Chermidae 319 



but one to a leaf and only two or three upon a small plant. If disturbed the 

 nymphs may move around. 



Nymphal mortality was somewhat higher in the small than in the 

 larger cages. A high mortality often occurred at the first and second 

 molts, where conditions were for any reason unfavorable. 



Optimum conditions for egg-laying and nymphal development seem to 

 occur between 70 ° and 75 ° F., with slight temperature fluctuations. The 

 eggs, which are at the extreme end of a short stipe, are laid principally 

 upon the younger, apical potato leaves. Females have a rather long 

 oviposition period, and nymphs and adults of all stages may be had 

 by adding a new potted potato plant to the breeding cage about once or 

 twice each week. Where caged in pairs, it may be necessary to replace 

 males that die in order to maintain the fertility of the eggs. Adults 

 reared in cages appear to live longer in captivity, and to be less excitable 

 than do wild adults collected out of doors. The mortality of freshly 

 captured wild adults is sometimes heavy, especially if they are placed 

 in small cages during hot weather. 



When the nymphs become excessively abundant, it may be necessary 

 to kill or to remove part of the insects to save the plants. As many as 

 2,000 to 3,000 nymphs, in addition to adults, have occasionally been 

 found upon medium sized potato plants under both field and laboratory 

 conditions. 



Greenhouse rearings are usually successful during the fall, winter, and 

 spring months, but the psyllids have difficulty surviving during the sum- 

 mer if temperatures become excessively high. Nymphs and adults have 

 been observed to survive when the potato plants upon which they were 

 feeding were destroyed by frost. 



In order to have vigorous potato plants at all seasons of the year for 

 rearing potato psyllids, it sometimes becomes necessary, in order to induce 

 growth, to use chemicals to break the rest period upon potato tubers to 

 be used for seed. [See footnote on p. 328.] Tomato plants, and some 

 other solanaceous hosts, may be used to raise psyllids in smaller numbers. 



Biological Control. Potato psyllid colonies may be lost by allowing 

 heavy aphid infestations to develop upon and destroy the host plants. 

 Adult and larval ladybird beetles, predacious Hemiptera such as damsel 

 bugs and big-eyed bugs, lacewing fly larvae, syrphid larvae, spiders, and 

 other predators may attack laboratory colonies of psyllids, unless the 

 cages are kept free from them. No insect parasites have been noted in 

 the area under observation, but when kept under humid conditions a few 

 adults have been found which appear to have been destroyed by fungus. 



