Pesticide is known to cause population decline in bees but the extent it has over time is still not fully understood.
Clara Stuligross and Neal M. Williams of the University of California say the chemicals may produce carryover effects that influence reproduction and population dynamics over time.
The researchers state: “Global insect declines are profoundly concerning, especially for groups like bees that provide important services to humanity.
“Pesticide exposure, both directly to foraging bees and via carryover effects from past exposure, dramatically reduced bee reproduction, which reduced population growth.
“Carryover effects reduced bee reproduction by 20% beyond current impacts on foraging bees, exacerbating the negative impact on population growth rates.”
This indicates that bees may require multiple generations to recover from a single pesticide exposure.
Pesticides are linked to global insect declines, with impacts on biodiversity and essential ecosystems.
The researchers found that the combined threats reduced blue orchard bee reproduction by 57 per cent and resulted in fewer female offspring.
“Just like humans, bees don’t face one single stress or threat,” said lead author Clara Stuligross, a Ph.D. candidate in ecology at UC Davis.
“Understanding how multiple stressors interplay is really important, especially for bee populations in agricultural systems, where wild bees are commonly exposed to pesticides and food can be scarce.”
The study found that pesticide exposure had the greatest impact on nesting activity and the number of offspring the bees produced. Pesticide exposure reduced bee reproduction 1.75 times more than limiting their food.
The team conducted their research by exposing the blue orchard bee to the neonicotinoid insecticide imidacloprid, the most widely used neonicotinoid in the United States. It’s also among the most frequently applied insecticides in California.
The study authors said the research can help farmers make decisions about how they manage the environment around orchards.
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