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Title: Genetics, synergists, and age affect insecticide sensitivity of the honey bee, Apis mellifera

Author
item RINKEVICH, FRANK - Louisiana State University Agcenter
item MARGOTTA, JOSEPH - Louisiana State University Agcenter
item PITTMAN, JEAN - Louisiana State University Agcenter
item Danka, Robert
item TARVER, MATTHEW - Former ARS Employee
item OTTEA, JAMES - Louisiana State University Agcenter
item HEALY, KRISTEN - Louisiana State University Agcenter

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/16/2015
Publication Date: 10/2/2015
Citation: Rinkevich, F.D., Margotta, J.W., Pittman, J., Danka, R.G., Tarver, M.R., Ottea, J.A., Healy, K.B. 2015. Genetics, synergists, and age affect insecticide sensitivity of the honey bee, Apis mellifera. PLoS One. doi:10.1371/journal/pone.0139841.

Interpretive Summary: High rates of mortality of honey bee colonies in the United States raise the threat that the beekeeping industry is becoming economically unstable and may fail to provide needed crop pollination services. The potential role of insecticides in colony mortality has garnered much attention, and determining the toxicities of these compounds to honey bees is vital to help understand the risk that they pose. Some factors which are not normally considered in toxicity studies are the type and age of the bees used, and how interactions with other chemicals in the hive (pesticide synergists, and chemicals used to treat parasitic mites) affect toxicity responses. This investigation determined that several commonly used types of honey bees (Carniolan, Italian, and Russian) differed in their responses. Italian bees generally were the most sensitive, but this varied among different classes of insecticide. The age of bees affected sensitivity, but the responses differed with different insecticides; older bees were more sensitive to one compound but less sensitive to another. An insecticide commonly used for mosquito control was more toxic when combined with a standard synergist as expected, but also when in the presence of compounds used as in-hive mite treatments. The findings point to the need for consideration of the genetic background and age of bees being tested when toxicity data are to be used for assessing risks of pesticides to honey bees.

Technical Abstract: The number of honey bee colonies in the United States has declined to half of its peak level in the 1940s, and colonies lost over the winter have reached levels that are becoming economically unstable. While the causes of these losses are numerous and the interaction between them is very complex, the role of insecticides has garnered much attention. As a result, there is a need to better understand the risk of insecticides to bees, leading to more studies on both toxicity and exposure. While much research has been conducted on insecticides and bees, there have been very limited studies to elucidate the role that bee genotype and age has on the toxicity of these insecticides. The goal of this study was to determine if there are differences in insecticide sensitivity between honey bees of different genetic backgrounds (Carniolan, Italian, and Russian stocks) and assess if insecticide sensitivity varies with age. We found that Italian bees were the most sensitive of these stocks to insecticides, but variation was largely dependent on the class of insecticide tested. Synergism bioassays with piperonyl butoxide, amitraz, and coumaphos showed increased phenothrin sensitivity in all stocks, but also demonstrated further physiological differences between stocks. In addition, as bees aged, the sensitivity to phenothrin decreased, but the sensitivity to naled increased. These results demonstrate the variation arising from the genetic background and physiological transitions in honey bees as they age. This information can be used to determine risk assessment, as well as establishing baseline data for future comparisons to explain the variation in toxicity differences for honey bees reported in the literature.