Reproductive plasticity ofVespula pensylvanica(Hymenoptera: Vespidae) on Maui and Hawaii Islands, U.S.A.

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Abstract
Reproductive activities of Vespula pensylvanica (Saussure) were studied on the recently invaded (1978) islands of Maui and Hawaii. Aspects of reproductive behaviour were inferred from the use of attractant traps to monitor foraging worker and queen populations, observations of architecture and traffic rates of nests, and dissections of queens occupying active nests or captured while foraging. Most wasp colonies adhered to the basic annual cycle dominant throughout V. pensylvanica's native temperate range. Atypical overwintering colonies, indicated by at least one episode of large cell construction and a subsequent reversion to small cell construction, occurred on both islands, but were detected in only some years. Overwintered colonies had peak traffic rates in excess of 300 worker sorties per minute, but some large annual colonies also had traffic rates greater than 300 per minute. Flying queens were most abundant during the spring (March-June), but were captured in every month except January. Among autumn queens taken from nests on Hawaii, oviposition-ready queens were more common than hibernation-ready queens, suggesting that winter hibernation is not obligatory. Polygyny, achieved by adding queens to an established colony, is a likely prerequisite for successful colony overwintering. Two gyne-addition mechanisms are proposed for this: retention of daughter queens, and joining by outside queens. Expression of V. pensylvanica reproductive plasticity is correlated with relaxation of climate- related constraints. Relaxation of genetic constraints is also hypothesised to contribute to the emergence of polygyny in Hawaiian Island populations.