Genetic relationships among certain species of the Aedes (Stegomyia) scutellaris group (Diptera: Culicidae).

Genetic affinities between species of the Aedes (Stegomyia) scutellaris group were determined through experimental hybridization. In this investigation Aedes hebrideus and Ae. scutellaris katherinensis were reciprocally crossed with Ae. polynesiensis, Ae. pseudoscutellaris, Ae. kesseli, Ae. malayensis, Ae. alcasidi and Ae. afbopictzu. Data on insemination and egg hatch rates w-ere recorded in the reciprocal crosses. Of these, Ae. hebrideus and Ae alcasidi, Ae. hebrideus and Ae. s. katherinensis, Ae. malayensis and Ae. hebrideus, and Ae. malayensis and Ae. s. katherinensis, were unidirectionally compatible using female parent of former species of the two. The reciprocal crosses of these laid infertile eggs. Aedes s. katherinensis and Ae. alcasidi were bidirectionally compatible. All other interspecific crosses were incompatible producing infertile eggs. In the compatible-crosses, i.e. where the viable hybrids were obtained, F, and hybrid fertilities were determined. Species hybrids obtained by crossing Ae. malayensis females and Ae. s. katherinensis males yielded lower fertility in F, and differential fertility when backcrossed. Species hybrids obtained by crossing Ae. s. katherinensis females and Ae. afcasidi males resulted in lower fertility in F, and also when backcrossed to Ae. s. katherinensis females. All other species hybrids were fertile. Based on the data obtained, Ae. hebrideus, Ae. s. kathminensis, Ae. malayensis and Ae. alcaridi formed a sub-grouping which showed remote genetic affinities individually or as a group with rest of the species investigated. Of several Aedine species groups, Aedes (Stegomyia) scutellaris is the most interesting from genetics and evolutionary standpoints due to its number of species, distribution pattern and medical importance. It consists of over 30 closely related species distributed in the Southeast Asia, South Pacific and Northern Australia (Marks, 1954; Belkin, 1962; Huang, 1972; Huang and Hitchcock, 1980). Many of its species are endemic to single islands isolated by natural geographical barriers in the South Pacific. Some species are vectors of bancroftian filariasis, e.g. Ae. polynesiensis, while others are susceptible to infection by related filarial worms (Macdonald, 1976; Trpis et al., 1981) . Most of these species can be easily colonized in the laboratory and cross-mated without any forced copulatory assistance. To establish the genetics of this species group, there has been considerable interest in experimental hybridization among its various species (see Macdonald, 1976; Rai et al., 1982). Such studies were further extended by Dev and Rai (1982), who provided information on crossing relationships on further species with additional data on those which had been crossed before. The present report is in continuation and includes observations on mating compatibility of Ae. hebrideus and Ae. scutellaris katherinensis with Ae. polynesiensis, Ae. pseudoscutellaris, Ae. kesseli, Ae. malayensis, Ae. alcasidi and Ae. albopictus. The data were recorded on insemination and egg hatch rates in the sex-ratios in various in terspecific crosses.