Comparative Studies of Reproductive Diapause in North American Populations of ThreeHippodamiaSpecies (Coleoptera: Coccinellidae)

Quantifying responses of three congeneric species of lady beetles, Hippodamia parenthesis (Say), Hippodamia convergens (Guerin), and Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), to abiotic factors that influence their seasonal biology provides an understanding of the phenology of these species in North America. The developmental response and the induction and duration of adult hibernal diapause in four North American populations of H. parenthesis, collected between 40° N and 44° N latitude, was determined when beetles were reared at four photoperiods (L:D 16:8, 14:10, 12;12, and 10:14) at 22°C. Preimaginal development of the four H. parenthesis populations reared at the photoperiods was affected by population, photoperiod, and the interaction between population and photoperiod. Fifteen to 19% of H. parenthesis females reared at L:D 16:8 entered diapause, whereas shorter photoperiods (L:D 12:12 and 10:14) induced diapause in all females. Variation in response to L:D 14:10 was observed among the four populations of H. parenthesis, similar to the response observed in H. convergens and H. variegata. In contrast to the response of H. parenthesis females, in which four individuals oviposited at L:D 12:12 or 10:14 within 120 d, the duration of reproductive diapause in H. convergens and H. variegata females at L:D 12:12 and 10:14 showed a prolonged quantitative response to photoperiod. Comparisons of the responses (days to first oviposition) to photoperiod of H. parenthesis and H. variegata from the same collection sites showed significant differences at most photoperiods. Similarly, responses at all photoperiods varied between H. parenthesis and H. convergens from similar latitudes in Iowa.