Reduced efficiency of tropical flies (Diptera) in the decomposition of snail cadavers following molluscicide poisoning

Decomposition is a key ecosystem service that reduces non-living organic matter, returning nutrients to the soil. In this study, we examine the responses by fly (Diptera) communities to molluscicide-poisoned apple snail (Pomacea canaliculata) cadavers in a tropical rice production landscape. Fewer molluscicide-poisoned cadavers were colonised by decomposer flies (niclosamide = 61% of cadavers with fly larvae; methaldehyde = 53%; Camellia sp. seed extract [saponin] = 50%) compared to control (freezer-killed) cadavers (81%). Metaldehyde, niclosamide and saponin reduced the abundance (average 51% reduction), biomass-density (average 63% reduction) and species richness (average 38% reduction) of flies emerging from the snail cadavers. The decay of control cadavers was generally faster (57% more tissue removed over 3 days) than molluscicide-treated cadavers. We suggest that poisoned carcasses potentially affect ecological communities across a range of trophic levels.