66 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



insure their destruction. Small areas containing thrips have been 

 submerged as long as seventy-two hours, and when examined a few 

 days later all thrips were alive and active. 



SUMMARY. 



The pear thrips has been found only in localities in the general region 

 of San Francisco Bay. Its presence in other countries is not known. 



The adults accomplish their feeding injury by rasping the tissues 

 and sucking out the plant juices in the early buds and blossoms. 

 Larvae feed more especially on the larger leaves and on fruits. Adults 

 cause the scabbing on pears, while larvae produce the scabbing on 

 prunes. 



Adults emerge from the ground in late February and early March, 

 just when most trees are spreading their buds and opening into bloom. 

 Eggs are placed mostly in the blossom and fruit stems and in leaf 

 petioles. The larvae hatching therefrom feed for two or three weeks, 

 then drop to the ground, where they form a tiny protecting cell 

 within which they remain during the rest of the year. The pupal 

 changes take place within this cell in the ground during October, 

 November, and December. 



To gain complete control of the pear thrips, both plowing and 

 spraying should be adopted as remedial. Land should be plowed as 

 soon as possible after the early rains in October, November, and 

 December, to a depth of from 7 to 10 inches, harrowed or disked, 

 and then cross plowed, the second plowing to be followed also by 

 harrowing. The pupae are by this means broken from their pro- 

 tecting cells and most of them either injured or killed. 



A combination spray of black-leaf tobacco extract in the propor- 

 tion of 1 part of extract to 60 parts of water and 2 per cent distil- 

 late-oil emulsion, or a spray of black-leaf extract alone, should be 

 used against the adults during early March, just when the cluster 

 buds begin to open, and against the larvae in April, after the blossom 

 petals fall. The thrips must be killed by contact insecticides, and 

 not by internal poisons. 



Fertilizers and irrigation do not kill the thrips in the ground. 

 They act against them only indirectly, by placing the soil in better 

 condition for cultivation and by strengthening the trees. 



