2 DECIDUOUS 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 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 
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 happened, were gone 
before the owner was aware of the infury. 
The pear thrips seems to have reached a maximum in numbers 
during the season of 1905. Large orchard sections, often miles in 
length, suffered 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 year, 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 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 thrips. 
DESCRIPTION OF THE MOUTH PARTS. 
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 
ee a 
Pied 
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 
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