Photoperiodic effect on size-related metamorphosis in the milkweed leaf beetle, Labidomera clivicollis

ABSTRACT. Photoperiod significantly affected size-related aspects of metamorphosis in the milkweed leaf beetle Labidomera clivicollis (Kirby) (Chrysomelidae). Larvae reared under short-day photoperiod successfully pupated at lower weights than larvae reared under long-day photoperiods. This short-day effect was observed to an equivalent extent in both males and females; but within photoperiod treatments, males consistently pupated at lower weights than females. It is likely that the short-day effect on metamorphosis is associated with photo-periodically induced changes in larval corpora allata activity or juvenile hormone titre. Ecologically, the short-day effect on metamorphosis may enhance the moulting success of larvae which encounter food shortages during autumn.