2 DEClDUOCrS FRUIT INSECTS AND INSECTICIDES. 



wild plum or cherry, for its original food plant, and later, as large 

 fruit-growing districts were developed and as the insect found more 

 and ])etter food, it may have changed its feeding hahits from the wild 

 to the cultivated plants. This would be a not unusual change. On 

 the other hand, it may have been importeil and, finding conditions 

 favorable here and no efl'ective natural enemies present, may have 

 increaseil and spread rapidly. 



In 1904 the pest was thought to be strictly local in the Santa Clara 

 A'allev, but in 1905, when tlie insect had l)ecome l)etter known, it was 

 found to be widespread hi the San Francisco Bay regions and its 

 ravages were being felt in fruit sections in other than this one valley. 

 A peculiar ])ligliting of blossoms had ])een comnumly observed in 

 several localities in the Santa Clara Valley previous to 1904, and this 

 blighting was invariably followed by an almost complete failure of 

 crop. Its cause was not at first explained, for trees were injured 

 within a very few days and the insects, as it lia]ipened, were gone 

 before the owner was aware of the injury. 



The })ear thrips seems to have reached a maximum in numbers 

 diH'ing the season of 1905. Large orchard sections, often miles in 

 length, suffered an almost complete failure of croj)s and these worst 

 infested areas were in the heart of the l)est fruit sections of the valley. 

 All of this loss, however, can not be charged to the thrips, for there 

 occurred unusually heavy and driving rains during the blossoming 

 season of this year, and it was often imj^ossible to determine the 

 relative amount of injury caused by the thrips and that caused by 

 rain, except where thrips were found feeding before the storms came 

 on. The season of 1906 proved to be a more ho})eful one. Thrips, 

 fewer in numbers, were late to appear, and the early injury to buds 

 was not so apparent. The trees blossomed almost in the normal 

 way. The later injury to fruits, however, was quite as noticeable. 

 The scab on mature prunes — the never-failing evidence that thrips 

 have been feeding in the spring — depreciated the value of the fruit in 

 all of the thrips-infested regions. 



NATURE AND EXTENT OF INJURY. 



Injury to plants is the direct result of the feeding and ovipositing 

 of the thri])s. 



DKSCUirTIOX OF TMK MorTH I'AKTS. 



The mouth parts of thrips project from the lower posterior side of 

 the head and have the appearance of an inverted cone (fig. 1 ) . The 

 mouth opening is in the small distal end, and through it the stylets or 

 pien^ing organs are projected when the insect is feeding. The rim at 

 the tip is armed with several strong, chitinous points, which figure 

 prominently in tearing open the jilant tissues. The insect first pierces 



