Cytology and Sex Ratios of an African Species of Armored Scale Insect (Coccoidea-Diaspididae)

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Abstract
In the central highlands of Kenya, Aspidiotus simulans replaces the closely allied, cosmopolitan A. destructor which it also closely resembles cytologically. Both species have the commonest diaspidid chromosome numbers of 4 in the male and 8 in the female but in A. simulans the process of chromosome elimination, by which male haploidy is achieved in the armored scales, is atypical. Since sex is predetermined by whether or not elimination occurs, it is not surprising that unusual sex ratios would be found in a species with an unusual elimination process. In one collection, all gravid females contained either only male or only female embryos and the great majority of mothers were male producers. In other collections, such unisexual reproduction was rare or lacking but the bias in favor of males continued in evidence except in one small sample. Field observations have also been made of colonies with superabundant males. The suggestion is offered that flexible mechanisms of predetermination provide a means by which the sex ratio of a species may vary widely without production of inviable or infertile individuals.