THE SCALE PARASITE 



347 



ing about a week or two after the first, in order to make 

 sure that all young worms will be poisoned. 



Infested apples frequently fall to the ground. Up to a 

 certain point this enables the remaining ones to increase in 

 size, on, the principle that the falling is a thinning out process. 

 Since nearly all the early falling apples are apt to be wormy, 

 they should be gathered promptly and fed to the hogs. 



ICHNEUMON FLIES. 



These are beneficial, as they lay their eggs in harmful caterpillars. 

 The eggs hatch and the maggots kill the caterpillars. 



254. A Few Helpful Insects. If the farmer were obliged, 

 by himself, to check the ravages of each particular pest, 

 it would probably soon be impossible for him to raise 

 enough food for the world's needs. Fortunately for us, 

 insects are ever waging a bitter warfare among themselves. 

 The moment the numbers of one kind increase above the 

 normal, they are preyed upon and checked by parasites. 



255. The Scale Parasite. A notable example of this 

 warfare by parasites is seen in the gradual decline in the 

 numbers of the San Jose scale. But a few years ago the 

 scale seemed to be destroying nearly every unsprayed 



