524 U. S. NATIONAL MUSEUM BULLETIN 216 taut 3 



proof that the two forms are either the same species or two different 

 species is still lacking. We consider them the same because : 



1. The morphological and color differences between the two 



forms are more quantitative than qualitative, and are rather 

 variable, with no really absolute differences. 



2. Both forms have the same geographic range, same hosts, and 



are usually reared from the same host cells. 



3. The two forms have similar color races or subspecies in the 



different parts of their ranges. 



4. The "summer form" is not known to overwinter. 

 Considering the two forms as the same species, and piecing together 



the published information and what can be deduced from museum 

 specimens, the biology appears to be as follows: Overwintering is as 

 larvae, pupae, or adults in tough, angular, ribbed cocoons in the 

 bottoms of the cells of the host nests (ordinarily Vespula spp.). These 

 hatch in mid-spring or early summer into the "overwintering form," 

 which consists of both sexes. (There is one record of such cocoons 

 hatching in their third year.) In reared material males of the over- 

 mntering form are about one third as common as females. Collected 

 males are very scarce. The overwintering form disappears in the 

 field in early summer, by which time the females have presumably 

 located new small nests of Vespula and parasitized some of the cells. 

 By late July parasitized cells occur in moderate numbers in a portion 

 of Vespula nests. Parasitized cells increase until the end of summer. 

 The parasite larvae are found in the pupal cells of the wasp. Mor- 

 ley states (1900, Ent. Monthly Mag., vol. 36, p. 120) that they occm- 

 first on the growing larvae, but this seems improbable. There are 

 one to about seven parasite larvae per host. They feed on the ab- 

 domen of the pupa and when mature spin cocoons in the bottom of 

 the cell. The bottommost cocoons are tough, ribbed, and yellow or 

 light brown. These overwinter and hatch the following spring as 

 males and females of the "overwintering form." Many such cocoons 

 brought into the laboratory have hatched in the fall, but this may not 

 be common in nature. Above the bottommost angular, tough cocoons 

 are usually some flimsy whitish cocoons, spun apparently by larvae 

 of the same batch. These hatch in a few days as the "summer form," 

 consisting only of females and often brachypterous. The summer 

 form females usually stay in the nest and parasitize more cells. Fully 

 winged specimens of this form are not rare in the open, however, so 

 some of them must fly about and infest new nests. 



The two forms may be distinguished in the adult as follows : 

 Overwintering form: Males and females; clypeus about 2.8 as 

 wide as it is long on the midline, its apical 0.45 i inflexed; white or 

 pale yellow markings on head and pronotum rather extensive, the 



