Oviposition site selection by the regal fritillary, Speyeria idalia, as affected by proximity of violet host plants

Selection of oviposition sites by female regal fritillary butterflies, Spey eria idalia (Drury), in relation to the location and abundance of their lar val food plant, Viola pedatifida G. Don, was studied in Kansas tallgrass pr airie. To identify potential cues that females use to select oviposition mi crosites, we compared plots in which eggs were laid with paired control plo ts in terms of violet abundance distance from plot center to the nearest vi olet plant, plant species composition and relative abundance, plant diversi ty (Shannon's index), and average plant canopy height. No significant diffe rences occurred between control and oviposition sites for any of these vari ables (P > 0.15). Violets were present in only 30% of the I-m-diameter ovip osition plots, compared with 24% of the corresponding controls. Furthermore eggs were never laid directly on violets even when they were present nearb y. These darn imply that S. idalia females do not preferentially orient to or oviposit on their larval food plant. Nevertheless, female S, idalia did not oviposit randomly, for they invariably chose microsites near the ground that were shaded by the grass/forb overstory and usually deposited eggs on the underside of dead vegetation. We speculate that environmental stresses such as high temperatures and intense solar insolation during the egg stag e or harsh overwintering conditions experienced by first-instar larvae impa ct survival and influence choice of oviposition sites. High fecundity (more than 2000 eggs in some individuals) may allow this species to use a condit ional, "sweepstakes" strategy, i.e., producing and spreading many eggs over prairie that harbors host plants to compensate for low egg and larval surv ivorship.