Incidence of Apocephalus horridus in colonies of Camponotus vicinus and the effect of antibiotic/antimycotic mixtures on fly emergence (Diptera: Phoridae; Hymenoptera: Formicidae)

The incidence of the ant-decapitating fly (Apocephalus horridus (Borgmeier), Diptera:Phoridae) in colonies of the carpenter ant Camponotus vicinus (Mayr)(Hymenoptera:Formicidae) was investigated in western Oregon. Flies were present in 3 of 8 colonies sampled at levels ranging from 1 to 15% of the workers sampled. Flies tended to be more prevalent in medium sized workers, suggesting that larger, major workers were not preferred by ovipositing flies. Feeding studies indicated that the addition of a mixture of propiconazole and tetracycline to a glucose diet increased ant decapitation, suggesting the fly larvae were given some advantage by the treatments. Exposure of workers to elevated temperature (39degreesC) for 48 hours decreased the incidence of decapitation suggesting that heat affected the development of fly larvae in the parasitized ants. Exposure to high temperature for short periods may rid the ants of the parasites and could be a reason for the occurrence of satellite colonies in warmer and drier locations than the parent colony in C. vicinus. The results suggest that the incidence of A. horridus in carpenter ant colonies might be manipulated by feeding workers compounds that encourage successful parasite development.