2 DECIDUOUS^ FRUIT INSECTS AND INSECTICIDES. 



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

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

 and better food, it may have changed its feeding habits from the wild 

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

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

 favorable here and no effective natural enemies present, may have 

 increased and spread rapidly. 



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

 Valley, but in 1905, when the insect had become better known, it was 

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

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

 A peculiar blighting of blossoms had been commonly observed in 

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

 l:)ligliting 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 happened, were gone 

 before the owner was aware of the injury. 



The pear thrips seems to have reached a maximum in numbers 

 during the season of 1905. Large orchard sections, often miles in 

 length, suflered an almost complete failure of crops and these worst 

 infested areas were in the heart of the best 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 3"ear, and it was often impossible 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 hopeful one. Thrips, 

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

 was not so apparent. The trees l)lossomed almost in the normal 

 way. The later injury to fruits, however, was ([uite 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 regicms. 



NATURE AND EXTENT OF INJURY. 



Injury to ])hints is the direct result of the feeding and ovipositing 

 of the thri})s. 



DESCRIPTION OF TUE MOITTU PARTS. 



The mouth })arts of thrips ])roject from the lower ]K)sterior 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 

 piercing 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 plant tissues. The insect first pierces 



