Do hornets have zombie workers?

Colonies of the European hornet, Vespa crabro, are typically founded by a s ingle queen mated to a single male. From the resulting colony relatedness p attern we predicted strong worker-queen conflict over male production where both the workers and the queen attempt to produce the colony's males. To t est for this conflict, male production was studied in 15 hornet nests using a combination of DNA microsatellite analysis (282 males), worker ovary dis sections (500 workers from eight nests) and 50 h of observation (four nests ). In contrast to our prediction, the data show that hornet males are queen s' sons, that workers never attempt to lay eggs, rarely have activated ovar ies, and that there is no direct aggression between the queen and the worke rs. This contrasts with other data for vespine wasps, which support related ness predictions. Dolichovespula arenaria has the same kin structure as V. crabro and workers produce males in many colonies. The similarity between t hese two species makes it difficult to explain why workers do not reproduce in V. crabro. Self-restraint is expected if worker reproduction significan tly reduces colony productivity but there is no obvious reason why this sho uld be important to V. crabro but not to D. arenaria. Alternatively, queen control may be important. The absence of expressed queen-worker conflict ru les out physical control. Indirect pheromonal control is a possibility and is supported by the occurrence of royal courts and queen pheromone in Vespa but not Dolichovespula. Pheromonal queen control is considered evolutionar ily unstable, but could result from a queen-worker arms race over reproduct ive control in which the queen is ahead. The genetic data also revealed dip loid males in one colony, the first example in the vespine wasps, and two c olonies with double matrilines, suggesting that occasional usurpation by sp ring queens occurs.