By Andrew Porterfield
Honey bees are crucial for pollination and crop production worldwide. But since episodes of Colony Collapse Disorder began arising in the mid-2000s (and have subsided somewhat), the causes of costly deaths of adult bees have focused on mites, viruses, and a number of pesticides.
One group of pesticides, the neonicotinoids, has been singled out for regulatory action in several European countries, and regulation is under consideration in the United States. Most of the studies that were conducted previously gathered their data from topical applications of the test chemicals, by testing only the active ingredients, or by using artificial feeders with the pesticide in a sugar solution, none of which provide appropriate measures of the amounts of pesticide exposure in the field.
In September, however, researchers from the U.S. Department of Agriculture’s Agricultural Research Service and Mississippi State University reported that they tested 42 commonly used pesticides in a more realistic field setting on cotton row crops. They essentially mimicked a situation where an adult bee in a cotton field accidentally gets sprayed. Furthermore, the researchers used pesticides that were in the actual commercial formulations that would be used by farmers in their fields. This is an important distinction because most previous research tested the active ingredients only, which did not include other chemicals that influence the distribution, absorption, and overall exposure of the pesticides to plants and bees. Their work appears in the Journal of Economic Entomology.
Using a modified spray tower to simulate field spray conditions, the researchers found that 26 pesticides, including many (but not all) neonicotinoids, organophosphates, and pyrethroids killed nearly all of the bees that came into contact with the test pesticide sprays. However, seven pesticides, including glyphosate and one neonicotinoid (acetamiprid), killed practically no bees in the tests.
The pesticides tested included 40 insecticides and miticides, one herbicide (glyphosate, better known by its trade name “Roundup”), and one fungicide (tetraconazole). What made this study more realistic was not only the field spray application of each pesticide, but also the interpretation of data. The researchers determined the lethal concentration and lethal dose of each pesticide (to determine chemical toxicity), and then matched those numbers with the amounts of pesticide actually used in agriculture. In this way, they could rank pesticides by individual chemical toxicity as well as by how much they are used in the field. Chemicals that were not used as much ranked lower despite toxicity, while chemicals that were used more tended to rank higher.
The majority of row crops in the U.S., such as cotton, soybeans, and corn, are transgenic, which has reduced the harm from chewing insects, but has refocused pesticide applications to target sucking insects. These pests include the tarnished plant bug (Lygus lineolaris) and various species of stink bugs. This refocus, together with an increase in resistance to insecticides by some targeted insects, led to more widespread use of leaf sprays of insecticides. That practice, in turn, has boosted the risk of honey bee exposure to these pesticides.
The new data show that a number of pesticides are available, including the neonicotinoid acetamiprid, that could be used to control tarnished plant bugs, stink bugs, aphids, and mites, without causing much (if any) harm to bees. It also calls into question some regulatory measures that focus only on neonicotinoids, since organophosphates, pyrethroids, and carbamates together comprise the 26 commercial pesticides that pose a significant threat to honey bees. Also significant was the low-toxicity ranking of glyphosate, the world’s most-used pesticide, which has been targeted for its use on fields with genetically modified “Roundup-ready” crops that can resist the herbicide.
A number of surprises also appeared in the study. First, an insecticide called sulfoxaflor was found to be near the middle in terms of toxicity. This is important because the EPA’s approval of sulfoxaflor was recently overturned by the U.S. Ninth Circuit Court of Appeals. In fact, it was found to be less toxic to bees than permethrin, a pyrethroid insecticide that is used in agriculture, household pesticide products, flea shampoos for pets, and in head lice products for people.
Also, four pesticides (methoxyfenozide+spinetoram, carbaryl, indoxacarb, and 1-cyhalothrin+chlorantraniliprole) that had been considered moderately toxic to bees were found to be higher risk when field-application concentrations were considered. Finally, one pesticide, gamma-cyhalothrin, which was considered to be a high-risk chemical, was found to be only an intermediate risk because its field use rate was relatively low.
Field spraying of insecticides and other pesticides may effectively kill insects, including valuable honey bees, and the risk to honey bees can be reduced by selecting pesticides with lower toxicity in field applications. This study determined that a number of pesticides, including a neonicotinoid, showed little to no toxicity to bees, meaning they could be effective alternatives to organophosphates, carbamates, and other neonicotinoids. According to the authors, “Our data, particularly the ratios of field application rates to lethal concentrations of each pesticide, provide a quantifying scale to help extension specialists and farmers with pesticide selection to maintain effective control of target pests and minimize the risk to foraging honey bees as well.”
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Andrew Porterfield is a writer, editor and communications consultant for academic institutions, companies and non-profits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield on Twitter, or visit his Facebook page.