SEXUAL. FORMS. 77 



lens by the yellowish areas over the abdomen, due to the fact that the 

 eggs show through the body walls; also, if the males have not been 

 with them, by the manner in which they rest upon the plant, the 

 body being held at an angle of about 45° to the leaf upon which they 

 rest. In assuming this position they hold to the plant only with the 

 two first pairs of legs. Only unmated females rest upon the plant 

 in this manner. The sexes may mate once or many times, although 

 one mating is apparently sufficient to produce fertile eggs. 



One agamic female may produce all agamic individuals, a com- 

 bination of agamic males and oviparous females, or only true females 

 and males. When only the latter, it seems that the females far 

 outnumber the males. 



Mr. C. N. Ainslie, in 1908, in Washington, D. C, records a very 

 singular phenomenon. On April 4 of that year he observed males, 

 oviparous females, and eggs of Toxoptera in his cages in the office. 

 A number of eggs were obtained, but none of them would hatch. The 

 source of this material, however, is somewhat obscure. Mr. Kelly 

 had sent in material from Leavenworth, Kans., previous to these 

 finds and this was kept breeding in the office, together with material 

 collected locally. The junior author also found an adult male in his 

 rearing cages in the insect ary at Washington during April, 1911. 

 This apparently developed from material that had been kept breed- 

 ing all winter. 



DESCRIPTIONS. 



Since in the earlier stages the young can not be distinguished from 

 those of the summer forms, it is unnecessary to go into detail with 

 reference to them. The males may probably be identified in the 

 third instar by their small size; they are much smaller and the abdo- 

 men more pointed, posteriorly, than the summer forms of this stage 

 that later will become winged. Those young that will develop into 

 oviparous females can not be determined with any degree of accuracy 

 until the fourth instar. They are usually a little paler in color, and, 

 instead of embryos, light yellowish ova can be seen, with a hand 

 lens, developing within the body (see fig. 9). The description of 

 the male and female first appeared in the Canadian Entomologist, 

 in an article on " Sexual Forms of Toxoptera graminum, Rond," by 

 Prof. F. L. Washburn. 1 His description is as follows: 



Oviparous female. — Length, 2-2.25 mm.; color, yellowish green, median line of 

 abdomen darker green; head and prothorax somewhat paler than the rest of the body. 

 Eyes black; antennae black, except the two basal joints, and the basal half of the 

 third, which are the same color as the head. Legs yellowish, tibia brownish toward 

 the apex, tarsi black; cornicles greenish, their apex black; cauda greenish. Antennae 

 slender, hardly one-half the length of the body, no circular sensoria. Cornicles 

 slightly tapering, not reaching to the end of the body. Cauda slender, somewhat 



i Can. Ent., vol. 40, No. 2, February, 1908. 



