The effects of pesticides on the Asian honey bee (Apis cerana, shown above) have been understudied compared to their impact on Apis mellifera. A research team in Japan offers insights into toxicity levels of 11 common pesticides on Apis cerana. (Photo credit: Charles Lam, Flickr, CC-BY-SA-2.0.)

By Josh Lancette

In a recent Reddit AMA, honey bee experts May Berenbaum, Ph.D., and Gene Robinson, Ph.D., listed four P’s that drive problems with honey bees: pathogens, pesticides, parasites, and poor nutrition. In a recent study published in the Journal of Economic Entomology, researchers from Japan tested the effects of one of the P’s, pesticides, on the honey bee Apis cerana japonica, which the researchers refer to as the Japanese honey bee.

Josh Lancette

They tested 11 commonly used insecticides, including five of the controversial neonicotinoid class (often called neonics), using a technique known as an acute toxicity test, where a small amount of a pesticide is placed on the abdomen of each bee. Then, the researchers measured how many bees had died after 24 and 48 hours.

The results of the study showed that different pesticides had different effects, which is perhaps unsurprising. However, even different neonicotinoids had different levels of toxicity. For example, after both 24 and 48 hours, acetamiprid (a neonic) was the least toxic of the pesticides tested, while thiamethoxam and dinotefuran (also neonics) had the greatest toxicity after 24 and 48 hours, respectively.

The fact that nenoics had different levels of toxicity suggests that all neonics can’t be grouped together and classified as either good or bad. Rather, determining the positives and negatives of neonics depends on which specific neonic is used, how it is used, how much is used, for what reason it is used, and which species it contacts.

“Neonicotinoid pesticides should not be considered as a single group that acts uniformly on all honey bees,” write the researchers. “Careful management strategies are required to conserve A. cerana populations.”

Interestingly, A. cerana japonica, which is commonly found throughout Japan, was eight to 14 times more sensitive to pesticides than Apis mellifera, a honey bee found on every continent except Antarctica, has been found to be in other studies. The authors mention that most toxicity studies are performed on A. mellifera and that none have been performed on A. cerana japonica, meaning this study can serve as a start for customizing pesticide management practices in areas where A. cerana japonica and other A. cerana subspecies are present.

“Our toxicity bioassay data provide strong prima facie evidence that the broader ecological effects of some of these contaminants are more severe in A. cerana than those in A. mellifera,” write the authors. “This implies that pesticide management strategies in East Asian agricultural systems should be more site specific than those in other global regions, and these strategies should include application rate limits, more careful discrimination of specific uses for the different pesticides and more thorough testing of their effects on important non-target species.”

Josh Lancette is manager of publications at the Entomological Society of America.