THE DOCK FALSE-WORM. 7 



not to be considered. The apple foliage is so much tougher and 

 dryer than the succulent foliage of the moisture-loving plants upon 

 which they are accustomed to feed that the change of food plants 

 would be practically impossible. 



This insect becomes of economic importance, then, only in orchards 

 in which its ordinary food plants are growing, and such orchards 

 would naturally be those that, either through carelessness or because 

 of sod or a cover crop, are not kept clean cultivated. Any orchard 

 kept moist enough to support a cover crop is a favorable place for 

 the food plants of the insect to grow, and since these food plants are 

 widespread, the chances of some one of them, at least, getting into 

 the orchard are very good. 



From the description of the injury to apples given above it will be 

 seen that individually this insect is fully as injurious to the fruit as 

 the codling moth, for a single larva will often bore several holes in 

 one apple, and sometimes in several apples, before forming its final 

 burrow. This burrow, too, is often larger than that made by the 

 codling-moth larva and is confined to the flesh of the apple. The 

 tendency of these apples to rot seems to be greater than that of ordi- 

 nary wormy apples. Collectively, these larvae have never proved as 

 destructive as many other insects, because they have not been as 

 numerous. It is not inconceivable, however, that they might, under 

 favorable conditions, become a more serious pest. 



In the Entiat Valley, Washington, where this insect was chiefly 

 studied, there was a large quantity of wild buckwheat or bindweed 

 {Polygonum convolvulus) in the infested orchards, growing in the 

 alfalfa cover crop, and this often was climbing up into the trees for 

 some distance. It can thus be readily seen how the larvae found their 

 way into the trees and to the fruit. The Jonathan variety was the 

 worst infested, since the tree is of a drooping habit, and the many 

 heavily laden branches, extending down into the alfalfa, afforded the 

 larvae an easy opportunity to reach the fruit. In the fall of 1914 the 

 extent of injury in one orchard was estimated at about 2 per cent. In 

 1915 actual counts were made from four representative trees in this 

 orchard, and it was proved that more than 5 per cent of the picked 

 fruit was rendered unmarketable by this worm. This would represent 

 a loss in this particular case of about 16 cents per tree, since the value 

 of the fruit from these trees, which were only 7 or 8 years old, was 

 something over $3 per tree. This was in spite of the fact that 

 the larvae had been heavily parasitized the preceding spring. The 

 loss may at times be considerably higher, and, in fact, as already 

 noted, Prof. Melander has written of injuries running as high as 10 

 per cent. 



