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.

Cannibalism is a behavioral trait seen in a number of species and can be favored when the fitness gain outweighs the cost. In social wasps, field studies have suggested that food limitation causes larval cannibalism as a compensation of a meal for adult wasp and/or earlier production of the first workers, but experimental studies for the effect of food availability on larval cannibalism have been very scarce. Hence we examined whether Polistes chinensis antennalis foundresses exhibit a higher level of larval cannibalization under food-limited conditions than under food-available conditions. Larval cannibalization occurred frequently under both prey-and honey-limited conditions; however, young larvae were more frequently cannibalized than old larvae in the prey-limited colonies, while old larvae were more frequently cannibalized than young larvae in the honey-limited colonies. The number of days between colony initiation and the emergence of the first workers was not significantly different between the prey-limited and prey-available colonies, suggesting that under prey-limited conditions P. chinensis antennalis foundresses tend to cannibalize their young larvae and feed probably the flesh of these cannibalized larvae to old larvae in order to ensure the rapid production of the first workers. On the other hand, the number of days between colony initiation and the emergence of the first workers was longer in the honey-limited colonies than in the honey-available colonies. We propose explanations for the first time for why the foundresses in the honey-limited conditions cannibalized their old larvae more frequently than their young larvae in spite of this resulting in the delayed emergence of the first workers.

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In social insects, nestmate recognition systems can be dynamic and modulated in response to various kinds of genetic and environmental cues. For example, multiple-queen colonies can possess weak recognition abilities relative to single-queen colonies, due to broader exposure to heritable and environmentally derived nestmate recognition cues. We conducted field experiments to examine nestmate recognition ability in a neotropical polygynous wasp, Polybia paulista. Despite the fact that the effective queen number in P. paulista is the highest ever recorded in polygynous wasps, this species exhibits a well functioning nestmate recognition system, which allows colony entry only to nestmate individuals. Similar to other social Hymenoptera, young wasps express colony specific chemical signatures within several days after emergence. This is the first study to show that the polygynous epiponine wasp is able to distinguish nestmates from non-nestmates.

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