With spring in full bloom, bees are already busy doing their essential work as pollinators for crops and other plants.

For many, the image of bees buzzing among spring blossoms brings to mind bustling hives of female worker bees who do not reproduce, serving and protecting a queen bee who does.

How ovaries develop in female honeybees, sweat bees and others living in eusocial groups — complex social hierarchies where different “castes” perform different roles — has been well researched. Studies have been done on solitary bees who live alone and lay their eggs in nests in the ground.

But not as much is known about female bees who live in looser social hierarchies, such as the eastern carpenter bee (Xylocopa virginica), where females live together in small groups and can switch back and forth between dominant and subordinate roles.

Professor of Biological Sciences Miriam Richards is a member of the Brock Bee Lab and an expert on the eastern carpenter bee, which lives in Niagara and eastern U.S. Late last year, she and Biological Sciences Research Assistant James Mesich (MSc ’24) published a study examining ovarian development and survival in the species.

Juvenile hormone (JH) regulates a wide range of physiological and behavioural processes in female bees, including the shedding of their outer skeleton as they move out of the larval stage, dominant and subordinate roles they take on in adult life, their level of aggression and the development of ovaries.

Scientists use a human-made chemical substance called methoprene, a JH mimic also found in insecticides, to study how JH plays out in a variety of bee species. This enables researchers to study the impacts of JH on adult bee behaviour and physiology.

Richards says the role of juvenile hormone — as simulated through methoprene — in developing ovaries and regulating behaviours has never been investigated in “casteless” bee societies.

“We wanted to find out if we could manipulate female carpenter bees to become more dominant and to lay more eggs by treating them with methoprene,” says Richards. “First we had to find out if this would even work in casteless carpenter bees.”

Continuing a project that was part of his master’s research, Mesich applied a mixture of methoprene and acetone — a liquid that helps the methoprene to be absorbed into the bee’s body — to 34 adult female eastern carpenter bees collected in St. Catharines and Welland.

Some of the bees received the acetone alone. The mixtures contained several concentrations of methoprene.

The duo examined some of the bees’ ovarian development two and four days after exposure. They also monitored the health and longevity of other bees.

Their findings include that:

• Juvenile hormone, as simulated through methoprene, was shown to enhance ovarian development in adult female eastern carpenter bees, and that 500 micrograms of methoprene is the optimal amount to bring about this development.
• There was no differences in survival rates between bees that had been exposed to methoprene compared to those without exposure, rendering the methoprene safe to use in research.

“This was the first study of JH effects in social bees that don’t exhibit a caste system,” says Richards. “So, this is evidence that reproductive hormones affect casteless bees in ways similar to social bees that do exhibit castes.” 

She says the study results will guide researchers in future studies of ovarian development in female eastern carpenter bees.

The study also sets the stage for further exploration, says Mesich.

“Now that we know the proper dosage for affecting reproduction, we can expand our research to look for other effects of JH,” he says. “For example, could treating subordinate bees with methoprene make them more ‘dominant’ and if so what would that dominance look like in this species?”

Mesich and Richards’ study, “Effect of a juvenile hormone analogue (methoprene) on ovarian development and survival in the Eastern Carpenter Bee (Xylocopa virginica),” was published in the journal Insectes Sociaux in November.