Several eusocial wasps are prominent invaders to remote islands. The paper wasp Polistes chinensis antennalis is native to East Asia, was introduced to New Zealand in 1979 and has expanded its distribution there. This provides an excellent opportunity to examine the impacts of an initial bottleneck and subsequent expansion on genetic structure. We analysed and compared the genetic population structures of the native (Japan and South Korea) and invasive New Zealand populations. Although 94% of individuals had shared haplotypes detected across both populations, the remaining 6% had private haplotypes identified in only one of the three countries. The genetic variation at microsatellite loci was lower in New Zealand than in native countries, and the genetic structure in New Zealand was clearly distinct from that in its native range. Higher frequencies of diploid-male- and triploid-female-producing colonies were detected in New Zealand than in the native countries, showing the reduction in genetic variation via a genetic bottleneck. At least two independent introductions were suggested, and the putative source regions for New Zealand were assigned as Kanto (central island) and Kyushu (south island) in Japan. Serial founder events following the initial introduction were also indicated. The estimated dispersal distance between mother and daughter in New Zealand was twice that in Japan. Thus, the introduction history of P. chinensis antennalis in New Zealand is probably the result of at least two independent introductions, passing through a bottleneck during introduction, followed by population expansion from the point of introduction.

The rice stem borer, Chilo suppressalis (Walker) is an important lepidopteran pest of rice plants in Japan, and feeds on both rice (Oryza sativa) and water-oats (Zizania latifolia). We evaluated the difference in mating time of the two feeders under both laboratory and field conditions. The male moth of the water-oat feeders (WF) began to mate 7 h after the beginning of the scotophase, about 4 h later than the peak of mating of the rice feeders (RF). In accordance with this result, the body size of males trapped using synthetic sex pheromones differed between the two trap periods (sunset to 1:00 am vs. 1:00 am to sunrise) in the field, suggesting that the rice feeders were trapped earlier than the water-oat feeders. However, there was no unequivocal evidence showing limited gene flow between the two feeders at the level of allozyme polymorphisms. These results suggest that as the two feeders of C. suppressalis have recently diverged, the allozyme loci have not yet diverged to fixation.

Four microsatellite loci were isolated and characterized from the rice stem borer moth Chilo suppressalis, which is an important insect pest of rice plants in Japan. These loci were not in linkage disequilibrium; however, in two of four loci, the observed heterozygosities were significantly less than expected, possibly due to the effect of null alleles. Although caution should be taken in analysis, these loci were sufficiently polymorphic to be used for population genetic analysis of this species.

A polymorphic microsatellite locus was isolated and characterized from Polybia paulista , one of the most common polygynic, swarm-founding social wasps in Brazil. Three other microsatellite loci for which the primer sets were originally developed in independent-founding paper wasps also showed polymorphism in the size of amplification products in P. paulista .

BackgroundIn animals, the offspring sex ratio is modulated by kin conflict and cooperation, and determining the ratio is a main concern in evolutionary biology. Male competition for access to local mates is predictive of a female-biased sex ratio in the offspring (local mate competition; LMC). Conversely, female competition for access to local resources is predictive of a male-biased sex ratio in the offspring (local resource competition; LRC). However, several factors other than competition should synergistically operate in real-world populations. In the Australian paper wasp Ropalidia plebeiana, LRC and local resource enhancement (LRE) may operate simultaneously. To determine whether this is the case, we evaluated colony sex ratios and examined whether competition and/or enhancement operates at the population level in this species. ResultsIn spring, many foundress queens started their colonies by comb-cutting, in which nest combs from the previous season were divided into several combs to be reused. Genetic relatedness among foundresses did not differ before and after comb-cutting. Relatedness among foundresses was 0.339, whereas relatedness among new foundresses was 0.589, revealing nearly functional monogyny. The global FST value calculated with mtDNA markers was higher than that calculated with microsatellite markers, even after we corrected for differences in effective population sizes between sexes. This finding indicates female philopatry, which was also confirmed by mark–release–recapture before and after the hibernation of new foundresses. The colony sex ratio of reproductives became slightly biased toward males in larger colonies. In addition, both the number of foundresses and number of workers were positively associated with the number of reproductives, which indicates that LRE was also operating.ConclusionsOur results suggest that although the population structure seems to meet the requirements of LRC, the sex ratio is not modulated solely by LRC. Instead, the availability of female helpers at the founding stage likely mitigates the sex ratio predicted by LRC through LRE. Thus, LRC at the founding stage and LRE at the reproductive stage synergistically modulate the colony sex ratio in R. plebeiana.