Bees respond to the effects of wildfires by producing more female offspring

Corvallis, pray. Researchers at Oregon State University found that blue orchard bees, an important domestic pollinator, produce female offspring at higher rates in the aftermath of wildfires in bushfires.

The more intense the fire, the higher the percentage of females – more than 10% in the most severely burned areas compared to the less severely burned areas.

“This is one of the first studies to look at how the severity of wildfires affects the demographics of bees,” said Jim Rivers, an animal ecologist at the College of Forestry at Ohio State University. “The ratio differed between the sexes under different fire conditions, but the number of young children produced did not change, indicating that the bees changed the sex of their offspring depending on the degree of severity of the fire.”

Female bees control the sex of their offspring, laying fertilized eggs with sperm that become female, or unfertilized eggs that become male.

Bees pollinate the many flowering plants that make up local ecosystems and food chains. Understanding how fire – expected to increase in frequency and intensity – is an important part of knowing how post-fire management actions can help or harm bees.

“We placed the bees in various locations within a recently burnt mixed conifer forest in southwestern Oregon and used it as a measuring stick to tell us how well the bee environment was,” said Sarah Galbraith, a postdoctoral researcher at the College of Forestry. “Adjustment of offspring production toward the more expensive offspring sex shows a functional response to changes in habitat quality through increased density of flowering plants.”

Generally, pollinators benefit from canopy-limiting fires in dense coniferous forest ecosystems; Flowering plants usually increase in abundance for several years after a fire, resulting in food resources that enhance the diversity and abundance of wild bees.

Bees are the most important of Earth’s pollinators, which collect an estimated $ 100 billion in global economic impact each year. Oregon is home to more than 600 native bee species.

Animal pollinators enhance the reproduction of nearly 90% of flowering plants on Earth, including many food crops.

Pollinators are an essential component of insect and plant biodiversity. Bees are the standard carriers because they are usually present in large numbers and because they are the only group of pollinators that feed exclusively on nectar and pollinate throughout their lives.

For this study of blue orchard bees, scientifically known as Osmia lignaria, Galbraith, Rivers, and James Cane of the U.S. Department of Agriculture prepared nest blocks that contained a uniform number and sex ratio for adult bees before emergence.

Then they looked at the relationship between fire intensity and reproductive production, sex ratio and mass of offspring at a local scale (within 100 meters of blocks) and landscapes (750 meters). Female bees feed on both scales when caring for offspring.

“In fire-prone landscapes, there is variation in the species response to forest fires that preserve ecosystem structure and function,” said Rivers. “With blue orchard bees and similar species, the females foraging are investing in larger offspring and more females when more resources become available.”

The results showed that burnt mixed conifer forests provide fodder for blue orchard bees along a gradient of intensity, and that the increase in flower resources that comes after high-risk fires leads females to reallocate resources to the larger and more expensive sex – females – when nesting.

“Our study revealed more female offspring than is usually observed in blue orchard bees,” Galbraith said. “A greater proportion of females in areas surrounded by severely burned landscapes indicates an investment in more females due to greater availability of resources.”


The results have been published in ophthalmology. The Office of Land Management and the Ohio State University School of Forestry supported this research.

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