6 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 



following indigenous plants: Blossoms of the madrona {Arbutus 

 menziesii) and wild California lilac (CeanotJius thyrsiJJorus), and foli- 

 age of poison oak (Rhus diversUoha). All of these plants, however, 

 were near thrips-infested orchards, and, moreover, only a few indi- 

 viduals were taken from each of the plants. 



FEEDING HABITS OF I.ARV.E. 



Thi-ips larvae feed almost entirely on young, tender foliage and on 

 the surface of fruits. The}" conceal themselves in terminal buds (PL 

 I, fig. 2), and often, as on the cherry, they attack the underside of 

 leaves, usually near the prominent veins. They cause the leaves to 

 become much contorted, ragged, and full of holes (PI. II, fig. 1). The 

 insects seem at times to take advantage of certain tendencies in the 

 growth of plants on which they happen to feed. For example, 

 newly opening pear or apple leaves show a tendency to roll from the 

 sides inward and thrips find this inner protected surface a most 

 desirable feeding place. In such a case the upper, inner surface is 

 destroyed, and the leaf, instead of opening out, 

 becomes rolled up tight and eventually dies. The 

 insect thus secures the tenderest of leaf tissue for 

 its food, and also protection in the folded leaf. 

 (PI. I, fig. 2.) Thrips often cause a deadening 

 of the leaf margin, and in such cases the leaf is 

 forced into an abnormal, often cup-shaped, growth. 



Fig. 2.— Eggs of the pear _,, . . , .... 



thrips {Euthrips pyri). This IS a vciy characteristic injury on pear trees. 



Highly magnified (orig- (PI. I, fig. 3 ) The feeding injury of thi-ips larvae 

 on fruits, especially prunes, is in a way superficial, 

 but it seriously impairs the appearance of the ripened fruits and 

 greatly lessens the value of the finished product. A prune grows 

 to be larger than a grain of wheat before the dead calyx is sloughed 

 off. Larvae feed under protection of this dead calyx, and as a 

 result an abrasion of the skin, the feeding injury, is noticeable, even 

 on ver}^ small fruits. The wound appears first as a small brown 

 spot which enlarges and produces a scab as the fruit matures. The 

 seriousness of what at first might seem a small surface marking 

 is more readily appreciated when one recalls that when primes are 

 being cured the tough, scabby spot does not shrivel up during the 

 process of drying as does the flesh of the prune, nor does it assume 

 a darker color as does the prune. 



Thrips larviP are often carried by various means from the original 

 food plant to other hosts, being blown, for example, from a tree to 

 grass or weeds beneath. They have no wings and can not fly back to 

 the tree. A few crawl up again, but most larva) adapt themselves to 

 the new plant until fully grown, when they, too, go into the ground. 

 Man}^ of the common weeds have thus been found supporting larvae, 

 although no full-grown thrips have ever been seen feeding or deposit- 



