Genetic variability in a thelytokous form of Aphytis mytilaspidis (Le Baron) (Hymenoptera: Aphelinidae)

Abstract

The possible mechanisms for generation of genetic variability in a thelytokous form of the parasitic Aphelinid Aphytis mytilaspidis (Le B.) were investigated. Through cytological studies the thelytokous form was found to retain the meiotic divisions in egg maturation. Restoration of diploidy is achieved through the fusion of two sister nuclei of the second meiotic division (terminal fusion). Heterozygosity can be retained for such loci as undergo crossing-over. Males are produced by the thelytokous form in a low frequency; both thelytokous males and females are sexually functional, and sexual processes occur in the thelytokous population. In zones of overlap, gene flow may occur between the thelytokous form and a related arrhenotokous form, thus adding to the genetic variability of the thelytokous form. Since genetic variability can be generated in the thelytokous form through genetic recombinations in meiosis, through sexual processes within the population, and by introgression with the arrhenotokous form, thelytoky does not represent an evolutionary dead end.