Larval feeding preference and performance of the cotton bollworm, Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), on different flower parts of cosmos

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Larvae of the polyphagous moth, Helicoverpa armigera (Lepidoptera: Noctuidae), were observed feeding intensively on disc florets of Cosmos bipinnatus Cav. (Asteraceae) in fields in western Japan during autumn. We compared larval feeding preference and performance, such as the survival rate, developmental period and pupal weight between disc florets and ray florets of C. bipinnatus in the laboratory. Larvae showed a strong preference for disc florets of C. bipinnatus. Larvae reared on disc florets showed a higher survival rate, and developed more quickly into heavier pupae than larvae reared on ray florets, suggesting that either disc florets provide the required nutrients or that ray florets contain secondary metabolites that negatively affect larval development. Although the mechanisms that elicit larval preference to disc florets remain unknown, our study demonstrated that disc florets alone generated improved growth of H. armigera larvae and might be an important food source in late autumn when larvae are preparing for overwintering.