042. THE EFFECT OF THE INSECTICIDE PYRIPROXYFEN ON OVARY SYNTHESIS IN THE CHRISTMAS ISLAND RED CRAB, GECARCOIDEA NATALIS; A POSSIBLE CASE OF ENDOCRINE DISRUPTION?

Abstract

The yellow crazy ant, Anopholepis gracilipes is an invasive species on Christmas Island, Indian Ocean whose population needs to be controlled before there is irrevocable environmental damage. The insecticide, pyriproxyfen, a compound which mimics juvenile hormone of insects, has been proposed to do this. Before it can be used in the field, its effects on non target species such as the endemic red crab, Gecarcoidea natalis, need to be investigated. Land crabs, like all decapods, may utilise a similar hormone called methyl farnesoate which is thought to be involved in controlling early ovary development. Pyriproxyfen may also mimic methyl farnesoate and thus disrupt this process. The effect of pyriproxyfen on early ovary synthesis in G. natalis was investigated by feeding crabs a mixture of leaf litter and bait containing 0.5% pyriproxyfen (experimental groups) or a mixture of leaf litter and bait containing no pyriproxyfen (control groups) at simulated baiting doses (2 kg ha^–1 and 4 kg ha^–1). Two additional groups of crabs were fed ad libitum, either bait containing 0.5% pyriproxyfen or the control bait. Experiments were conducted from July to September of 2007. Red crabs synthesise their ovaries annually over two months (July to September) in the dry season. This situation of high nitrogen demand is funded from small excesses of nitrogen assimilated from a mainly leaf litter diet. Pyriproxyfen affected early ovary development. Ovaries from crabs in the experimental groups at all baiting levels had a higher total nitrogen content and dry mass than that of the control animals. The ovaries from the experimental animals were also more mature; they contained more previtellogenic and early vitellogenic oocytes, of a larger diameter, than ovaries of the control animals. Significant amounts of pyriproxyfen were accumulated in the target tissues, the midgut gland and ovary. Minor amounts of pyriproxyfen were accumulated in muscle, a non-target tissue. By mimicking methyl farnesoate, pyriproxyfen may have caused endocrine disruption in G. natalis. In particular it may have stimulated early ovary development and synthesis of yolk protein.