Effects of Temperature and Photoperiod on the Immature Development in Cassida rubiginosa Müll. and C. stigmatica Sffr. (Coleoptera: Chrysomelidae)

Abstract

Tortoise beetles (Cassida and related genera) are a large cosmopolitan group that includes several pests of agricultural crops and natural enemies of weeds but their biology and ecology remain poorly known. Using a set of environmental chambers, we address simultaneous efects of temperature and photoperiod on immature development and adult body mass in two European species, C. rubiginosa and C. stigmatica. Consistent with its broader distribution range, the former species is less susceptible to low rearing temperatures, develops faster and has a larger body mass than the latter. However, C. rubiginosa seems to be less adapted to late-season conditions as a short-day photoperiod accelerates its immature development to a lesser extent than it does in C. stigmatica, which nevertheless results in greater larval mortality and slightly but signifcantly smaller adults. By contrast, in C. stigmatica, which is more likely to encounter late-season conditions due to its slower life cycle, short-day acceleration of development is achieved at no cost to survivorship and fnal body mass. The experiment with C. stigmatica was repeated during two consecutive years with diferent methods and the main results proved to be well reproducible. In addition, laboratory results for C. rubiginosa agree with feld data from literature.