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Summary Direct observations have suggested that the closely related wood ants Formica polyctena and F. rufa represent different social organizations, with high queen number in F. polyctena and a high frequency of monogynous nests in F. rufa. We examined social organization and genetic population structure in a setup where populations of the two species are sympatric and gene flow between the species is possible. Our aim was to compare social organization in the species, and study evolutionary relationships between them. The observed relatedness among colony workers suggested that the difference in the level of polygyny is quantitative rather than qualitative, with a higher queen number in F. polyctena. The observed difference in polygyny was not accompanied by a difference in spatial genetic differentiation which was weak in both species. The genetic distance between the species is consistent with limited interspecific gene flow. Identification of a few possible F. rufa migrants in F. polyctena populations suggests potential interspecific gene flow. Thus, reproductive isolation of the species may not be complete when they are sympatric.

Thirteen polymorphic microsatellite loci were developed for blowflies for use in studies of genetic differentiation in wild populations of Lucilia illustris, to detect the possible occurrence of bottlenecks and to study changes in genetic variation in laboratory populations of Lucilia sericata following artificial bottlenecks. In this preliminary study it was revealed that heterozygosity was lower than expected in wild populations and genetic variation had been lost in the laboratory population despite being kept at a large size.

The mechanism of sex determination assumed widespread in parthenogenetically arrhenotokous Hymenoptera is that of single locus complementary sex determination (CSD). Functionally sterile diploid males are produced under CSD and generate a genetic load, the cost of which increases with inbreeding. We quantify diploid male production (DMP, proportion of diploid individuals that are male) using a morphological criterion (adult fresh weight) and genetical (microsatellite DNA) markers in a communal, sexually size-dimorphic bee, Andrena scotica, which inbreeds. Male genotypes suggested a DMP of 0.003. The inbreeding coefficient, f, was significantly positive (+0.165), equivalent to 44% of matings being among full sibs (predicted DMP of 0.11). We hypothesize three non-mutually exclusive explanations to account for the large difference between the low observed (in males) and high expected (derived from ffor females) DMP: (i) multilocus CSD, (ii) «sex allele signalling» tied to mate selection, and (iii) sperm selection within mated females. The costs of inbreeding through DMP are apparently low in A. scotica.

The mechanism of sex determination assumed widespread in parthenogenetically arrhen‐otokous Hymenoptera is that of single locus complementary sex determination (CSD). Functionally sterile diploid males are produced under CSD and generate a genetic load, the cost of which increases with inbreeding. We quantify diploid male production (DMP, proportion of diploid individuals that are male) using a morphological criterion (adult fresh weight) and genetical (microsatellite DNA) markers in a communal, sexually size‐dimorphic bee, Andrma scotica, which inbreeds. Male genotypes suggested a DMP of 0.003. The inbreeding coefficient, f, was significandy positive (+ 0.165), equivalent to 44% of matings being among full sibs (predicted DMP of 0.11). We hypothesize three non‐mutually exclusive explanations to account for the large difference between the low observed (in males) and high expected (derived fromy ffor females) DMP: (i) multilocus CSD, (ii) ‘sex allele signalling’ tied to mate selection, and (iii) sperm selection within mated females. The costs of inbreeding through DMP are apparendy low in A. scotica.

During their introduction, non-native species typically undergo founder events that reduce genetic variation. To allow a high-resolution genetic investigation of introduced populations of the small Indian mongoose (Herpestes javanicus), we developed primers for nine variable microsatellite loci. Their applicability was assessed in 10 mongooses from the large Fijian population, which originated from a single pair from Calcutta, India. The number of alleles ranged from two to five per locus, possibly as a result of preservation of initial variability and in situ mutations during the rapid population expansion after introduction.