How is a queen replaced within the hive?
Of the three contexts in which colonies rear queens, swarming is by far the best understood. During spring development, rapid growth of adult and brood populations congests the nest, reducing or interrupting circulation of queen mandibular pheromone (QMP). Some areas therefore lack the signal inhibiting new queen rearing. Several queen cells develop, typically along comb edges where pheromone distribution is limited, even while the mother queen remains present. Beyond the collective decision to swarm, associated with insufficient queen signalling in an overcrowded nest, studies have clarified when and how swarms depart. There is no empirical evidence that workers choose to leave or remain according to their relatedness to the replacement queen. Age may instead be important: younger workers tend to leave, plausibly improving swarm survival. The vibrational signals workers use to announce departure are well described. After the primary swarm separates, with approximately 75% of workers gathering on nearby vegetation as a temporary cluster, the search for a new home begins. A small number of scouts search for, locate, assess and advertise sites, demonstrating collective decision-making and swarm intelligence. Individual scouts do not compare several sites; they use dances to advertise their assessment of the visited cavity’s structural integrity, volume and other objective features. Given alternatives, swarms almost always choose the most favourable available nest.
A second context is emergency queen rearing, when a queen suddenly dies or is physically removed. The immediate absence of QMP prompts workers within hours to rear queens from worker larvae, commonly in central areas of the comb. It remains unclear which larvae are selected, but the process is far from random. Some colony subfamilies are much more represented among queens than among workers, and egg size probably matters, though much remains unresolved. Queens mate with many males—polyandry—so their daughter queens can belong to different subfamilies with the same mother but different fathers. This creates potential conflict over the eventual queen. Much research has therefore investigated whether this conflict produces actual nepotism during queen rearing. Less attention has focused on elimination of surplus virgin queens, which restores a colony to monogyny, or one queen. A recent study by Long et al. found workers’ vibration signals strongly associated with queens that survive, even though virgins ultimately kill one another rather than being killed by workers.
The third context is supersedure, driven by a relatively poorly understood set of factors: workers replace their queen without an emergency or the need to swarm. In the past, research focused on reproductive potential, assuming poor queens were invariably replaced. The picture appears more complex. Queens are not replaced only when reproductive potential is low; replacement also appears more frequent after exposure to pesticides or infection by parasites. Further complicating matters, pathogen-exposed queens can produce offspring with greater resistance, termed transgenerational immune priming.
Supersedure is probably triggered by reduced perception of combined fertility signals from the queen’s pheromones and the brood. We remain far from fully understanding the process. Here, the author proposes a conceptual model centred on workers’ theoretical assessment of the queen’s genetic potential at any given time. At every stage of colony life, workers face a binary choice: retain or replace her according to these factors. This leads to a threshold model: above it, workers collectively keep the queen; below it, they replace her. Assuming workers initially rate her overall potential highly, her finite lifespan means this perception eventually crosses the threshold, initiating supersedure.
Studies suggest supersedure may occur prematurely, bearing in mind that queen replacement changes the genetic composition of subsequent offspring. Likely influences on workers’ assessment include reproductive potential, pheromonal signals, brood—especially larvae—as a fertility signal, worker demographics and genetic composition, internal conditions such as nutrition and genetic diversity, and external conditions such as pesticide exposure and abiotic stress. Understanding how these factors interact across the queen’s life offers an important direction for research into collective reproductive decisions.
In this model, the author argues that supersedure is driven not simply by intrinsically poor queen quality, but by workers’ perception of her reproductive potential. Their assessment is subjective and context-dependent rather than an absolute instrumental measurement of reproductive potential, fecundity or fertility. If supported, this would mean supersedure reflects social and abiotic conditions within the colony, rather than merely an accurate signal of a queen’s reproductive capacity.
Questions worth investigating include:
Can infection in workers alter their individual foraging decisions and thus collective colony decisions? If so, could it similarly affect the decision to initiate supersedure?
Studies show pesticides can alter bee behaviour and perception. Exposure could therefore affect workers’ pheromone reception and initiate premature replacement. Could colony demography, within its genetic and social structure, also influence collective queen-replacement decisions?
David R. Tarpy
Adapted from:
Collective decision-making during reproduction in social insects: a conceptual model for queen supersedure in honey bees (Apis mellifera) — David R. Tarpy Open access, Current Opinion in Insect Science
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