Friday, March 29, 2024

Crop spray disrupts bee learning, memory

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Honetbees suffer severe learning and memory deficits after ingesting very small doses of the pesticide chlorpyrifos, potentially threatening their success and survival, new Otago University research suggests. In their study, researchers from the Departments of Zoology and Chemistry collected bees from 51 hives at 17 sites in Otago and measured their chlorpyrifos levels. They detected low levels of pesticide in bees at three of the 17 sites and in six of the 51 hives they examined.
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Most uses of the chemical were being banned in Britain from April 1. Cereal crops growers said they would face an uphill battle to protect their crops from pests.

After April 1 its use would be limited to a protected brassica seedling drench treatment.

Detecting chlorpyrifos in the bees was not a surprise to the Otago researchers.

In 2013, Associate Professor Kim Hageman and her team from Otago’s Department of Chemistry showed chlorpyrifos was detectable in air, water and plant samples and even in non-sprayed areas because it had a high ability to volatilise and travel great distances.

In the laboratory the researchers fed bees with similar amounts of the pesticide, which was used around the world to protect food crops against insects and mites, and put them through learning performance tests.

Study lead author Dr Elodie Urlacher said they found chlorpyrifos-fed bees had worse odour-learning abilities and also recalled odours more poorly later, even though the dose they ingested was considered to be "safe".

“For example, the dosed bees were less likely to respond specifically to an odour that was previously rewarded.

“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.”

Dr Elodie Urlacher

Otago University

“As honeybees rely on such memory mechanisms to target flowers, chlorpyrifos exposure may be stunting their effectiveness as nectar foragers and pollinators,” Urlacher said.

The study identified the threshold dose for sub-lethal effects of chlorpyrifos on odour-learning and recall as 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.”

The study was the first to establish the threshold at which a pesticide had an effect on memory specificity in bees while also measuring doses in bee populations in the field, she said.

“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.”

In Britain, Association of Independent Crop Consultants agronomist Sean Sparling told UK Farmers Weekly he hadn’t been a big user of chlorpyrifos but was disappointed by the manner and speed of its withdrawal.

“I wasn’t surprised, as it was only a matter of time, but there is virtually no use-up period and if we don’t get rid of it by April 1, it has to go back.

“I am also disappointed it has been taken away despite regulators saying we wouldn’t lose actives unless there was something equally as good to use in its place.”

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