6 DECIDUOUS FRUIT INSECTS AND INSECTICIDES. 
following indigenous plants: Blossoms of the madrofia (Arbutus 
menzieswv) and wild California lilac (Ceanothus thyrsiflorus), and foli- 
age of poison oak (Rhus diversiloba). 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 LARVE. 
1 Thrips larvee feed almost entirely on young, tender foliage and on 
i the surface of fruits. They conceal themselves in terminal buds (PI. 
| 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 (Pl. 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. 
(Pl. 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. 
ee eee Ow te De’ This is a very characteristic injury on pear trees. 
thrips (Euthrips pyri). yi jury p 
Se Oia corig- (Pl.1,fig.3.) The feeding injury of thrips larve 
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. Larve feed under protection of this dead calyx, and asa 
result an abrasion of the skin, the feeding injury, is noticeable, even 
on very 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 
I] is more readily appreciated when one recalls that when prunes 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 larve 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 larve adapt themselves to” 
the new plant until fully grown, when they, too, go into the ground. 
Many of the common weeds have thus been found supporting larve, 
although no full-grown thrips have ever been seen feeding or deposit- _| 
