12 CIRCULAR 3 4 6, U. S. DEPARTMENT OF AGRICULTURE 



Parasitized mealybugs are readily recognized by a swollen, mum- 

 mified condition. The parasite undergoes its transformations within 

 this hardened shell and finally gnaw r s its way out. Of the parasites 

 of mealybugs and scale insects, the majority of the species develop 

 singly, yet even among these some may develop to the number of 

 several dozen in a single host insect. 



PARASITES OF CATERPILLARS 



The caterpillars (larvae of butterflies and moths) and beetle and 

 sawfly larvae which feed upon the foliage of plants and those which 

 bore into the twigs and trunks of trees are attacked by a wide variety 

 of other insects. Among them are the parasitic flies, which develop 

 within the body of the host, and various wasps, which sting the 

 caterpillars and deposit their eggs either in or on the body. 



Nearly every species of caterpillar is attacked by one or more 

 species of tachinid flies, most of which bear a considerable resemblance 

 to the house fly but may be much larger. The flies of this entire 

 group, and others as well, are beneficial rather than harmful. The 

 majority of these flies lay their eggs upon the body of the caterpillar, 

 where they may be recognized as white oval spots one twenty-fifth 

 of an inch or less in length. Caterpillars may often be seen bearing 

 many of these eggs, in exceptional cases as many as 50 to 100. 

 Whether only one or many eggs are laid on a caterpillar, generally 

 only a single parasite develops to maturity, though in one instance 

 80 were reared from a single individual. 



The egg hatches within a few days after being laid, and the 

 minute maggot bores through the skin into the body. Here it feeds 

 upon the blood of the caterpillar, and after a variable period of 

 time completes its feeding upon the body contents and emerges. 

 It then enters the resting stage, usually in the soil, in a puparium 

 which is quite similar in appearance to that of the house fly and 

 the stable fly. 



The small Apanteles wasps are frequently very effective in de- 

 stroying caterpillars. The cocoons of the parasites of this group 

 are often seen upon foliage and are conspicuous because of the 

 large number that may occur in each mass and by their white or 

 yellow color. In some species the cocoons are found singly, but 

 in others they occur in clusters of from 25 to 50 or more and are 

 often covered with a loose mass of silk. These cocoons may be 

 formed directh T upon the body of the caterpillar (fig. 8) from 

 which the larvae emerged, or they may be scattered irregularly 

 about it upon a leaf, or in orderly tiers one above the other like 

 rows of bricks. An instance is recorded of more than 1,000 of these 

 parasites emerging from a single caterpillar. Many inquiries are 

 received regarding these cocoon masses, and they are often mistaken 

 for insect eggs and consequently destroyed. 



One of the most common species of this group is Apanteles glomer- 

 atus L., which attacks the imported cabbage worm {Aseia rapae L.). 

 The female wasp stings the very young caterpillars and laj 7 s from 

 15 to 50 eggs within the body. The larvae feed upon the body fluids 

 for about 2 weeks and then emerge by cutting individual holes 

 through the skin of the still-living, nearly full grown caterpillar, 

 which may not die for several days. All of the larvae contained in 



