480 



Saw-flies, Gall-flies, Ichneumons, 



For example, the American tent-caterpillar has been found by Fiske (New 

 Hampshire) to be attacked by twelve species. 



With regard to the number of parasitic individuals that may live at the 

 expense of a single host individual no generalization can be made; the 



FIG. 676. Hymenopterous parasites of a social-wasp. Fig. i, nest of Vespa sp., portion 

 of two envelopes cut away (two-thirds natural size); fig. 5, an adult parasite, 

 Sphecophagus (?) predator, female; fig. 6, male of same species; fig. 10, Melittobia 

 sp., female. (After Zabriskie; natural size indicated by lines.) 



number varies, Howard says, from i to 3000. From a single caterpillar 

 of the cabbage-moth, Plusia brassica, 2500 individuals of the parasite Copi- 

 dosoma truncatellum have been bred. From large hosts are often bred 

 large numbers of parasites, but with some parasitic species only one or a few 

 eggs are ever laid on a single host, whether it be large or small. Small hosts 

 cannot, of course, provide food for many parasites and hence the number in 



