Neonicotinoid insecticide causes bees to abandon their young at night: study – Science News

Spying on bumblebees as they nest has revealed strange behaviour in those exposed to tiny amounts of a widely used pesticide.

A study published in the journal Science found bees exposed to an insecticide called imidacloprid were less likely to feed and care for their larvae, and spent more time hanging out around the edges of the nest.

According to study lead author and Harvard University biologist James Crall, the most surprising and puzzling finding was that the effect on bee behaviour was strongest at night.

“If you look overnight, it’s totally striking,” Dr Crall said.

“Oftentimes the majority or all of a colony [affected by imidaclorprid] will be immobile — which you never see in healthy colonies.

Imidacloprid belongs to a clbad of insecticides called neonicotinoids (also called “neonics”, which is a lot easier to say).

Chemically similar to nicotine, these are highly effective insecticides that interfere with an insect’s nervous system.

There has been an ongoing and bitter dispute over the evidence that neonic use affects bees badly in the field.

This year the European Union announced it would ban the outdoor use of three insecticides in this clbad, including imidacloprid.

Bee barcodes

For their study, Dr Crall and team filmed the behaviour of 12 colonies of the Bombus impatiens species of bumblebee in the lab, each for five minutes, 12 times a day for two weeks.

They tracked the movement of the bees by attaching tiny paper tags to their backs, which were marked with a number and a barcode.

“It’s like a really simple QR code,” Dr Crall, who developed the computer tracking software, said.

The bees were allowed to forage in adjacent chambers, some of which contained pesticide-laden nectar.

Separate to their lab study, Dr Crall and team also studied how the pesticide affected colonies in the field.

Normally, bumblebees build an insulating wax “canopy” to keep their brood protected from the cold.

But bees exposed to imidacloprid were less likely to construct canopies compared to their healthy counterparts, and were less able to control the nest’s temperature.

‘Unprecedented detail’ in study

An Australian expert who also studies the impact of neonics on bees said the study provided unprecedented detail.

“This is the first time that we’ve used this method to look at the effect of a compound like this inside the colony on brood rearing,” Andrew Barron of Macquarie University — and who was not involved in the new research — said.

He said the level of pesticide used in the study was tiny — about 10 parts per billion.

While the new study is in bumblebees, Dr Barron said it was “not unreasonable” to badume there are similar effects in other bee species.

“In terms of the neurobiology of bees and brain structures, they’re all really quite similar,” Dr Barron said.

And, he said, the consequences of bees spending less time caring for their young would be lower larval survival and slower colony growth.

“That would line up with what we’ve seen with pesticide impacts on both honey bees and bumblebees.”

Evidence of how neonics affect bees is complex, not least because the same dose of pesticide can have different effects on the same species depending on their location.

But Dr Barron said this just suggests the effects of pesticide involves interaction with other factors such as the local environment.

He emphasised the majority of studies have shown low doses have adverse effects on bee behaviour, including their ability to forage.

Bees under threat?

Apart from pesticides and other pollutants, bees around the world face a multitude of environmental risks, which include diseases such as those caused by the varroa mite as well as lack of food.

According to authorities, Australian honey bee populations are not in decline.

But the same cannot be said of our native bees, according to University of Adelaide bee behaviour expert Katja Hogendoorn, who was not involved with the study.

Native bees also play an important role in pollination — in crops as well as native plants.

Dr Hogendoorn said there is little research on our native bees, so we don’t know whether numbers are increasing or decreasing.

But Dr Hogendoorn also said studies in the US and Europe have shown native bee populations have halved. Similar figures are likely in agricultural areas in Australia due to the removal of native vegetation, as well as pesticide use.

Over half of native bee species don’t forage on introduced plants, which means native bees in agricultural areas are at risk of malnutrition, Dr Hogendoorn said.

And while beekeepers can move their honey bee hives to avoid pesticide exposure, unmanaged native bees that nest in trees are more vulnerable.

“Native bees forage about 300 metres around their nest, so unlike honey bees, they cannot dilute the effects of pesticides by foraging far and wide,” Dr Hogendoorn said.

Nigel Raine of the University of Guelph in Canada points to another reason why native bees may be at greater risk.

While bumblebees and honey bees live in colonies, the effects described in the new study could be more severe in what are known as “solitary” bees, he wrote in a commentary also published in Science.

Solitary bees make up the majority of the 20,000 bee species in the world, and most of Australia’s native bee species.

In solitary bees, Dr Raine wrote, females are “overworked single mothers”, solely responsible for raising their brood.

This would make it “more likely that a small behavioural change as a result of pesticide exposure might have a measurable impact on their ability to produce as many high quality offspring”.

Where to now for neonics?

Despite concern by beekeepers and others in Australia, the Australian Pesticides and Veterinary Medicines Authority (APVMA) has no plans to review the insecticide’s use in the wake of the European ban decision.

“Given that Australian honey bee health is good, there is no cause for similar restrictions here,” the regulator states on its website, although it will continue to monitor the issue.

The APVMA also states that the National Residue Survey, which tests animal and plant products, has found no traces of neonics in any honey products tested.

But Dr Barron says his own research with CSIRO has found negative impacts on bees from neonics at just five parts per billion.

This is well below the 10 parts per billion level tested for by the National Residue Survey.

Like Dr Barron, Dr Hogendoorn argued that more judicious use of neonics is in order.

“Neonics are a very useful tool and in many cases better than other things, but they need to be used very carefully,” she said.

Dr Barron said if a pesticide is banned and replaced with another insecticide, it’s not necessarily going to be a better situation.

While not calling for an agricultural ban, Dr Hogendoorn said such insecticides should be avoided in home gardens.

This year Australian retailers announced they would voluntarily withdraw sale of the neonic-containing Confidor to home gardeners.

The manufacturer of Confidor refers to the APVMA website, which states neonics-based products are “safe when used according to the label directions”.

But Dr Hogendoorn said we need the results on specific research on the impact of neonics use, also in combination with other pesticides, in the Australian environment.

She added it is also important to look at the impact of such pesticides on other beneficial organisms in the environment, which feed on pests and reduce the need to spray in the first place.