How do worker policing and reproductive conflict stabilize cooperation in highly related insect societies?

Why does policing keep the peace in a colony of relatives?

In a colony of closely related insects, workers share many genes, so helping the queen's offspring can be a good evolutionary strategy. But workers are not identical, and each worker can sometimes gain more by laying its own male eggs than by helping raise the queen's sons. This creates a reproductive conflict: individual selfishness can undermine the cooperative enterprise. Worker policing—where workers (and sometimes the queen) eat eggs laid by other workers—directly suppresses this selfish behavior [1].

The direct effect is straightforward: in the bumblebee Bombus terrestris, worker-laid male eggs are nearly all eaten soon after being laid, by the queen and by other workers, while queen-laid eggs survive. This explains why very few worker-produced males ever reach adulthood, even though worker-laid eggs are just as viable as queen-laid eggs [1]. By removing the payoff of selfish egg-laying, policing keeps reproduction concentrated in the queen and preserves the cooperative division of labor.

Policing works even better when workers stop trying

Policing does more than punish selfishness after the fact. When a policing system is in place, individual workers have less incentive to attempt reproduction at all, because their eggs are likely to be destroyed. This voluntary restraint in response to policing is called "acquiescence," and models of inclusive fitness confirm that workers should be less tempted to act selfishly when policing is effective [2].

Acquiescence helps explain a striking pattern: in many insect societies, very few workers ever attempt to reproduce, and immature females usually develop as workers rather than queens. The mere existence of a credible policing system shifts the cost-benefit calculation for each individual, so cooperation becomes the best option even for a selfish actor [2]. In this way, policing stabilizes cooperation not only by coercion but by removing the temptation to defect.

High relatedness is not the whole story

It is tempting to assume that worker policing exists because workers are more closely related to the queen's sons than to other workers' sons—a relatedness difference that would favor policing. But the bumblebee B. terrestris is monandrous (queens mate with a single male), so workers are highly related to each other and such relatedness differences are weak. Yet classical worker policing still occurs: worker-laid eggs are eaten, queen-laid eggs are spared, and workers discriminate between them using cues on eggs and egg cells that almost certainly come from the queen [1].

This suggests that worker policing can originate through reproductive competition among workers themselves—as "selfish" policing—even without the relatedness differences that were thought to maintain it in honeybees. In other words, high relatedness may make cooperation possible, but policing can arise from conflict among workers and then help hold the society together [1].

Other ways insect societies manage reproductive conflict

Policing is not the only mechanism at work. In some cooperatively breeding paper wasps, dominance hierarchies determine who reproduces, and when a breeder is lost, a previously non-reproductive helper may inherit the reproductive role. In species like Polistes canadensis and Polistes lanio, succession can involve costly aggression, but non-competitive helpers appear to compensate by maintaining nest-level foraging efforts, which helps stabilize the colony through the disruption [3].

In other ants, queen dominance and worker policing together control reproduction, reinforcing the view that multiple layers of enforcement can keep reproductive conflict in check [5]. Across insect societies, the general picture is that cooperation is stabilized by a mix of relatedness, active policing, voluntary restraint, and sometimes dominance or succession rules—each reducing the incentive or opportunity for individuals to pursue their own reproduction at the colony's expense [2][3][5].

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