32 



and there remains until the parasite emerges. The grub of the 

 Adialytus is yellowish white, thick-bodied and short. It lies bent 

 upon itself and when removed is perfectly helpless. The pupae lies 

 in the same position, is also white, with the large eyes showing 

 conspicuously at the sides of the head. The adult emerges within 

 the dried skin of the louse it has inhabited and at once gnaws 

 a round piece out of the back of the latter, generally near the pos- 

 terior end of the body, and pushing this piece out emerges through 

 the opening made. Often these pieces which are gnawed out adhere 

 at one side, so that after the parasite has emerged they fall back 

 in place and the empty skin looks much as before. The parasites 

 emerge in great numbers in the fall of the year at the time the 

 winged females become most abundant, and I believe many of them 

 hibernate as adults. An examination of a great number of swollen 

 plant lice in midwinter, however, reveals a few with living grubs. 

 Lice that are infested with this parasite seem never to produce 

 young, their whole existence being given up to bringing the unwel- 

 come guests to maturity. The wingless females seem to suffer most 

 from its attacks, by far the greater number of swollen bodies repre- 

 senting this form, but a good many pupte and winged females also 

 become infested. The greater immunity of the winged louse is prob- 

 ably due to its greater activity ; when disturbed, in warm weather, 

 it takes wing readily. 



Syrphus Fly Larvce. — Next to the small hymenopterous insect just 

 described, the larvae of small dipterous insects known everywhere as 

 syrphus flies are most destructive of the lice. These larvae are con- 

 siderably larger than their prey, and spend their time creeping 

 about among the herrls of lice on the corn ears and tassels. They 

 seize the plant lice in their mouths, and in a few minutes have 

 sucked out all their juices. Great numbers of lice are destroyed by 

 a single larva in the course of a day, as they are very active and 

 voracious. They occur throughout the summer months, and are 

 sometimes found as late as November. Their empty pupa skins are 

 sometimes found with a round hole in the posterior part, from which 

 some parasite, has emerged. 



The Syrphus fly larva is elongate cylindrical, transversely wrinkled 

 with a blunt posterior end, tapering more nearly to a point anter- 

 iorly. The head is not much different from the other body seg- 

 ments. On each side of the mouth is a black, hard, toothed jaw, 

 which serves to hold the lice. There are no eyes. The color is pale 

 green when the alimentary canal is filled with the juices of plant 

 lice ; at other times it is yellowish brown. Its length is about three- 

 tenths of an inch. 



The adult is a handsome two-winged fly, with large reddish brown 

 eyes, transparent iridescent wings, shining, greenish black thorax, 

 and with the abdomen alternately striped transversely with black 

 and yellow. The head is chiefly yellow, with a frontal tuft of short, 

 dark pubescence, and a wide black band extending down the front 

 to near the base of the antennae, with silvery pubescence behind the 

 eyes. The three basal articles of the antennae are orange yellow ; 

 the bristle is black. A wide yellow stripe extends from the anterior 

 margin of the thorax on each side to the bases of the wings, where 



