RESOURCE USE BY AN INTRODUCED AND NATIVE CARRION FLIES

The carrion fly Chrysomya rufifacies has recently been introduced to N orth America. Larvae of this species are facultative predators on othe r carrion larvae, and are known to reduce populations of the New World fly Cochliomyia macellaria in the laboratory and in certain field sit uations. In order to identify conditions under which native taxa might avoid interaction with the invader, we examined broad patterns of res ource 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 weat her while C. rufifacies numbers were low, and occurred much earlier th an 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 encounte r it in larger carcasses. C. macellaria was the species most similar t o C. rufifacies in carrion use, and probably is reduced in number by t he invader wherever they coexist. In contrast to all other taxa, C. ru fifacies exited a carcass alone, suggesting that other larvae of the s ame age were attacked. Manipulation of a conspicuous predator, the ant Solenopsis invicta, revealed a negative effect on numbers of P. regin a and C. macellaria.