Effect of Air Humidity on Sex Ratio and Development of Ladybird Harmonia axyridis (Coleoptera: Coccinellidae)

Abstract

Length of development of larvae and pupae of the invasive alien ladybird beetle Harmonia axyridis, their survival rates, sex ratio, and fresh mass of the emerged adults were measured at three contrasting levels of relative air humidity: 30, 60, and 90%, 25°C and photoperiod 16L : 8D. Overall sex ratio was 51%, but there was a strong trend for higher proportion of males at low humidity and higher proportion of females at high humidity. Survival rate, larval developmental time, and adult mass were all differently influenced by air humidity depending on the food type. In individuals fed with aphid Acyrthosiphon pisum there was a trend for better survival, shorter development, and higher mass gained at higher humidity. These trends were opposite or nonsignificant in individuals fed with frozen eggs of moth Ephestia kuehniella.