The widespread use of chlorpyrifos, a highly neurotoxic organophosphate, could even threaten the success and survival of the honey producers, Otago University research suggests in a study published in the Journal of Chemical Ecology.
Though the results of the chemical’s use did not come as a surprise to lead researcher Kim Hagerman and her team, their study was the first to identify the threshold at which a pesticide has an effect on memory specificity in bees while also measuring doses in bee populations in the field.
In 2013, Associate Professor Hageman showed that chlorpyrifos was detectable in air, water, and plant samples, even in non-sprayed areas of New Zealand, due to the pesticide’s high ability to volatilise and travel great distances.
In their latest study, the team collected bees from 51 hives across 17 locations in the south of the country, detecting low levels of pesticide in bees at three of the sites and in six of the hives.
In the laboratory they then fed other bees with similar amounts of the pesticide and put them through learning performance tests.
The researchers found that the chlorpyrifos-fed bees had worse odour-learning abilities and also recalled smells more poorly later on, even though the dose they ingested was considered to be "safe".
“The dosed bees were less likely to respond specifically to an odour that was previously rewarded. As honeybees rely on such memory mechanisms to target flowers, chlorpyrifos exposure may be stunting their effectiveness as nectar foragers and pollinators,” said study lead author Elodie Urlacher.
The threshold dose for sub-lethal effects of chlorpyrifos on odour-learning and recall was found to be 50 picograms of chlorpyrifos ingested per bee.
“This amount is thousands of times lower than the lethal dose of pure chlorpyrifos, which is around 100 billionths of a gram. Also, it is in the low range of the levels we measured in bees in the field,” said Dr Urlacher.
“Our findings raise some challenging questions about regulating this pesticide’s use. It’s now clear that it is not just the lethal effects on bees that need to be taken into account, but also the serious sub-lethal ones at minute doses.”
Other research suggests that organophosphates like chlorpyrifos do not only affect bees adversely, and have documented how exposure to low levels during human pregnancy can impair learning, change brain function, and alter thyroid levels of offspring into adulthood.
Despite Prof. Hagerman’s team’s findings, a recent survey found that New Zealand’s honey bees were in a healthier position than their severely challenged cousins in the northern hemisphere.
Conducted by the Ministry of Primary Industries and various bee interest groups, the survey found that bee hive losses now stand at 11% in New Zealand, compared to 17% in the northern hemisphere. The findings, from 366 Kiwi beekeepers, reflect 40% of the industry.
Queen problems were the main contributing factor to the honey bee losses, the survey revealed.
The body representing the agricultural chemicals industry claimed the report showed that neonicotinoid insecticides, which have been blamed for bee losses in the northern hemisphere, were not a threat to hives.
“Overall, our bee population is thriving, which is good news especially after all of the over-dramatised aspersions on the state of our pollinators,” said Mark Ross, chief executive of Agcarm, which partially funded the research.
Source: Journal of Chemical Ecology
“Measurements of Chlorpyrifos Levels in Forager Bees and Comparison with Levels that Disrupt Honey Bee Odor-Mediated Learning under Laboratory Conditions.”
Authors: Elodie Urlacher, Coline Monchanin, Coraline Rivière, Freddie-Jeanne Richard, Christie Lombardi, Sue Michelsen-Heath, Kimberly J. Hageman, Alison R. Mercer