Like all terrestrial organisms, insect eggs face a tradeoff between exchanging metabolic gases (O2 and CO2) and conserving water. Here I summarize the physiology underlying this tradeoff and the ecological contexts in which it may be important. The ideas are illustrated primarily by work from my laboratory on eggs of the sphingid moth Manduca sexta. In particular, I discuss: (1) dynamic changes in metabolic demand and water loss during development; and (2) how the eggshell layers and embryonic tracheal system control the traffic of gases between the embryo and its environment. Subsequently, I identify three areas with interesting but unresolved issues: (1) what eggs actually experience in their microclimates, focusing particularly on the leaf microclimates relevant to eggs of M. sexta; (2) how egg experience influences whether or not hatchling larvae succeed in establishing feeding sites on host plants; and (3) whether Hetz and Bradley's [Hetz, S.K., Bradley, T.J., 2005. Insects breathe discontinuously to avoid oxygen toxicity. Nature 433, 516-519] oxygen toxicity hypothesis for discontinuous gas-exchange cycles applies to insect eggs. © 2009 Elsevier Ltd. All rights reserved.

Neonate Water loss Egg Desiccation Oxygen

terrestrial ecosystem gas exchange host plant Manduca sexta desiccation Sphingidae embryonic development Manduca oocyte moth trade-off physiology oxygen consumption metabolism energy metabolism Hexapoda oxygen Larva Time Factors Animals water microclimate animal ovum Article egg Lepidoptera Carbon dioxide neonate time