THE PEAR THKIPS. 13 



surface alone is weakened, which causes the leaf to roll up until eventu- 

 ally it becomes rolled up tight (Fig. 6). In doing this the insects get 

 the tenderest part of the leaf for their food, and also secure pro- 

 tection for themselves. With such shelter no ordinary predaceous 

 insect can reach them. Often on more mature leaves the insects in 

 feeding cause a deadening of the margin and the leaf in its develop- 

 ment is forced into an abnormal, cup-shaped growth. This is a very 

 characteristic injury on pear trees (Fig. 7). 



The list of food plants of young thrips is larger than during the 

 adult stage. Aside from all the fruit trees mentioned on which the*N 

 adults feed and also on which the young are to be found, it often 

 happens that the young, by various means, are carried from the original 

 food plant to some other, being blown, for example, from the tree above to 

 a weed beneath. They have no wings and can not fly 

 back to the tree; a few crawl up again, but most of 

 them adapt themselves to the new food plant until 

 fully grown, when they go into the ground with the 

 others. All of our common weeds have thus been 

 found supporting young thrips, although no full-grown 

 insects have been seen feeding and depositing eggs on 

 such plants. 



It is the young thrips which injures fruit. Prunes^ 

 especially are affected, although a similar scab is 

 found on cherries, apricots, and pears. Well-set fruit 

 gets to be about the size of a pea before the old blos- 

 som is sloughed off, and under cover of this dead 

 blossom, on almost every prune where thrips were 

 present, one or more of the young could be found, y^^g Thrips in second 

 also a small abrasion on the skin of the fruit where larval stage, greatly 

 the insect had been feeding. We have followed this ^"^'^^s^i- ^oneumi.) 

 abrasion of the skin with the thrips present to the mature fruit with 

 its scab. Only the skin of the fruit is injured, and the marking enlarges 

 with the growth of the fruit. The scab was especially marked last year 

 where thrips were found, and it was very prevalent again this year. 

 It must be remarked, however, that something other than thrips has 

 caused much of the scab on prunes during the past year. 



During the second larval stage of the young thrips a very decided 

 change takes place. The second larva, like the first, feeds voraciously 

 and after some three weeks from the egg reaches a size often larger than 

 that of the fully matured insect. (See Fig. 8.) At this time it ceases 

 feeding and falls to the ground. We have observed but few deliberately 

 walking down the tree. Each individual goes into the ground separatel;^. 

 entering by some crack or worm hole, and having reached a secure 

 depth it hollows out for itself a little cell, and in this chamber it remains 



