Junes. i9i6 Woolly Pear Aphis 355 



it may be that the environment and conditions hastened it. Under favor- 

 able conditions of soil the migrants were produced in great abundance on 

 both young and old pear trees. In many cases, especially on young trees, 

 it appeared that fully 90 per cent of the aphides observ'ed at one time were 

 pupse, and in other instances observations in October and later after the 

 winged forms had departed indicated that almost the entire infestation 

 had developed into migrants. On old trees there remained on the average 

 a larger residue of wingless forms. On unfavorable types of soil the 

 winged forms are produced in far less abundance. It appears to be a 

 rule that the heavier and drier the soil the larger the percentage of pupse 

 developing. It sometimes happens that the migrants are unable to rise 

 to the surface of the ground and become imprisoned in pockets in the soil. 

 In one instance two living sexual females were found in such a pocket 

 beside dead migrants. 



The winged forms have been noticed on pear foliage and on the trunk, 

 but with one exception ^ no deposition of sexes has been obser\^ed on the 

 pear. On cork and American elms (Ulmus spp.) migrants were ob- 

 ser\'ed to deposit the sexes in cracks in the bark and on the lower surface 

 of leaves. In one instance the migration from a nursery of pear trees to 

 a group of young elms 200 yards distant could be traced. The migrants 

 fly readily and strongly and are stimulated by the sun's rays, being more 

 active on warm than on cool days. On the elms they were more abun- 

 dant on trees with rough bark than on the smooth-barked plants. 



The migrants vary considerably in size. They are rather elongate, 

 shining black or dark green, with a tuft of white v/ool on the caudal seg- 

 ment; otherwise, there is no flocculence. The lower surface is dark 

 green, sparsely pov\'dered at the sutures. The antennse, eyes, and a por- 

 tion of the legs are black. The base of the femora and the middle por- 

 tion of the tibice are yellowish brown or amber. The wings have narrow 

 black veins and a greenish blue stigma. The wing insertions are some- 

 times brown, but are more often yellowish. In recently molted indi- 

 viduals there is sometimes a smoky-brown patch at the base of the fore 

 wings. 



To obtain the sexes, migrants vrere confined in stender dishes and in 

 small rubber cells mounted on microscope slides with cover glasses as 

 lids. Some were kept in a lighted room in which the temperature varied 

 very considerably, at times rising to 75° and at other times falling to 

 55° F. Others were kept in a dark cellar' where the temperature varied 

 but little and averaged about 61° F. Under cellar conditions the 

 migrants deposited more sexual forms than under the conditions ob- 

 taining in the room. Some of the dishes were kept dry and others 

 moistened to different degrees. In the moistened dishes the sex pro- 



' In August, 191 1, at San Jose, Cal., a migrant was noticed depositing sexes on the upper surface of a pear 

 leaf. 



