Starving honey bee (Apis mellifera) larvae signal pheromonally to worker bees.
Communication between parents and young offspring for food provisioning presents an area of potential conflict between the amount of food requested by young and the optimal resource allocation by the parents. This has become an area of increasing interest to evolutionary biologists1. Recent studies mainly focused on parent-offspring conflicts in mammals and avian species2,3,4. In these species since parents are equally related to their offspring they are expected to favour an even division of food to their young1, however, varying condition of young offspring will also influence allocation decisions. In many species parental provision is in relation to begging intensity as a proxy of offspring need and condition rather than the real food needs of hungry sibs1. For example, pigeons (Columba livia) and sows (Sus scrofa) allocated more food to loudspeakers playing begging calls rather than the hungry young5,6. On the other hand, young offspring often try to acquire a disproportionately larger investment from their parents than their sibs by making louder begging calls and attempt to manipulate their parent to obtain more food than the parents’ optimal resource allocation3,4. Nevertheless the costs of begging calls curtail call exaggeration and help to ensure their honesty7. Furthermore, environmental factors also influence the degree of parent-offspring conflict: for instance, a shortage of food could reduce the honesty of begging signals and increase sibling scramble competition4; Adding unrelated broodmates increases barn swallow chicks’ begging intensity8. These influential studies of parent-offspring conflict in mammals and birds illustrate the potential complexity of communication over resource allocation. As an advanced eusocial insect, honey bees have a radically different social organisation for brood rearing. The single queen in the colony lays all the eggs but young larvae are reared by their adult sisters rather than their parents9. During the larval stage, each larva is fed 1.5 ± 0.2 times/h by nurse bees not randomly10,11, and thousands of larvae need to be fed daily9. Brood rearing is the primary function of a honey bee colony, but the potential for conflict between brood and nurses over resource allocation in this specialized society has thus far not been explored because it has not been clear whether the largely immobile larvae are capable of begging for food. Generally, begging signals in vertebrates are body movements and acoustic signals12,13,14,15. Pervious studies showed that some insect larvae such as wasp larvae (Vespa orientalis F) and beetle larvae (Nicrophorus vesoilloides) produce acoustic or tactile signals to beg for food16,17. It is well documented that larval honey bees produce pheromones capable of altering adult worker behaviour18,19,20. Therefore, it is possible that honey bees could use volatile pheromones as their begging signal to attract workers to them when hungry. This has been demonstrated for bumble bees, although the exact composition of the pheromone remains unknown21, and the possibility has been suggested for honey bees22. Here we explored whether honey bee larvae signal their hunger pheromonally. Our findings suggest that a volatile component of brood pheromone, E-β-ocimene, is a candidate begging signal for young honey bee larvae. It is actively synthesized by hungry larvae and attracts workers to inspect cells.