DIPLOID MALES IN A PRIMITIVELY EUSOCIAL BEE, LASIOGLOSSUM (DIALICTUS) ZEPHYRUM (HYMENOPTERA: HALICTIDAE).

Hymenoptera are characterized by a haplo-diploid mechanism of sex determination. Females are diploid and males are haploid. However, in many species diploid males may occur if individuals are homozygous at a sex determining locus. Diploid males were found in three out of four populations (nest aggregations) of the primitively eusocial, halictine bee Lasioglossum zephyrum for which samples of males were examined electrophoretically. The frequency of diploid males was greater in a small, geographically isolated population (the "Robinson" nest aggregation) than in a large population that had nearby neighboring populations (the "Salmon Creek A" nest aggregation). In addition, the proportion of polymorphic loci was lower in the Robinson nest aggregation suggesting that a bottleneck event or loss of alleles due to small population size occurred in the Robinson population that involved a loss in the number of alleles at the sex determining locus.