Data from: Elucidating mechanisms for insect body size: partial support for the oxygen-dependent induction of moulting hypothesis

Body size is a key life history trait and knowledge of its mechanistic basis is crucial in life history biology. Such knowledge is accumulating in holometabolous insects, whose growth is characterised and body size affected by moulting. According to the oxygen-dependent induction of moulting (ODIM) hypothesis, moult is induced at a critical mass where oxygen demand of growing tissues overrides the supply that principally grows only at moults. Support for the ODIM hypothesis is controversial partly because of a lack of proper data to explicitly test the hypothesis. The ODIM hypothesis predicts that the critical mass is positively correlated with oxygen partial pressure (pO2) and negatively with temperature. To resolve the controversy that surrounds the ODIM hypothesis, we rigorously test these predictions by exposing penultimate-instar Orthosia gothica (Lepidoptera: Noctuidae) larvae to temperature and moderate pO2 manipulations in a factorial experiment. The relative mass increment in the focal instar increased along with increasing pO2, as predicted, but there was only weak suggestive evidence of the temperature effect. Probably due to a high measurement error in the trait, pO2 effect on the critical mass was sex-specific; high pO2 had a positive effect only in females, whereas low pO2 had a negative effect only in males. Critical mass was independent of temperature. Support for the ODIM hypothesis is partial because of only suggestive evidence of a temperature effect on moulting, but the role of oxygen in moult induction seems unambiguous. The ODIM mechanism, thus, seems worth considering in body size analyses.