THE PEAR THRIPS. 5 



a way down the center of the chister, feeding as it goes on the con- 

 tiguous sides of the several blossom buds. Normal growth ceases 

 immediately. The untouched outer side of each blossom ])U(l 

 develops for a time, but the injured inner part becomes brown and 

 dies. This causes each flower bud to turn in toward the center, and 

 the whole cluster eventually falls. (See PI. I, fig. 1.) When thus 

 injured, most blossoms do not open at all, but if they do thrips are 

 able to enter and feed in the more vital flower parts. Only a few 

 blossoms survive both periods of injury when thrips are very numer- 

 ous. The insects attack blossom and leaf buds alike and, in fact, 

 every part that offers new and tender plant tissue. 



Pears suffer mostly during early bud development, and blossoms 

 are nearly all dead before the clusters open. 



Cherries present a more resistant growth. There is a decidedly 

 sticky secretion on the surface of newly exposed leaves, and often 

 wings of thrips stick fast and many are thus trapped. Cherries 

 develop so rapidly that when buds once start, blossom clusters are 

 able to push out, often almost unharmed, even when many thrips are 

 present. These clusters form ideal places for oviposition, and, as will 

 be seen later, cherry trees which may be able to resist the early inju- 

 ries of feeding will suffer from the effects of ovipositing. 



Thrips have displa3'ed very decided preferences for certain flower 

 parts. It has been mentioned that they choose the inner side of the 

 almond calyx cup. In prunes they are partial to the tiny blossom 

 stems and to the tips of petals and, when blossoms have opened, to 

 the stigma and style. This last injury is especially noticeable on 

 cherries, where the writer has many times found the stigmas and 

 styles blackened as a result of the feeding of thrips, while the rest 

 of the blossoms was untouched. 



Injury on leaf buds and on tender foliage is almost as marked as 

 '"."hen blossoms alone are attacked, although there can be no closely 

 drawn line of distinction, because of the close interrelation of leaf and 

 blossom buds. Trees that have been ravaged for three or four days 

 can not again put forth new leaf buds and assume a natural growth 

 for several months, and then they appear sickly for the entire year. 

 Often they can not start anew until the thrips have actually left the 

 trees, as the insects continue to hinder each new effort which the 

 trees may make. 



The pear thrips is known to feed on the following plants, and it is 

 probable that this list, extensive as it is, is not complete: Almond, 

 apple, apricot (several varieties), cherry, fig, grape, peach (Muir and 

 Nicols' clings preferred), pear (especially Doynne du Cornice and 

 Bartlett), plum, prune, walnut (English). 



The insect shows a decided preference for certain varieties of 

 prunes, pears, and peaches, but of the other fruits all varieties seem 

 to be attacked alike. The pear thrips has been collected from the 

 27788— No. 68, pt 1—07 2 



