109 



PREDACEOUS ENEMIES OF THE LARGER LARV^ AND MOTHS. 



Foremost among the predaceous enemies of the boll worm are several 

 species of Polistes. There are three species which frequent the cotton 

 fields: P. annularis Linn., a large black form with black wings and a 

 single black cross band of yellow near the base of the abdomen; F. 

 riibiginosiis Lepel., a large, slightly stouter, rust-red species, with dark 

 wings; and P. texanus Cress., a smaller, more slender, and variably 

 striped form with paler wings. Polistes annularis builds large nests, 

 often nearly a foot in diameter (see PL XVIII, fig. 1), and sometimes 

 containing upward of a thousand cells; the others construct smaller 

 nests, generall}^ from 3 to 6 inches in diameter, and containing a pro- 

 portionately smaller number of cells. 



Fig. IG.—Chrysopa oculata: adults, eggs, larvse, and cocoon (from Marlatt). 



The adults of Polistes pass the winter hibernating in protected places 

 near the cotton fields, and early in the spring each female starts a new 

 nest. The larvae of the wasps are fed upon chewed-up bits of caterpillars 

 captured by the wasps. By the middle of the summer, when the bollworm 

 is attacking cotton, their colonies are well grown and vast numbers 

 of the wasps are circulating through the cotton fields in their tireless 

 search for caterpillars. Once a bollworm is discovered, the Polistes 

 seizes it just back of the head with her mandibles and in the case of 

 a large worm usuall}^ stings it to death. Then, after a preliminary 

 chewing, she carries it off to the nest, where it is distributed and fed 

 to the wasp grubs. All cotton fields are well supplied with the wasps. 



