THE PEAR THRIPS IN CALIFORNIA. 13 



is very noticeable when the fruit is picked in the fall. Although at 

 this time the insects in question have been in the ground three or 

 four months, the injury becomes more apparent with the maturity 

 of the fruit, and the scabbing or scarring shows as the result of the 

 early spring feeding by this species. 



The most serious injury to deciduous fruits by the pear thrips is 

 caused, first, by the feeding of the adults; secondly, by the feeding 

 of the larvae, and thirdly, by the deposition of eggs in the plant tissue 

 by the adults. The effect of this last injury is more apparent upon 

 the fruits of prunes and cherries than upon the other deciduous 

 fruits. Numerous cases have been observed by the writers in both 

 prune and cherry orchards where the trees blossomed heavily and 

 there was promise of the setting of a good crop of fruit, but where 

 practically all the fruit dropped, solely from the effect of having too 

 many eggs deposited in the fruit stems, thus weakening the tissues, 

 and because the larvae, feeding directly on the fruit and foliage, so 

 weakened the tree that it would not support a heavy crop of fruit. 

 Perhaps the chief injury to cherries is caused by the deposition of 

 eggs in the fruit stems. The long and tender stem of the cherry 

 presents a most favorable place for the deposition of a great number 

 of eggs. 



Injury to the various fruits by adults and larvae is different, but, 

 classed in regard to bud structure, those fruits in which only a single 

 blossom is produced in a fruit bud, such as the almond, apricot, and 

 peach, seem to be less liable to severe injury than are the fruits which 

 which form a cluster of blossoms amd later produce a cluster of 

 fruits, such as pear, prune, cherry, and apple. If the thrips had 

 their choice of food plants, pears would probably be attacked first 

 in the spring and destroyed; also, other things being equal, a given 

 number of thrips would do more injury no doubt in a pear orchard 

 than in a cherry or prune orchard. 



INJURY TO PEARS. 



The greater injury to pears is caused by the feeding of the adults 

 in the bud clusters before blooming. Coming out of the ground in 

 great numbers in the spring as the fruit buds are swelling, the thrips 

 soon work their way underneath the bud scales and there attack the 

 individual buds. The feeding is not a biting and chewing process, 

 but the thrips, by rasping the tender surfaces in the developing buds 

 with their hardened or chitinous mouthparts, rupture the skin, and 

 the exudation of sap begins. If only a few thrips are present this 

 injury may be slight and the buds may develop and bloom, producing 

 fruit of normal size, although sometimes short-stemmed, or scarred 

 and misshapen. (See PI. II, fig. 1.) Plate II, figure 2, shows two 

 Bartlett pears which grew from a cluster that was badly injured but 



