Effects of larval density and food stress on life‐history traits of C naphalocrocis medinalis ( L epidoptera: P yralidae)

Abstract High population density and nutrition restriction can lead to phase variation in morphology and development, and subsequently induce changes in the reaction norms of adult flight in migrant insects. However, response of migratory propensity to such stress in Endopterygote insects, especially in several species of Lepidoptera, remains unclear. In this study, larval and adult developmental responses to crowding and food stress were investigated in the migratory moth, Cnaphalocrocis medinalis (Guenée). A high larval rearing density significantly reduced pupal mass, survival rate and female fecundity. Larvae developed rapidly under crowding conditions, and time to pupation was 2 days earlier than individuals reared alone. By contrast, short‐term starvation and associated compensatory growth prolonged larval duration by 3–4 days and pupal duration by 1–2 days. It also reduced the pupal mass, but showed no detectable effects on female reproductive performance. Both sexes had similar development strategies; however, females seemed to be more sensitive to crowding and food shortage than males. A positive effect was expected if such stress factors acted as cues that triggering a behavioural or physiological shift to a distinct migratory phase. To the contrary, we found no proof that crowding and starvation caused maturation delay in female reproductive development. All treatments did not significantly increase female pre‐oviposition period. Therefore, we concluded that life developmental responses to crowding and food shortage in this species were different. Adult migration propensity was not enhanced under such stress conditions during the larval phase.