Influence of temperature and light on the development of moth larvae: Different response in the sister species Orthosia gothica and Orthosia cerasi

Abstract Climate change influences the average global temperature and seasonality of our planet, therefore affecting animals' phenology. Insects have been found to show longer development times and increased growth rates at higher temperatures, with their developmental stages also being influenced by light availability. To disentangle the effects of temperature and light on their development and growth, we reared larvae of the two moth species Orthosia gothica (Linnaeus, 1758) and Orthosia cerasi (Fabricius, 1775) under four conditions, consisting of two ambient temperatures, namely 15 and 20°C, and two different light cycles, namely 24 h of darkness and 12 h of light followed by 12 h of darkness. During the growth of the larvae, their biomass and size were measured repeatedly, and the pupation date of the larvae was recorded. We predicted that both higher temperature and light availability would have a positive effect on both the larvae's growth and development time. Our experiment showed that larvae of both species developed significantly faster at 20°C. However, light availability had opposing effects on larval growth: it promoted final biomass and pupation date in O. gothica , but had negative effects on O. cerasi . These results support the idea that increasing temperatures will generally promote larval development and growth in moths. However, our findings also show that even closely related species can exhibit contrasting responses to light availability, suggesting that the influence of photoperiod on larval development is species‐specific and may be linked to ecological or behavioural traits.