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MANUAL OF AMERICAN GRAPE-GROWING 



but is especially destructive to grapes with tender skins and 

 such as grow in compact bunches. Its work is detected usually 

 in compact grape clusters where a number of berries are injured 

 by a "worm." The "worm" is a dark-colored caterpillar, the 

 larva of the grape-berry moth (Polychrosis viteana.) There 



are two broods of this cater- 

 pillar, the first of which feeds on 

 the stems and external portions 

 of the young berries, while the 

 second attacks the berries. The 

 loss to the fruit-grower is of two 

 kinds, the loss of the fruit and the 

 marring of clusters which entails 

 the cost of picking out worthless 

 berries. Figure 43 shows the work 

 of the grape-berry moth. The 

 damage is usually greatest near 

 woodlands since the trees cause 

 more snow to lodge in the adjoin- 

 ing vineyards, this protection per- 

 mitting a greater percentage of 

 pupae to survive. 



The moth passes the winter in 

 the pupal state on leaves under- 

 neath the vine, emerging about 

 the time grapes are blossoming. 

 The sexes then mate and the eggs 

 are laid on the stems, blossom clusters and newly set fruit. 

 After reaching full growth, the caterpillars cut out a portion 

 of the leaf from which they make a pupal case by means of 

 silken threads, and here pupate for the second brood which 

 emerges in late July and August. Eggs are laid at once and 

 from these come the caterpillars which live entirely in the 

 berry. The larvae leave the berries about the time the fruit is 



FIG. 43. A "bunch of grapes 

 despoiled by the grape-berry moth. 



