THE PEAK THRIPS AND ITS CONTROL. 



55 



The period of blossoming for similar varieties in Contra Costa 

 County is about the same as that in the Santa Clara Valley, while the 

 orchards in the Vaca and Suisun valleys and along the Sacramento 

 River may be a very few days earlier. 



INJURY TO TREES BY OVIPOSITION. 



The adult female is equipped with a pointed and curved, sawlike 

 ovipositor (fig. 13), by means of which deep cuts are made, into which 

 the eggs are placed well down into the tissues of the plants, mostly 

 in the stems of blossoms or leaves or into the leaf tissue. A single 

 incision is minute and in itself does little harm, as the wound soon 

 heals over, but the tiny stems of the blossoms or of newly setting 

 fruits and the leaf petioles are unfortunately preferred by the insect 

 for ovipositing situations, so that many incisions are often cut into a 

 single stem, which, becoming greatly 

 weakened, turns yellow and the fruit 

 falls. This injury becomes very notice- 

 able at times on the prune and cherry 

 and is undoubtedly the cause of much 

 dropping of immature fruit. 



INJURY BY LARV^. 



Fig. 13.— The pear thrips (Euthrips 

 pyri): Ovipositor and end of abdomen 

 from side. Much enlarged. (Author's illus- 

 tration.) 



Thrips larvse are wingless, never of 

 their own accord traveling from the 

 host plant on which they are born, and 

 usually do not move far from the im- 

 mediate locality where they have issued 

 from the egg. They seek some sheltered place within a cluster of 

 leaves, in blossoms, or under the protection of the drying calices of 

 such fruits as prunes or cherries. Larvse are found mostly during the 

 last of March and in April and their injury is distinctly on leaves and 

 fruits and not in opening buds. To them must be attributed almost 

 all the scabbing on prunes (PL VI, figs. 2, 3), some silvering on apri- 

 cots and peaches, and most of the deformed, ragged, and partly dead 

 leaves. This injury to the foliage greatly stunts and weakens a tree 

 if it is repeated during several successive years. 



SEASONAL HISTORY AND HABITS. 



APPEARANCE OF ADULTS FROM SOIL IN SPRING. 



The following table shows clearly just when the first adult thrips 

 are leaving the ground, when in maximum numbers, and when the 

 last individuals are appearing. The figures here represent the total 

 number of thrips collected from four cages from each of four orchards 



30490°— Bull. 80—12 5 



