EFFECTS OF ANT PREDATION AND LARVAL DENSITY ON MYCOPHAGOUS FLY COMMUNITIES

The effects of ant predation and larval density on mycophagous fly com munities were examined in two field experiments conducted in a mixed-o ak forest 10 km N of Greenville, SC, USA. In the first experiment, fir st instar Drosophila tripunctata larvae (brown-eyed mutants) were plac ed on Agaricus bisporus mushrooms at five densities (0, 10, 20, 40 and 80/mushroom). Mushrooms were placed in ''ant-access'' and ''ant-exclu sion'' treatment cups for six days, and native metamorphs that emerged were sorted, counted, dried, and weighed. Predation had a significant effect on the number of metamorphs emerging, reducing fly abundance f rom 57.2 flies in the ant exclusion cups to 37.5 in the ant access cup s. Larval density was also important; decreasing the number of metamor phs from 60.5 flies (10 larvae/mushroom) to 20.5 flies (80 larvae/mush room). In the second experiment, halves of native boletoid mushrooms w ere placed in the ant treatment cups for six days and metamorphs were sorted. Predation reduced the number of flies emerging by 60%. In both experiments, however, there were no significant effects on species ri chness or Berger-Parker dominance. Likewise, there were only slight co mpensatory increases in mean fly mass in the ant-access treatments. It appears that ants are removing post-interactive third instars and thu s do not decouple competitive interactions or alter community composit ion.