E-B-ocimene and brood cannibalism: Interplay between a honey bee larval pheromone and brood regulation in summer dearth colonies

Authors: Carroll, Mark; Brown, Nicholas; HUANG, E. - Former ARS Employee

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/2/2025
Publication Date: 2/6/2025
Citation: Carroll, M.J., Brown, N.J., Huang, E. 2025. E-B-ocimene and brood cannibalism: Interplay between a honey bee larval pheromone and brood regulation in summer dearth colonies. PLOS ONE. 20(2). Article e0317668. https://doi.org/10.1371/journal.pone.0317668.
DOI: https://doi.org/10.1371/journal.pone.0317668

Interpretive Summary: Honey bees often rear fewer brood during nutritionally-stressed dearth periods when forage is scarce. Worker bees restrict the colony bee populations during forage shortages primarily through brood cannibalism of eggs and young larvae. Colonies that engage in brood restriction during long periods of nutritional stress can fail to rear sufficient replacement brood. We examined the effects of brood cannibalism in nutritionally-stressed colonies on a key pheromone produced mainly by eggs and younger larvae. E-ß-ocimene is a volatile pheromone that accelerates worker maturation from nursing to foraging and promotes brood care in older larvae. Egg and young larvae consumption by brood cannibalism removes the main ocimene producers from the colony. We examined how ocimene production changes in nutritionally-stressed dearth colonies presented with pollen, a known stimulant of brood rearing. Dearth colonies immediately resumed brood rearing and curtailed brood cannibalism when fed supplemental pollen. This resumption of egg and young larvae rearing was accompanied by sharp increases in ocimene volatile levels. Adult workers that developed in pollen-supplemented dearth colonies had better nutrient stores and jelly-producing glands (hypopharyngeal glands) than workers from unsupplemented colonies. Given the increase in ocimene emissions once brood rearing resumed, we considered the possibility that ocimene suppresses brood cannibalism and initiates egg rearing in stressed colonies. We tested whether synthetic ocimene odors emitted in the brood nest (simulating healthy eggs and young larvae) could prime brood rearing in nutritionally-stressed colonies. We treated broodless nucleus colonies with a synthetic vial release of ocimene equivalent to 300 eggs/young larvae. All nucs supplemented with ocimene had large numbers of eggs and young larvae four days after treatment initiation. None of the supplemented nuc colonies engaged in complete consumption of eggs and young larvae. By contrast, half of the unsupplemented nucs cannibalized all of their eggs and young larvae. Most of the remaining unsupplemented nucs retained considerably fewer eggs and young larvae after four days. Similar releases of ocimene from eggs and young larvae may reduce brood cannibalism in nutritionally stressed colonies. Beekeepers may be able to use supplemental E-ß-ocimene to stimulate brood rearing in colonies emerging from dearth (poor forage) conditions.

Technical Abstract: Honey bees often reduce brood rearing during nutritionally-stressed dearth periods when forage is scarce. Worker bees restrict the colony bee population during food scarcity primarily through brood cannibalism of eggs and young larvae. Colonies that engage in brood restriction during long periods of nutritional stress can fail to rear sufficient replacement brood. We examined the effects of brood cannibalism in nutritionally-stressed colonies on a key pheromone produced mainly by eggs and younger larvae. E-ß-ocimene is a volatile pheromone that accelerates worker maturation from nursing to foraging and promotes brood care in older larvae. Population regulation by brood cannibalism removes the main ocimene producers from the colony. We examined how ocimene production changed in nutritionally-stressed dearth colonies presented with pollen, a known stimulant of brood rearing. Dearth colonies immediately resumed brood rearing and curtailed brood cannibalism when fed supplemental pollen. This resumption of egg and young larvae rearing was accompanied by sharp increases in ocimene volatile levels. Adult workers that developed in pollen-supplemented dearth colonies had better nutrient stores and jelly-producing glands (hypopharyngeal glands) than workers from unsupplemented colonies. Given the increase in ocimene emissions once brood rearing resumed, we considered the possibility that ocimene helps suppress brood cannibalism and initiate egg rearing in stressed colonies. We tested whether synthetic ocimene odors emitted in the brood nest (simulating healthy eggs and young larvae) could prime brood rearing in nutritionally-stressed colonies. We treated broodless nucleus colonies with a synthetic vial release of ocimene equivalent to 300 eggs/young larvae. All nucs supplemented with ocimene had large numbers of eggs and young larvae four days after treatment initiation. None of the supplemented nuc colonies engaged in complete consumption of eggs and young larvae. By contrast, half of the unsupplemented nucs cannibalized all of their eggs and young larvae. Most of the remaining unsupplemented nucs retained considerably fewer eggs and young larvae after four days. Similar releases of ocimene from eggs and young larvae may reduce brood cannibalism in nutritionally stressed colonies. Beekeepers may be able to use supplemental E-ß-ocimene to stimulate brood rearing in colonies emerging from dearth (poor forage) conditions.