Worker Matricide in Social Bees and Wasps

In bumble bees (Bombus) and vespine wasps (Vespa, Vespula, Dolichovespula), workers have regularly been observed to kill their colonyʹs single queen (worker matricide). Workers gain a fitness payoff in worker-produced males from matricide because it removes the queenʹs inhibition over their reproduction. There is selection for the queenʹs death when this gain outweighs the fitness penalty of losing queen-derived offspring. A kin selection model explores this condition for three parties, the queen, nonlaying workers, and laying workers. Matricide is favoured by (i) annual life cycles, (ii) late-season colonies, (iii) declining queen productivity, (iv) male-only production by queens, and (v) single mating. Conflict and relative power among workers also affect whether matricide occurs. Existing data largely support these predictions. Queen dominance loss arguably culminates in matricide because of positive feedback between the queenʹs condition and worker treatment of her. Worker matricide represents an extreme form of kin-selected queen-worker conflict over sexual production.