Studies on the inheritance of susceptibility to infection withBrugia pahangiandWuchereria bancroftiin theAedes scutellarisgroup of mosquitoes

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Abstract
Three western species of the Aedes scutellaris group, A. alcasidi, A. hebrideus and A. scutellaris katherinensis, were tested for susceptibility to infection with Brugia pahangi and sub-periodic Wuchereria bancrofti. All were fully refractory to infection. Female A. alcasidi and A. s. katherinensis were crossed with males of A. polynesiensis and/or A. cooki, both of which are susceptible to B. pahangi and are natural vectors of W. bancrofti. The female hybrids were backcrossed to the parental susceptible stocks. The hybrids and the back-cross progeny were tested for filarial susceptibility. A. cooki was homozygous for the sex-linked marker white-eye. The hybrids were mostly refractory to infection; 4·9% were susceptible to B. pahangi and 1·7% susceptible to W. bancrofti. The susceptible hybrids carried a much lower worm load than the A. polynesiensis controls. The progeny of the backcross (A. s. katherinensis X A. polynesiensis) X A. polynesiensis had susceptibility rates of 14·8 and 25·7% to B. pahangi and W. bancrofti respectively. The pooled data, which were homogeneous, gave a rate of 23·1%. The progeny of the backcross (A. alcasidi X A. cooki) X A. cooki included both white- and black- eyed females. If susceptibility were sex-linked, the white-eyed progeny would be susceptible, except for the cross-over class, and the black-eyed progeny refractory. Only one of six white- eyed mosquitoes was susceptible to B. pahangi: in a large sample of black-eyed offspring 18·8% were susceptible to B. pahangi or W. bancrofti. The data suggest that nuclear factors are involved in the inheritance of susceptibility to the filarial infections, but there is no evidence of a single major gene. The observed susceptibility rates among the hybrids and backcross progeny do not permit a conclusion on the mode of inheritance of susceptibility factors, but the agreement between the results with B. pahangi and W. bancrofti supports the use of the former parasite as a laboratory model for studies of vector genetics.