July 9, 1917 Study of Eriosoma pyricola 67 



agree in structure with any of the known species, including E. lanuginosa 

 Hartig. It was pointed out, however, that the woolly pear aphis was 

 very close in general structure to European specimens of E. lanuginosa. 

 This was shown in the following words (2, p. 358) : 



The winged forms of E. pyricola are remarkably like those of E. lanuginosa Hartio-. 

 The proportions are almost exactly the same. 



The marked difference in the wax pores and minor diflferences in the 

 sensoria were considered as showing a very distinct species. The present 

 studies have shown that these characters are not the same in the spring 

 forms living on elms as in the summer and fall forms living on pear roots, 

 but that in the spring forms they are very similar to those of E. lanuginosa. 

 From the fact that in other species of Eriosoma the wax pores are con- 

 stant the writers concluded that they would be constant also in the E. 

 pyricola and in E. lanuginosa. They are not so in E. pyricola. Lack of 

 fall material of E. lanuginosa makes it impossible to determine whether 

 they are constant in that species or not. From the very great similarity 

 between the spring forms of E. pyricola and E. lanuginosa the writers are 

 led to believe that the same variation will be found between the spring 

 and fall forms of E. lanuginosa. If this proves true, there will no longer 

 be any reason for keeping the two species distinct and E. pyricola will 

 become a synonym of E. lanuginosa. 



If this supposition is correct, and it is all but proved, it will show 

 without a doubt the following to be facts: 



(i) The destructive woolly pear aphis of this country is a European 

 insect imported into the Western States on pear stock. 



(2) It has spread rapidly in the West in the last 25 years and now 

 occurs from Washington to California, although as yet it is most de- 

 structively abundant in California. 



(3) The isolated infestations in the Middle West and in the East are 

 due to separate infested importations. 



(4) While the alternate winter forms thrive best on European elms, 

 the species is able to live successfully upon the common American elm 

 and at no very distant date may become entirely adapted to this native 

 tree. 



(5) The species is liable through importarions to gain a foothold in any 

 pear-growing region, for, as recently as 1916, skins have been collected on 

 seedling nursery stock. 



DESCRIPTION OF ERIOSOMA PYRICOLA 



Stem mother. — Antennal segments with the following measurements: I, 0.048 mm. ; 

 11,0.064 mm.; Ill, 0.208 mm.; IV, 0.112 mm.; V, 0.05 mm. Segment IV of antenna 

 fully imbricated and armed with rather prominent hairs. Segment V fits close against 

 segment IV, with little constriction, so that it does not give the general appearance of 

 a distinct segment, although this is easily observable when looked for. The unguis 

 comprises somewhat more than half of the segment. Form of body globose. Length 



