Parthenogenesis in Coccids (Homoptera)

Abstract

SYNOPSIS. The cytology of 33 parthenogenetic coccids is reviewed and their parthenogenesis is classified into seven types: haploid and diploid arrhenotoky, facultative and obligate deuterotoky, facultative thelytoky, and obligate automictic and apomictic thelytoky. The origin of each type is briefly discussed. In three coccids with obligate automictic thelytoky, diploidy is restored by the fusion of haploid cleavage nuclei. Individuals of these coccids are thus expected to be completely homozygous for all loci. These coccids probably evolved from groups in which the males are either haploid or contain only one genetically active chromosome set. The evolution of thelytoky with complete homozygosity is attributed to the lesser significance of heterosis in male haploidy and related chromosome systems. Following a suggestion of Hughes-Schrader(1948), the high frequency of parthenogenesis in coccids is attributed to the fragility of the males.