112 Bulletin 223. 



In some badly infested vineyards we found many clusters with over 

 three-fourths of the berries infested. Oftentimes the caterpillar goes 

 from one berry to another, fastening them together with a few silken 

 threads. To determine how many berries one caterpillar usually 

 spoils, we put in our cages on July 30, two clusters each containing 

 17 grapes infested by young caterpillars; by August 15, there were 

 25 and 29 "wormy" grapes in the clusters. This experiment and 

 other observations indicate that one caterpillar rarely destroys more 

 than two green grapes in summer, and one berry often furnishes 

 sufficient food. Every infested berry helps to spoil the symmetry 

 of the clusters and necessitates the labor of removing such berries 

 before marketing the crop, except where they can be sold cheap for 

 wine. Several vineyardists have demonstrated the practicability 

 of picking off the infested green berries when they are conspicuous 

 in August. 



When the summer brood of caterpillars get full-grown in August, 

 they all go onto the leaves and cut out their characteristic cocoons, as 

 shown in Fig 22. In our cages the caterpillars would wait for several 

 days and sometimes die before transforming, if leaves were not sup- 

 plied them for cocoon-making.* 



A partial third brood in autumn. — By August 1, many of the cater- 

 pillars of the second brood have changed to pupae in their cocoons on 

 the leaves. In from 12 to 14 days the pupae transform and the moths 

 emerge. We reared many moths from August 15 to 20 and most of 

 them emerged in the forenoon, but all came from cocoons made before 

 August 15. It seems that all caterpillars of the summer brood which 

 pupate after about the middle August do not transform to the moth 

 state that year. In other words, part of the second brood of pupae 

 hibernate, and part develop into moths to produce a partial third or 

 autumn brood of caterpillars which work in the ripening grapes. This 

 third brood is not nearly so large as the second, and as many of the 

 fruits infested by the latter drop off before the fruit ripens, oftentimes 

 the infestation does not seem as bad at picking time as in August, 

 but the clusters are more ragged.. Most of the caterpillars are full- 

 grown before October 1, but some were found working in very ripe 

 fruit two weeks later. A few caterpillars transform in autumn to 

 pupae inside the berries they infest, but most of them make their 



*The pupae are 5 millimeters (yV inch) in length and of a light greenish-brown 

 color, with eyes and caudal border of abdominal segments and last two or three 

 segments darker brown. There is a row of coarse, short spines near the cephalic 

 border, and a row of finer ones along the caudal border of the dorsum of each 

 abdominal segment; and eight bristles with recurved tips for hooking into the 

 silken cocoon occur around the tip of the abdomen. 



