Do hornets have zombie workers?

Area of Science:

• Evolutionary biology
• Social insect behavior
• Chemical ecology

Background:

• Colonies of the European hornet (Vespa crabro) are typically founded by a single queen.
• Kinship patterns predict worker-queen conflict over male production in social insects.
• Previous studies on related vespine wasps suggest workers may reproduce.

Purpose of the Study:

• To investigate the predicted worker-queen conflict over male production in Vespa crabro.
• To determine the reproductive roles of queens and workers in European hornet colonies.
• To explore the mechanisms underlying reproductive control in Vespa crabro.

Main Methods:

• DNA microsatellite analysis of 282 male hornets.
• Ovary dissections of 500 workers from eight nests.
• Direct behavioral observations of four nests for 50 hours.

Main Results:

• European hornet males are exclusively produced by queens.
• Workers rarely have activated ovaries and do not attempt to lay eggs.
• No direct aggression between queens and workers was observed, contrasting with predictions.

Conclusions:

• Worker self-restraint or queen control, possibly pheromonal, explains the absence of worker reproduction.
• The findings challenge existing models of reproductive conflict in vespine wasps.
• The study also identified diploid males and double matrilines, indicating unusual reproductive events.