Researchers at Oregon State University said they recently discovered that the blue orchard bee produces a great number of female offspring in the aftermath of forest fires. Researchers added the more severe the fire had been, the greater percentage of females, more than 10% greater in the most badly burned areas relative to areas that burned the least severely.


“This is one of the first studies that has looked at how forest fire severity influences bee demography,” said Jim Rivers, an animal ecologist with the OSU College of Forestry. “Sex ratio varied under different fire conditions but the number of young produced did not, which indicates bees altered the sex of their offspring depending on the degree of fire severity.”

Female bees control the sex of their offspring, laying eggs fertilized with sperm that become females, or non-fertilized eggs that become males. Bees pollinate many of the flowering plants that make up the food chain as well as native ecosystems. Researchers said understanding how fire – expected to increase in frequency and severity – influences their reproductive outputs is an important part of knowing how post-fire management actions could help or harm bees.


“We placed bees on different sites within recently burned mixed-conifer forest in southwestern Oregon and used them as a measuring stick to tell us how good the bee habitat was,” said Sara Galbraith, a postdoctoral researcher in the College of Forestry. “Adjusting offspring production toward the more expensive offspring sex shows a functional response to changes in habitat quality via an increased density of flowering plants.”

In general, pollinators benefit from canopy-reducing fires in dense conifer forest ecosystems; flowering plant abundance usually increases for several years following a fire, resulting in food resources that enhance wild bee diversity and abundance.

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