Ecological studies of the breeding sites and reproductive strategies of domestic species of Drosophila

The ecology and reproductive strategies of seven species of domestic Drosophila were examined at a wholesale fruit and vegetable market. The seasonal abundance of adult Drosophila was investigated using baited traps. The value of different trapping methods was discussed. Drosophila were reared from different fruits and vegetables brought back from the market to the laboratory. D. melanogaster, D. simulans and D. subobscura nearly always emerged from fermenting fruits, D. busckii specialised on decaying vegetables, and D. immigrans and D. hydei were generalists. Within the groups, fermenting fruit and decaying vegetables there was considerable overlap of breeding sites. Some of the factors which might influence breeding site preferences were investigated in the field and in the laboratory. Both selection of breeding sites by ovipositing females and differential survival of the larvae seem to be important. Unlike other species of Drosophila the domestic species do not seem to separate their feeding and breeding sites. D. immigrans, which frequently breeds in citrus fruits, was found to be particularly associated with these fruits when they were infected with the mould, Penicillium. Other species emerged more often from uninfected fruit. There may be a long standing evolutionary relationship between D. immigrans, citrus fruits and Penicillium. The body size of D. melanogaster, caught in traps, was found to change in a regular way during the season. This was partly an effect of temperature, but partly due to intraspecific competition at the highest population densities. Intraspecific competition is unimportant in the other species, though some species suffered from interspecific competition with D. melanogaster. The reproductive strategies of the seven Drosophila species were examined. They fell into two groups, large species with large clutches of small eggs, and small species with small clutches of large eggs. These strategies are not consistent with r— and K— selection theory, but may have been linked to the predictability of finding breeding sites. The ecology of domestic species of Drosophila was discussed with reference to current theories of population regulation.