6 



abundance of natural enemies which miglit prove disastrous to the spe- 

 cies sliould all appear at once. 



In the latitude of Washington, D. C, the first brood of larvae practi- 

 cally all disappear from the trees by the end of June, and the first flies 

 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 this 

 second brood of flies that is particularly disastrous to the trees, 

 although the spring brood of larva^ is often sufficiently abundant to do 

 verj' 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 i\y, determined by Westwood as a species of 

 Encyrtus, wliich stings 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. Tlie 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 clirysalis therein, and ultimatel}' 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, 

 D. C, of this or some related parasite, but failed to secure the adult 

 insect. 



REMEDIES AND PREVENTIVES. 



In the effort to exterminate this insect the slimy covering exuded by 

 the larvffi in such copiousness was formerly 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 spraj' the plants 

 with an arsenical wash or with a simple soap solution. Tlie larvae are 

 delicate and easily killed, and as they eat almost exclusively on the 

 upper surface of the leaf where the poison can be most easily placed, 

 thej^ get the greatest amount of it and are the easiest of all larvffi to be 

 thus exterminated. The plants may be sprayed with Paris 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 be effective must be applied at a strength of one- 

 half pound of soap to a gallon of water, first dissolving the soap, prefer- 

 ably whale oil, l)y boiling in a small quantity of water. 



