Offspring chemical control of adult reproductive transitions in a social insect

Parental care enhances offspring survival and growth but often entails a trade-off in which caregivers temporarily suppress their own reproduction to invest in existing young. Such reproductive transitions have independently evolved across diverse taxa, underscoring the advantage of prioritising current over future reproduction. In vertebrates, the behavioural sequence separating reproduction from parental care is controlled by offspring-derived cues. While many insects display obligate parental care, the role of brood cues in regulating adult reproduction remains unresolved outside advanced eusocial taxa, where reproductive plasticity has largely been lost. Here, we investigate reversible reproductive transitions in the clonal raider ant Ooceraea biroi, in which totipotent adults synchronously alternate between brood care and egg laying under larval regulation. Using custom behavioural assays, we show that larvae inhibit adult reproduction without physical contact, implicating volatile cues. Chemical analyses identified a previously undescribed larval-specific compound, methyl 3-ethyl-2-hydroxy-4-methylpentanoate (MEHMP), which is absent from other brood stages and ant species. Production of the compound closely tracked larval development and colony cycles, linking its abundance to reproductive synchrony. Exposure to synthetic MEHMP recapitulated the inhibitory effect of larval volatiles, confirming its role as a pheromone that suppresses adult egg laying. To our knowledge, this is the first identified brood pheromone that regulates reversible reproductive transitions in insects, and the first brood pheromone described in ants. By providing a direct chemical link between offspring presence and parental reproductive suppression, our findings highlight a convergent strategy across distant evolutionary lineages.