40 
Psyche 
[Vol. 92 
(1982, 1983) has shown that there is genetic variation in hostplant 
preference among individual females from a single population, as 
well as differences among females from different populations. Vari- 
ation in the ability of Euphydryas larvae to use different hostplants 
has been investigated by several workers (Rausher, et al., 1981; 
Holdren and Ehrlich, 1982; Williams, et al, 1983a, b; Bowers, in 
prep.); however the genetic basis of larval preference in this genus 
has not been addressed. 
The hostplants of the North American Euphydryas include pri- 
marily three families: Scrophulariaceae, Plantaginaceae, and Capri- 
foliaceae; with occasional use of plant species in the Oleaceae 
(Bowers, 1980); and Valerianaceae (Williams and Bowers, in prep.). 
These plants are all characterized by the presence of a group of 
secondary compounds, the iridoid glycosides (Kooiman, 1972; 
Jensen, et al., 1975; Bowers, 1981) which are used as larval feeding 
stimulants by E. chalcedona and probably by the other species as 
well (Bowers, 1983). 
Neonate larvae potentially provide a powerful tool with which to 
examine the genetic basis of hostplant selection because their host- 
plant choice behavior is not complicated by the phenomenon of 
conditioning (Jermy, et al., 1964). Conditioning causes larvae to 
exhibit a preference for the plant species on which they have been 
feeding, and in some cases this may occur over a short period of 
time (Hanson, 1983). Hostplant choice of first instar larvae is usu- 
ally considered to be constrained by the oviposition behavior of the 
female. However, Holdren and Ehrlich (1982) found that neonate 
larvae of E. editha and E. anicia may move as much as 15 cm in 
search of fresh food. Euphydryas hostplants include some species 
that are small annuals, and they may be defoliated or otherwise 
unsuitable as food, thus forcing even first instar larvae to move in 
search of other food. Ovipositing females may make mistakes 
(Chew, 1974), and although this may be rare in Euphydryas, in the 
laboratory, females with their feet on the hostplant, may lay their 
eggs on an inappropriate substrate (pers. obs.). The ability of newly 
hatched larvae to move in search of appropriate food is clearly 
important in the event of such a situation. 
With these considerations in mind, I undertook a study of two 
species of Euphydryas, E. colon and E. chalcedona. These two spe- 
cies are very closely related (Bauer, 1975) and in the past have been 
