Effects of photoperiod, temperature, and diet on the development of the banded woollybear, Pyrrharctia (Isia) isabella (J. E. Smith) (Lepidoptera: Arctiidae).

Abstract

The banded woollybear, Pyrrharctia isabella (J. E. Smith) was reared under laboratory conditions from egg to adult. Groups of individually reared larvae were kept at one of 8 photoperiods and in combination with one of 4 temperatures and were fed one of 6 artificial diets and fresh plantain. The times of moulting, head capsule widths, larval and pupal weights, and adult characteristics (fertility, sex) were recorded. Larvae were easily reared on bean, wheat germ, casein-wheat germ and fresh plantain, while casein, alfalfa, and plantain diets proved unsatisfactory. Development time increased at photoperiods longer than 14 hours. This increase was characterized by extra instars. The results suggest that scotophase may be more important than photophase in influencing development. Temperature did not affect overall larval development time although higher temperatures did slow the growth rate. Mature larvae were found to undergo an obligatory diapause in the Montreal-Ottawa area. Chilling was not an absolute requirement for diapause development, although mortality was high at higher temperatures. Diapausing larvae at 30°C were found not to be cold hardy. Increments in head capsule widths at each successive instar did not follow Dyar's rule. The relationships between voltinism and obligatory diapause, cold-hardiness and diapause, photoperiod, temperature and development, chilling and diapause development as well as Dyar's rule are discussed.