Intraspecific nest usurpation by foundresses was studied in 2 haplometrotic (solitary founding) species of different subgenera, Polistes (P.) riparit's and P. (Polistella) snelleni, in areas where they cohabited. The overall probability for a nest to be usurped by a foreign foundress during the season was about twice as large in P. snelleni as in P. riparius. In both, however, probability of usurpation was largest on late pre-emergence nests, or in late June and early July. In P. riparius, all the usurpers of known origins were those foundresses that had lost their pre-emergence nests to destruction probably by some vertebrates; in P. snelleni, some usurpers had the same history as above, while the
Production characteristics, including colony productivity, labor efficiency and sex ratio, in the paper wasp Polistes snelleni were compared between cool-temperate (Hokkaido, northern Japan) and warm-temperate (Nagano and Kanto, central Japan) populations, based on examination of old nests. The production schedule of P. snelleni was protandrous. Numbers of workers, males and gynes produced per colony were all larger in the warm-temperate populations. The numbers of reproductives (males plus gynes) per worker were generally greater in cool-temperate than in warm-temperate colonies, although some extraordinarily large warm-temperate nests had very high gynes/worker ratios. The number of males was not significantly correlated with the number of workers in either cool-temperate or warm-temperate populations. Differences in the production characteristics between populations are discussed in terms of climatic conditions, a major factor in differences in the length of the nesting period. The production of reproductives in very large warm-temperate nests is discussed in relation to worker reproduction.
Parasitic nematodes of the genus Sphaerularia are known to infect and sterilize the overwintering gynes (potential queens) of bumblebees. We found that 70% of the overwintered gynes of the hornet Vespa simillima collected using bait traps were infected and sterilized by Sphaerularia sp. This is the first solid record of parasitism by Sphaerularia in hornets (Vespa spp.).
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