Resource use by an introduced and native carrion flies.

The carrion fly Chrysomya rufifacies has recently been introduced to North America. Larvae of this species are facultative predators on other carrion larvae, and are known to reduce populations of the New World fly Cochliomyia macellaria in the laboratory and in certain field situations. In order to identify conditions under which native taxa might avoid interaction with the invader, we examined broad patterns of resource use by capturing postfeeding larvae as they left a carcass. The Calliphorinae were least similar to C. rufifacies since they were able to exploit smaller carrion, showed a peak in density during cold weather while C. rufifacies numbers were low, and occurred much earlier than the invader during succession within a carcass. Phormia regina also was most abundant during cold weather. The Sarcophagidae were able to exploit smaller carcasses than the invader but are likely to encounter it in larger carcasses. C. macellaria was the species most similar to C. rufifacies in carrion use, and probably is reduced in number by the invader wherever they coexist. In contrast to all other taxa, C. rufifacies exited a carcass alone, suggesting that other larvae of the same age were attacked. Manipulation of a conspicuous predator, the ant Solenopsis invicta, revealed a negative effect on numbers of P. regina and C. macellaria.