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. 
Larvee feed more especially on the larger leaves and on fruits. Adults 
cause the scabbing on pears, while larvee 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 larve 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 pupe 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 larve 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. 
