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Drosophila pararubida Mather is a large light brown fly* with three pale off white longitudinal stripes on the thorax. This is one of the commonest species found in large numbers on fermenting fruit and garbage, and can be easily collected over banana baits in the tropical rain forests of Papua and New Guinea. It was first collected by Mather in 1959 who trapped it along with other species of Drosophila while collecting from that territory and later described as a new species related to immigrans species group (Mather, 1961). Angus (1961) and Mather (1961) have given collection records of this species from widely separated regions of Papua and New Guinea. Mather (unpublished) also collected it from Kuching in 1963. To date this species has only been recorded from Kuching Malaysia, and from the territory of Papua and New Guinea. It has not been recorded from any parts of Australia, although the closely related species, D. immigrans, D. setifemur and D. rubida are found in Queensland. It appears that D. pararubida like D. setifemur. However, unlike D. rubida it would seem to be quite successful in town, breeding on over-ripe fruit and garbage. Near Rabaul this was the dominant species over citrus fruit and cocoa pods, (Mather, 1961). D. pararubida can be very easily maintained in culture and breeds well on corn-meal medium. The life cycle which takes approximately 22 days from egg to egg at 25°C is almost twice as long as that of D. melanogaster (Demerec, 1950). The eggs lie buried deeply in the food medium, have four tapering filaments projecting above the surface. They take approximately 20 hours to hatch at 25°C. The adult males and females take an unusually long time to mature after eclosion. Whereas the males of D. immigrans mature six hours after eclosion (Spencer, 1940), the males of D. pararubida take up to 72 hours. In culture, females are not stimulated until they are at least four days old, and these when inseminated delay oviposition for 2-3 days. Females which are kept separate may not lay eggs for eight days if they are not inseminated. For recovering virgin females it is safe to keep freshly emerged males and females together for a period of three days. The flies remain in copulation from one minute to forty-five minutes, nine minutes being the average time. The giant chromosomes from third instar larval salivary glands squashes are extremely good. Because this species occurs extensively in the Australian region, is very easy to culture, and has excellent salivary glands, it is worth investigating genetically. In the present work visible mutants detected both after X-ray irradiation and in natural populations have been investigated. The cytology of the mutant forms has also been investigated. Most mutants studied are available in culture. *similar in size to D. immigrans |
