CHAMPAIGN, Ill. — Honey bee larvae lack the sophisticated olfactory capabilities of adult honey bees, a new study finds. Scientists point to this temporary loss-of-function as a side effect of the nurse bees’ heroic level of brood care, calling it a consequence of social evolution.
The new findings are detailed in the Proceedings of the National Academy of Sciences .
Honey bees are highly eusocial, an evolutionarily advanced system in which reproduction is limited to one or a very few individuals while nonreproductive workers care for the young. Various bee species differ in the amount of attention they bestow on their young, with honey bees representing one of the most intensive levels of care.
In their short lives, most honey bees go from being helpless larvae — confined to honeycomb cells made of wax and dependent on a horde of nurse bees for their roughly 100 daily feedings and inspections — to adults that take on the various duties required to maintain and protect the colony, said Gene Robinson , an entomologist and the executive director and CEO of the Discovery Partners Institute at the University of Illinois Urbana-Champaign. Robinson led the new study with U. of I. postdoctoral researcher Tianfei Peng .
Because they are so well cared for, honey bee larvae have no need to feed themselves, unlike the larvae of many other insect species. Nurse bees regularly deposit small droplets of food — honey, pollen and royal jelly — directly in the larval cells, and the larvae slowly twirl around in their chambers until they encounter the food.
Adult honey bee foragers must be able to distinguish odors from a vast number of potential sources of pollen and nectar. For this, they rely on a suite of chemosensory receptors, including olfactory receptors, or ORs, and ionotropic receptors, or IRs. The new study focused on a coreceptor, ORCO, that is essential to OR function; and IR25a, one of several coreceptors needed for proper IR function.
The researchers wanted to know if expression of these genes differed between the larval and adult bees and, if so, whether the larvae had an impaired ability to sniff out food in their environment.
In a series of experiments, the team found that gene expression of ORCO in the antennae and brain was reduced in honey bee larvae compared with their adult counterparts. And when removed from their cells and presented with drops of food nearby, the larvae demonstrated no ability to detect the food or move toward it. In other experiments, the larvae also failed to move away from a drop of acetic acid, a known repellent, or to show preference for a pheromone associated with queen bees. Adult bees would quickly detect and respond to such cues.
“In contrast, several IR genes showed relatively higher expression in larvae than other chemosensory receptors,” the researchers wrote. This included IR25a, which plays a role in the larval sense of taste.
“Larval honey bees might be able to only taste, but not smell, their food,” Robinson said.
Previous studies in other animals have found that evolution sometimes deletes unneeded attributes completely, with associated losses in the genome.
“For example, some species that live in dark environments, such as cave-dwelling fish, have permanently lost the neural and molecular machinery needed to process visual information, a phenomenon known as regressive evolution,” the researchers wrote.
“But what we documented in honey bees is a temporary loss, for only one part of the life cycle and not the whole life cycle,” Robinson said. “They can’t lose the gene, because the adult bee needs to be able to detect these odors, so instead they regulate expression of the gene.”
“We discovered this developmentally regulated loss-of-function is a result of low gene expression, not gene loss,” Peng said.
The Illinois Sociogenomics Initiative and the National Institutes of Health (R35GM147420) supported this research.
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Editor’s notes :
To reach Gene Robinson, email generobi@illinois.edu .
To reach Tianfei Peng, email ptianfei@illinois.edu .
The paper “Social evolution and diminished olfactory function in larval honey bees” is available online.
DOI: 10.1073/pnas.2615678123
Proceedings of the National Academy of Sciences
Observational study
Animals
Social evolution and diminished olfactory function in larval honey bees
14-Jul-2026
The authors declare no competing interest.