VALUE OF A KNOWLEDGE OF ENTOMOLOGY 



15 



An excellent example of the value of parasites as insect 

 destroyers is afforded by the imported cabbage worm. One of 

 its parasites, Pteromaliis puparum (fig. 21), destroys in some 

 seasons from 80 to 90 per cent, of these "worms." Another 

 parasite, Apanteles glomeratus was purposely introduced by the 

 United States government about 1883. During the autumn of 

 1904 this species held its host under complete control in the 

 District of Columbia, killing every "worm" which came under 

 the writer's observation. This species is shown in figure 2ix. 



Fig. 2 \x.— Apanteles glomeratus. a. Adult fly; b, cocoon; c, flies escaping from cocoons 

 0, b, Highly magnified, c, natural size. (Author's illustration, U. S. Dept. Agr.) 



