1985] 
Bowers — Euphydryas 
45 
the hybrids were intermediate in their hostplant choice (Table 1). In 
general, pre-diapause larvae will attempt to feed on any plant that 
contains iridoid glycosides (Bowers, unpublished), although there 
may be differences in larval growth, survival, and digestive effi- 
ciency on hosts and non-hosts (Rausher, et al., 1982; Bowers, in 
prep.). Despite this general attraction of iridoid glycosides, purebred 
larvae in this experiment clearly chose the hostplant normally used 
in their population of origin. One interesting exception occurred in 
the offspring of the female from Satus Pass. One group of larvae ate 
only P. breviflorus, while all the others overwhelmingly preferred S. 
albus (Fig. 1). Post-diapause larvae at Satus Pass are found feeding 
on a Penstemon species, and this may be a factor in this result. 
The feeding preference of the hybrid larvae overall was inter- 
mediate between that of the two parental species. Each group of ten 
larvae appeared to choose one of the leaf discs, but some groups 
chose S. albus and others chose P. breviflorus. Individual larvae 
were not tested, but hybrid individuals may prefer one or the other 
plant species, however, there appeared to be no division of the 
groups of larvae such that some individuals were feeding on one disc 
and some on the other — the larvae fed together on the same disc. As 
with many gregarious insect species, survival of individual Euphy- 
dryas larvae may be lower than that of groups, thus social facilita- 
tion or group effect is likely to be important in the feeding patterns 
actually observed. In these hybrid larvae, the genotype that is in the 
majority may guide the feeding of the rest of the group. Alterna- 
tively, all the larvae may be intermediate between the parental pref- 
erences and thus a choice is a function of factors other than 
genotype, such as position of the larvae. 
The offspring of individual females all behaved similarly (Table 
1): all purebred E. chalcedona larvae preferred P. breviflorus, and 
although the offspring of only one E. colon female were tested, these 
larvae overwhelmingly preferred S. albus. Among the hybrid larvae, 
some groups preferred one plant species and others the other, while 
some showed no significant preference (Table 1, Fig. 1). There were 
no significant differences among the four females in the behavior of 
their offspring. Thus behavior of hybrid larvae did not differ from 
one female to the next. Although the offspring of only one E. colon 
female were tested, these larvae overwhelmingly preferred S. albus 
(Table 1). There was no significant effect of the female on the host- 
