Annual and multi-year nests of the western yellowjacket, Vespula pensylvanica, in California

Summary.

This study compares life history data from northern and southern sites within the native range of Vespula pensylvanica: new data on nests and their contents from California and previously published data from Washington and Oregon. Annual nests in southern California have more combs and cells than Washington nests and continue to rear workers later into the season. Many nests in winter in California still contain workers, brood, and gynes, which has not been reported from other areas. Some V. pensylvanica nests become polygynous and persist for more than one season. This occurs mostly in California in its native range and in other warm-winter regions where it has been introduced. The polygynous California nests reported here are similar to previous reports from Hawaii. We discuss how overwintering differences in the warm-winter regions may contribute to polygyny.