202 EEPORT UPON COTTON INSECTS. 



This concludes our list of hymenopterous parasites of the cotton- 

 worin. The remaining five belong to the order DIPTEEA, or two-winged 

 insects. 



THE TACHINA FLIES (Dipt., family TcwMnidae).Two of these two- 

 winged parasites belong to the family Tachinidae. The members of 

 this family are parasitic upon other insects, the females depositing their 

 eggs upon the bodies of caterpillars, &c., and the young larvae hatch- 

 ing, penetrate into the interior of the body and live upon the fatty por- 

 tions of the victim. The number of eggs laid upon a single caterpillar 

 varies with the size of the caterpillar. Serville is said to have reared 

 as many as 80 specimens from a single larva of Acherontia atropos. I 

 have frequently observed as many as 15 to 20 eggs of Nemoraea leucaniae, 

 Kirkp., upon a full-grown larva of the army-worm of the Xorth (Heli- 

 ophila unipuncta. Haw.). Eight seems to be the largest number which 

 has been found upon the cotton-worm. 



These Tachina flies have much the appearance of the ordinary house- 

 flies, but are usually larger. Their eggs are tough, white, opaque, 

 oval, and somewhat flattened on the side towards the body, to which 

 they are firmly attached by a gum insoluble in water. With the slug- 

 gish caterpillars these flies have little difficulty in depositing their eggs 

 when, how, and where they please. They always place them upon the 

 back of the head, or on the first three or four segments of the body, in 

 such a position, in fact, that the caterpillar can in no way reach them. 

 With flying insects, however, the case is more difficult. We quote from 

 Report of the the Entomological Commission on the Rocky Mountain 

 Locust : 



The slow-flying locusts are attacked while flying, and it is quite amusing to watch 

 the frantic efforts which one of them, haunted by a Tachina fly, will make to avoid 

 its enemy. The fly buzzes around, waitiug her opportunity, and, when the locust 

 jumps or flies, darts at it and attempts to attach her egg under the wing or on the 

 neck. The attempt frequently fails, but she perseveres until she usually accomplishes 

 her object. With those locusts which fly readily she has even greater difficulty; but 

 though the locust suddenly tacks in all directions in its efforts to avoid her, she circles 

 close around it, and generally succeeds in accomplishing her purpose, either while the 

 locust is yet on the wing, or, more often, just as it alights from a flight or hop. 



The parasitic larva, when ready to hatch, eats its way through the 

 egg on the side towards its victim and burrows into its flesh. They 

 seem endowed by nature with a fondness for nothing but fatty tissue, 

 which teaches them to leave the vital parts of the host alone. When 

 full-fed and ready to transform they do not, as did the last-mentioned 

 parasites, transform within the shell of the insect from which they have 

 obtained their nourishment, but perforate the skin and enter the ground 

 to the depth of from half an inch to two inches. Here they contract to 

 brown oval puparia and remain for a longer or shorter space of time. 

 According to Riley, the last brood usually winters in these puparia. 

 The following spring the fly issuing works its way to the surface of the 

 ground and takes wing. 



