own — much more minute. The little parasitic maggot when it hatches finds food enough within the egg of the slug-fly for the needs of its full development, changes to the chrysalis therein, and ultimately emerges a perfect fly like its parent. So abundant is this parasite at times, as reported by Peck, that the second litter of eggs is sometimes nearly all destroyed. I have found evidence of the occurrence at Washington. I). C, of this or some related parasite, hut failed to secure the adult insect. REMEDIES AND PREVENTIVES. In the effort to exterminate this insect the slimy covering exuded by the larvae in such copiousness was formerhy taken advantage of and applications of various powders and dusts were made to them, such as ashes, lime, or road dust, with the object of having it adhere to their viscid surface and kill them. Under this treatment, however, the larva usually merely sheds the incumbered skin and starts in life afresh with a new coat. The best means of destroying the slug-worm is to spray the plants with an arsenical wash or with a simple soap solution. The larva' are delicate and easily killed, and as they eat almost exclusively on the upper surface of the leaf where the poison can he most easily placed, they get the greatest amount of it and are the easiest of all larva' to he thus exterminated. The plants may he sprayed with Parks green or other arsenical wash at the rate of 1 pound of the poison, mixed with an equal amount of lime, to 250 gallons of water. The soap wash to he effective must he applied at a strength of one- half pound of soap t<> a gallon of water, first dissolving the soap, prefer- ably whale oil. by boiling in a small quantity of water. Where one has bu( fe* plants to rnraj and do. ,„ arsenical or the soap wash, hellebore maj be used either as a drj powder or wa wel Bpray. The powder maj be applied with a bellows ,„• dusted lightly over the plants from a cloth bag, making the applica- tion preferablj when the plants are wel with dew. So sensitive is tl worm that very 1 nil oftei ,, m ,| „ is much less apl to be injuriou in wel us. Fo. this ,n h maj often be possible 1 1 plants ol il bj subjecting them t,. ;i forcible water Bpray. C. L. M IBLAl I First Assistant Entomoh Approved : .1 \\ii> \\ ILSON, § /■« tary of Agrit ulturi . \\ L8UINOTON, D. C, August :' s - 1897 o UNIVERSITY OF FLORIDA III I M 3 1262 09216 4838