Portrait of an Ephemeral Adult Stage: Egg Maturation, Oviposition, and Longevity of the Gall Midge <I>Rhopalomyia californica</I> (Diptera: Cecidomyiidae)

Abstract

Insect reproduction is typically spread out in time and space, making estimates of lifetime reproductive success quite difficult under natural field conditions. Such estimates are, however, critical to providing rigorous tests of theory for reproductive behavior. One approach to circumventing this problem is to study insects whose lifetime reproduction is compressed in space and time, and whose ovarian dynamics (oogenesis, oosorption, and oviposition) are simplified. We investigated the gall midge Rhopalomyia californica Felt (Diptera: Cecidomyiidae) as a possible candidate for an herbivore with such a simplified pattern of lifetime reproduction. We demonstrate here that R. californica matures all of its eggs before adult eclosion (it is strictly proovigenic), and it does not resorb eggs, even when deprived of oviposition sites. Observational and experimental studies in the field demonstrate that this midge typically completes its entire lifetime reproduction in a single day: females usually emerge at dawn, mate, and after a posteclosion period of resting, they initiate a sustained period of active oviposition during which most eggs are laid over a 4–5-h period. Mean longevity of adult females is very short, consistently <1 d and only 5–6 h on clear and warm days. Two key aspects of senescence are experimentally demonstrated: an increase in mortality rates and a decrease in oviposition rates with age. The life history traits associated with the ephemeral adult stage of R. californica are consistent with a syndrome that has been characterized recently for many proovigenic herbivorous and parasitic insects. Proovigenic species, including R. californica, may be particularly valuable as model systems for studies of lifetime reproductive success in nature.