246 NEW YORK STATE MUSEUM 



of bacterial or other diseases. In other species of plant lice this protective 

 device is carried to an even greater extent, and the whitish powdery 

 matter is secreted copiously from more highly developed glands as long 

 woolly filaments. Such protection is very common and one has only to 

 refer to such species as the woolly apple aphid, Schizoneura 1 a n i- 

 gera Hausm., the woolly alder aphid, Pemphigus te sella ta Fitch, 

 frequently known as alder blight, and also in the case of such leaf-feeding 

 species as the beech leaf aphid, Phy 11 aphis fagi Linn. This woolly 

 matter undoubtedly affords considerable protection from inclement weather 

 and also from parasites and predaceous enemies. The unprotected parts of 

 the plant louse are those near the legs or head where it would be compara- 

 tively easy for the insect to frighten away the small parasite and the 

 presence of the woolly filaments probably renders its bearer distasteful to 

 such predaceous forms as the lady beetles or their young. The economic 

 or practical entomologist is well aware of the protective value these fila- 

 ments possess, since it is very difficult to kill such plant lice by the applica- 

 tion of ordinary contact insecticides. There are many other species which 

 illustrate different protective devices and among these we may include the 

 leaf curlers. It is a well known fact that most of our species of plant lice 

 feed to a considerable extent upon the underside of the leaves where they 

 are largely protected from inclement weather and this shelter is immensely 

 increased whenever the insects are abundant enough so that their attack 

 results in more or less irregular curling of the leaves. This curling is the 

 mechanical result of the abstraction of fluids from the underside of the leaf 

 and is very marked in attacks by the common cherry aphid, Myzus 

 cerasi Fabr., where the leaves are frequently so deformed that it is almost 

 impossible to hit the insects within with any kind of a spray. Aphids are 

 almost invariabl)- more abundant near the center of the curled leaf where 

 protection is most perfect. This curling affords shelter from inclement 

 weather and probably wards off, to a considerable extent, attacks of para- 

 sitic and predaceous insects. Leaf curling is carried further in some 

 instances and we may have, as in the case of a species, Hamamelistes 



