SUPPRESSION OF DROSOPHILA ANANASSAE FLIES OWING TO INTERSPECIFIC COMPETITION WITH D. MELANOGASTER UNDER ARTIFICIAL CONDITIONS

摘要

Interspecific competition between two species of Drosophila: D. ananassae and D. me-lanogaster was studied at the larval and adult stages. It was found that when D. ananassae and D. melanogaster adult flies were co-cultured, very few D. ananassae offspring could be recovered in the first generation. To investigate the reasons of D. ananassae apparent inhibition, mating behavior of D. ananassae in the presence of D. melanogaster was observed and it was found that the number of matings deviated significantly from those recorded when it was kept alone. To determine larval development of D. ananassae after being initially exposed to D. melanogaster, the females of the two species were separated in different food bottles after 3 days of being kept together. Good D. ananassae cultures could be recovered indicating that initial exposure of D. ananassae to D. melanogaster did not hamper its egg laying capacity or eclosión. However, if they remained together, no D. ananassae could be recovered from larvaldiet, suggesting that either D. melanogaster adults interfered with fertilization or egg-laying, or their larvae eliminated competitors. To see whether there is larval competition, polytene chromosomes of 54 third instar larvae were analyzed out of whichonly 5.56 percent were found to be D. ananassae. Thus, if a few eggs are laid by D. ananassae and they develop, all the while facing competition from D. melanogaster and till the third instar larval stage is reached, there is almost complete eliminationof D. ananassae. Thus, interspecific competition exists at all stages of life cycle and few if any D. ananassae flies emerge.