238 MAINE AGRICULTURAL EXPERIMENT STATION. I907. 



superfluous. The efficiency of emulsion sprays for plant lice 

 has too long been known to make plausible any attempt for any 

 other direct treatment in this case. But to be successful an 

 emulsion spray since it kills by contact would need to be forced 

 under the infested leaves as well as along the tip of the stem 

 and between the buds and flowers where the plant lice are 

 particularly crowded. Just what the results of such a treat- 

 ment upon the potato might be is a problem which concerns the 

 plant pathologist, and while the fate of the insects subjected to 

 such a treatment would be satisfactory to the potato grower, 

 whether the fate of the vine would be equally so is a matter 

 which would require careful tests to decide. 



The standard remedy for plant lice, in short, seemed not 

 available for the situation in question. 



The alternative was the study of the life history of this 

 species with a view of ascertaining the alternate host plant and 

 if practicable eradicating it or controlling its growth within the 

 vicinity of potato fields. 



A Generalized Life Cycle for Nectarophora. 



In order to outline the need of such a study with a given 

 species of plant louse whose life history is not known, the life 

 cycle of plant lice in general is here briefly sketched. Although 

 the life cycle varies greatly within the range of Aphididse, the 

 family of plant lice, the following are the points drawn from 

 related forms which seemed of significance with the life cycle 

 of N. solanifolii in view. 



In the north such a plant louse may be expected to winter 

 in the egg stage. From the egg emerges in the spring a wing- 

 less form which is commonly spoken of as the stem mother. 

 The stem mother does not deposit eggs but produces living 

 young, and is the first of a long series of forms designated on 

 this account as viviparous females. The young plant lice begin 

 at once to feed upon the sap of the plant and in 8 or 10 days 

 produce offspring. The first few spring generations may be 

 wingless or at any time winged individuals or an entire winged 

 generation may appear and fly away to fresh plants and there 

 start new colonies where a succession of generations are pro- 

 duced as before. Such a winged generation is called the 



