246 NEW YORK STATE MfSEL'M 



of l)actLTial er other diseases. In otluT specit-s oi plant lice this protective 

 device is carried tn an excn t^rcatcr extent, and the whitish powdery 

 matter is secreted cupit)usly fronA more highly developed glands as long 

 woolly filaments. .Such ])rotcction is v(!ry common and one has only to 

 refer to such species as the woolly a])plr aphid, S c h i z o n e u ra Ian i- 

 g e r a Hausni., the woolly alder a])hid, V e 111 \> h i g u s t e s e 1 1 a t a Fitch, 

 fre([uentl\' known as alder bligiu, and also in tht' case of such leaf-feeding 

 species as the beech leaf aphid, Phy 11 aphis fagi Linn. This wooll\- 

 matter undoubtedly affords consitleralile ])r<)tection 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 eas\ tor the insect to frighten away the small parasite and the 

 presence of the woolly fdanieius 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 j)rotective value these fila- 

 ments possess, since it is ver\' dithcult to kill such plant lice b)' the applica- 

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

 illustrate different protective devices and among these we may include the 

 leaf curlers. It is a wc^ll known fact that nn)st 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 immenselv 

 increased whenever thi? insects are abunilant enougli so that their attack 

 results in more or less irregular curling of tlu- leaxcs. This curling is the 

 mechanical result of the abstraction ot lluids from the underside of the leaf 

 and is verv markeil in attacks b\- the common cherry ajihid, Myzus 

 cerasi b'abr., where the leaves are fn-(|uently so deformed that it is almost 

 impossible to hit the insects within with an\- kind of a spra\'. .\phids are 

 almost invarialjK' more abundant near the center of the curled leaf where 

 [jrotection is most perfect. This ciu'ling affords shelter from inclement 

 weather and ijrobal)ly wards off, to a considerable extent, attacks of jjara- 

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

 instances and we may have, as in the case of a species, 1 1 a ni am e I i s t e -- 



