1979] 
Dunkle — Xertos pallidus 
335 
before the wasp emerges from the pupa. Brues (1905) compared a nest 
of annularis taken in July with one collected in October in Texas. In 
the adult October wasps he found X. pallidus larvae as well as adults. 
Thus possibly in the present study non-extruded Xenos may have 
been missed. However, I dissected 49 male P. annularis whose abdo¬ 
mens looked abnormal, but no X. pallidus were found. Brues sug¬ 
gested that all the wasps carrying male Xenos die before the next 
spring since he saw none with male pupal cases in the spring. This 
would also mean the death of the female pallidus in the same wasp 
carrying males. If this is so, the effect on the populations of both host 
and parasite could be severe. 
Pierce (1909) reported on two large colonies of Texan annularis 
taken in September and kept alive through October containing 1311 
male and 242 female wasps. The males were 19.8% parasitized by 
pallidus, the females 2.9% parasitized. One male wasp carried 15 male 
pallidus, whereas the highest parasite load in the present study was 8 
males with 2 females. Pierce states that several queen wasps with 
empty male pallidus puparia were found hibernating, but whether 
such queens could reproduce the next spring remains unproved. 
Pierce (1909) also states that male pallidus did not protrude from the 
host until several days after the host left its pupal cell, a contradiction 
with Hubbard (1892). The winged males left the host 10-17 days after 
the host became adult. 
Pierce (1918) points out that in Delphax (Homoptera) the female 
strepsipteran is located more anteriorly in the host than the male 
probably because the female is smaller than the male, the reverse of 
the case in pallidus. Salt (1927) found no morphological change at all 
in a small series of annularis carrying pallidus, nor was any change 
except deformation of the abdomen noted in the present study. 
According to Bohart (1941) only two strepsipterans are known to 
parasitize Polistes in North America, pallidus in annularis and X. 
peckii Kirby in several other species. The most extensive study of X. 
peckii was done by Schrader (1924). She found extreme differences in 
infestation rates, from 0 to 25%, in different localities in New Eng¬ 
land. The parasites extruded from the host after the wasps emerged 
from pupae, the males 5-10 days before the females. The sex ratio of 
larval X. peckii was 38 male: 37 female. Further work on both species 
of Xenos in North America, and comparison between them, is certain 
to provide much new information on the evolution of parasite/host 
interactions in a very interesting system. 
