Commonly Used Pesticide Turns Honey Bees into ‘Picky Eaters’

Since 2006, bee­keep­ers in North America and Europe have lost about one-third of their man­aged bee colonies each year due to “colony col­lapse dis­or­der.” While the exact cause is unknown, researchers believe pes­ti­cides have con­tributed to this decline. One group of crop pes­ti­cides, called “neon­i­coti­noids,” has received par­tic­u­lar atten­tion from bee­keep­ers and researchers.

The UC San Diego biol­o­gists focused their study on a spe­cific neon­i­coti­noid known as “imi­da­clo­prid,” which has been banned for use in cer­tain crops in some European coun­tries and is being increas­ingly scru­ti­nized in the United States.

“In 2006, it was the sixth most com­monly used pes­ti­cide in California and is sold for agri­cul­tural and home gar­den use,” said James Nieh, a pro­fes­sor of biol­ogy at UC San Diego who headed the research project with grad­u­ate stu­dent Daren Eiri, the first author of the study. “It is known to affect bee learn­ing and memory.”

The two biol­o­gists found in their exper­i­ments that honey bees treated with a small, sin­gle dose of imi­da­clo­prid, com­pa­ra­ble to what they would receive in nec­tar, became “picky eaters.”

“In other words, the bees pre­ferred to only feed on sweeter nec­tar and refused nec­tars of lower sweet­ness that they would nor­mally feed on and that would have pro­vided impor­tant sus­te­nance for the colony,” said Eiri. “In addi­tion, bees typ­i­cally recruit their nest­mates to good food with wag­gle dances, and we dis­cov­ered that the treated bees also danced less.”

The two researchers point out that honey bees that pre­fer only very sweet foods can dra­mat­i­cally reduce the amount of resources brought back to the colony. Further reduc­tions in their food stores can occur when bees no longer com­mu­ni­cate to their kin the loca­tion of the food source.

“Exposure to amounts of pes­ti­cide for­merly con­sid­ered safe may neg­a­tively affect the health of honey bee colonies,” said Nieh.

To test how the pref­er­ence of sug­ary sources changed due to imi­da­clo­prid, the sci­en­tists indi­vid­u­ally har­nessed the bees so only their heads could move. By stim­u­lat­ing the bees’ anten­nae with sugar water, the researchers were able to deter­mine at what con­cen­tra­tions the sugar water was reward­ing enough to feed on. Using an ascend­ing range of sugar water from 0 to 50 per­cent, the researchers touched the anten­nae of each bee to see if it extended its mouth­parts. Bees that were treated with imi­da­clo­prid were less will­ing to feed on low con­cen­tra­tions of sugar water than those that were not treated.

The biol­o­gists also observed how the pes­ti­cide affected the bees’ com­mu­ni­ca­tion sys­tem. Bees com­mu­ni­cate to each other the loca­tion of a food source by per­form­ing wag­gle dances. The num­ber of wag­gle dances per­formed indi­cates the attrac­tive­ness of the reward and cor­re­sponds to the num­ber of nest­mates recruited to good food.

“Remarkably, bees that fed on the pes­ti­cide reduced the num­ber of their wag­gle dances between four­fold and ten­fold,” said Eiri. “And in some cases, the affected bees stopped danc­ing completely.”

The two sci­en­tists said their dis­cov­er­ies not only have impli­ca­tions for how pes­ti­cides are applied and used in bee-pollinated crops, but pro­vide an addi­tional chem­i­cal tool that can be used by other researchers study­ing the neural con­trol of honey bee behav­ior. The study was funded by the North American Pollinator Protection Campaign and the National Science Foundation.

Source: University of California – San Diego Release