PERFORMANCE OF TRIRHABDA VIRGATA (COLEOPTERA: CHRYSOMELIDAE) ON THREE POTENTIAL HOSTS

The suitability of three potential host plants, Solidago canadensis L. var. canadensis (Asteraceae), Solidago graminifolia (L.) Salisb., and Aster lateriflorus L. (Asteraceae), for the goldenrod beetle, Trirhabda virgata LeConte was determined by measuring several fitness components during the T. virgata life cycle. Neonate larvae were collected from S. canadensis plants and transplanted onto S. canadensis, S. graminifolia, and A. lateriflorus and maintained in field enclosures until the last instar was reached. Once brought into the laboratory, larvae were fed their assigned host plant until pupation. Following emergence, adults were weighed and separated into mating pairs to record oviposition and longevity. Eggs were kept in the laboratory until the following spring, when first instar larvae were taken into the field and re-established on their assigned host, and the experiment was repeated for 2 years. Larval survival and rate of development was not affected by the host plant. Mean weight of adults at emergence was greater on S. canadensis than on either S. graminifolia or A. lateriflorus. Two components of adult fitness, postmating longevity and realized fecundity, were measured. Longevity of adult female T. virgata was not affected by the host plant. Fecundity of T. virgata reared on A. lateriflorus and S. graminifolia was lower than the fecundity of females reared on S. canadensis. These results are consistent with the hypothesis that both intrinsic plant quality and the mobility of the foraging stage are important in the evolution of host range in T. virgata. These experiments were repeated over a 3-year period, using offspring from the survivors of the previous year for the 2nd and 3rd years. Over this time, individuals experienced "laboratory adaptation," and both accepted and increased their performance on previously unacceptable food plants.