POTATO PLANT LOUSE. 237 



favorite position is upon the peduncles of the flowers, which they cover 

 completely. They are also found in large clusters on the stems and upon 

 the under surface of the leaves. In many colonies there are a few flesh- 

 colored individuals.' 



'July 16. — The plant lice on the potatoes are fast diminishing in num- 

 bers ; but they have left the crop in a sorry condition.' 



'August 1. — I send you today a last specimen from my potato plot. 

 They have evidently been killed by a fungus. I first noticed its effects 

 about a week ago on one corner, and it has since spread over the whole 

 piece. Very few aphides are left alive. Since I last wrote, I noticed 

 larvae of lady bird beetles and of Syrphus flies ; but neither of these or 

 anything else had much effect in reducing the numbers of the plant lice 

 until this disease appeared. A month ago my potatoes could not have 

 looked more promising. Today I tried them, and out of 6 average 

 hills I got 17 tubers, of which 2 only were large enough to be marketed.' 

 — C. A. Hamilton." 



In view of so extended and injurious an infestation of one of 

 the chief crops of Maine for 3 consecutive years, it seemed 

 desirable to ascertain whether there might not be some prac- 

 tical method of treatment or prevention. The standard remedy 

 for plant lice — kerosene emulsion or whale oil soap spray — did 

 not seem advisable for several reasons. By the time the plant 

 lice have colonized the vines to an extent great enough to be 

 particularly noticeable, the damage is already half done and 

 the winged generations which develop at the time the potato 

 tops grow sickly, leave the plants they are on for fresh vege- 

 tation. The proposition of spraying 40 acres of potato vines 

 with kerosene emulsion late in August for instance when the 

 wing pads which bespeak the migrating generation are already 

 in evidence would not appeal to the large potato grower. To 

 apply such a spray before the infestation became excessive,, 

 while it would kill many of the scattered plant lice, might on 

 the other hand be a sheer waste of energy, for the amount of 

 injury which plant lice are going to inflict is a matter not fairly- 

 open to prophecy, so many elements of uncertainty enter in. 

 The weather, for instance, plays an important part in the wel- 

 fare of plant lice, heavy rains washing the tender forms from 

 the plants, and cold days retarding the rate of increase. A 

 long stretch of damp weather is favorable to fungus parasitism 

 which may sweep out the plant lice from a large area. Then, 

 too, in certain seasons, predaceous and parasitic insects appear 

 in numbers sufficient to render any artificial remedial measures 



