UNIVERSITY PARK, PA
Farmers who use certain pesticides to kill insects and fungi on their crops may also be destroying their honeybees.
Research completed by Penn State and University of Florida show four common pesticides and an inactive chemical often used as a pesticide additive (NMP) are highly toxic to honeybee larvae. In addition, the research found that the negative effects of the pesticides can be greater when found in combination within the hive.
That's a problem, the researchers point out, since pesticide safety is judged almost entirely on adult honeybee sensitivity and does not consider mixtures of pesticides. The risk assessment process that the Environmental Protection Agency uses should be changed, they contend.
Previous research by the team showed forager bees return to the hive with pollen that includes, on average, six different pesticides. In the hive, nurse bees use the contaminated pollen to make the beebread they feed to honeybee larvae.
The researchers included Penn State professors of entomology Jim Frazier and Chris Mullin; Wanyi Zhu, graduate research assistant in entomology; and Daniel Schmehl, University of Florida postdoctoral associate in entomology and nematology.
The team focused on four common pesticides: fluvalinate, coumaphos, chlorothalonil and chlorpyrifos.
Fluvalinate is an insecticide/miticide marketed under several names including Apistan, while Coumaphos is a miticide/insecticide used as a livestock dip, dust or spray.
Chlorothalonil is a fungicide marketed under several names including Bravo. It is a broad-spectrum agricultural fungicide often applied to crops in bloom when honeybees are present for pollination because it is currently classified as safe to bees
Chlorpyrifos is a widely used insecticide in crop management, marketed under several brands including Lorsban, while NMP (N-methyl-2ppyrrolidone) is added to pesticides to help them spread and penetrate the target plants or animals pests.
Fluvalinate and coumaphos are commonly used by beekeepers on crops to control Varroa mites. The compounds persist within beehives for about five years.
The research team raised honeybee larvae in their laboratory, feeding them beebread treated with a single pesticide and mixtures of all the pesticides. They also added seven concentrations of NMP to a royal jelly diet made from pollen.
The treated diets, containing different types and concentrations of chemicals, were fed to the laboratory-raised bee larvae. The research showed that mixtures of pesticides can have greater consequences for larval toxicity than are expected from individual pesticides.
Of the four pesticides, the larvae were most sensitive to chlorothalonil, while a mixture of chlorothalonil and fluvalinate also had negative affects.
The larvae were also sensitive to chlorothalonil and the miticide coumaphos. In contrast, they noted, the addition of coumaphos significantly reduced the toxicity of the fluvalinate and chlorothalonil mixture.
The research team also documented that increasing amounts of NMP corresponded to increased larval mortality, even at the lowest concentration tested.
The pesticides may kill by directly poisoning the larvae or indirectly through inadequate nutrition by disrupting the beneficial fungi that are essential for nurse bees to process pollen into beebread. Either way, researchers pointed out, chronic exposure to pesticides during the early life state of a honeybee has a resulting impact on the survival and development of the entire bee brood.
The findings suggest that the common pesticides, individually or in mixtures, have statistically significant impacts on honeybee larval survivorship. The study is the first to report serious toxic effects on developing honeybee larvae of dietary pesticides in concentrations that currently occur in hives.
The research was funded by the National Honey Board, the U.S. Department of Agriculture-National Institute of Food and Agriculture-Agriculture and Food Research Initiative-Coordinated Agricultural Products and the Foundational Award program.