A new study has found that when mason bees, a type of wild bee, are exposed to both pesticides and food scarcity, their reproduction drops 57%.
Loss of flowering plants and indiscriminate use of pesticides could seriously shrink mason bee and other wild bee populations, according to University of California-Davis researchers.
Entomologists say that's a big problem for farmers, who rely on native bees for pollination.
According to entomologists across the U.S., mason bees outperform other pollinators, including honey bees, in many different crops. Harm to mason bees means harm to agriculture, too, they say.
"Mason bees are amazing and under-appreciated little pollinators," said Katie Buckley, pollinator health coordinator at Washington State Department of Agriculture. "They deserve protection."
Clara Stuligross, a Ph.D. candidate in ecology at UC-Davis, is lead author of the study. She and her team conducted experiments this year with blue orchard bees, a type of mason bee.
Stuligross' team exposed the bees to the neonicotinoid insecticide imidacloprid, which is widely used.
The researchers found that the bees exposed to pesticides, especially those in cages with fewer wildflowers, delayed nesting, nested for less time and had fewer female offspring.
Females are important in the mason bee world, said Stuligross. Females are the ones that lay eggs, collect all the pollen and nectar and construct the nest.
But females also have a longer lifespan and eat more than males do, so in the bee economy, males are "less expensive" to raise.
When under stress from pesticides and limited food resources, Stuligross said, the bees in her study appeared to intentionally produce fewer females.
In bee biology, an unfertilized egg will become male and a fertilized egg will become female. Stuligross said the bees in her study chose to fertilize fewer eggs.
"It's pretty amazing they can do that, huh?" said Stuligross.
Fewer females mean less crop pollination — and less reproduction.
"In the bee world, males don't matter so much. Male numbers rarely limit population growth, but fewer females will reduce the reproductive potential of subsequent generations," said the study's co-author, Neal Williams, a pollination ecologist and professor at UC-Davis.
The researchers said there are several ways farmers can help protect mason bees.
First, they suggest farmers plant wildflowers in areas without pesticides or risk of pesticide drift.
Second, they suggest farmers who use pesticides always apply pesticides after bloom when the exposure risk is lower for bees.
They suggest researchers also consider altering the type of pesticides they use. Plants absorb long-lasting "systemic" pesticides like the neonicotinoid insecticide imidacloprid used in this study and output those toxins through all tissues and parts of the plant, including pollen and nectar. Systemic pesticides, they say, are dangerous to bees.
"I think the message is just to be more aware of the stressors to beneficial insects, bees especially, and do what we can to help," Stuligross.