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COUNTRY LIFE IN BC • OCTOBER 2017


Pollinator response to insecticides come under scrutiny Neonicotinoids are the world's most widely used pesticides


Did you know that about one in three mouthfuls of food we eat depends on the unmanaged pollination services of bees? Almost 90%


Research by MARGARET EVANS


of flowering plants depend on animals for pollination. The services they provide to global agriculture are valued up to US$577 billion. But both the abundance


and diversity of pollinators are in serious decline. In Europe, nearly 10% of bee species are threatened and bumblebees worldwide are declining. It’s no wonder there is growing concern this may lead to a less


varied, nutritionally challenged diet. Along with the stresses of habitat loss disease, parasites, invasive species and climate change, a leading cause for the crisis is exposure to insecticides, which is having a significant impact on bumblebee colonies. A recent study on


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colony-founding bumblebee queens showed that after exposure to thiamethoxam, a neonicotinoid insecticide, queens were less likely to form a colony resulting in a 26% reduction in the proportion of queens that laid eggs. “We have been working on thiamethoxam for some years now because of the different ways the pesticides are being applied,” says professor Nigel Raine, Rebanks Family Chair in Pollinator Conservation at the School of Environmental Sciences, University of Guelph, ON. “They are sprayed on the field and, if it happens during flowering, bees make contact on the surface of the flowers. Neonicotinoids are being used extensively, especially in many of the large-scale field crops like corn, soy, canola and wheat. The pesticide is [also] put onto the surface of the seed coating and they are planted into the ground. These compounds are incredibly water soluble and they are taken up as the plant germinates and grows. So, you have the pesticide in the plant as it grows and several months later when the plant flowers there are still residues found in the nectar and the pollen that the bees have


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been consuming. It is low concentrations but it is consumed every time the bees feed on the nectar and the flower and when they feed it to their offspring.” Bumblebees are solitary.


Raine says that the queens go through a critical part of their life cycle when they hibernate and overwinter alone, look for a nest site alone, find nectar and pollen, produce wax to make nests, lay eggs, then brood them like mother birds – all the time alone.


Stressful


“It’s a stressful time for bumblebee queens and we were interested in


understanding the potential impact of insecticide exposure at that critical period in the life history,” he says. In the study, the queens


were individually exposed to field-relevant levels of


thiamethoxam as well as two natural stressors including a parasite and varying hibernation durations. It was the exposure to thiamethoxam that caused the 26% reduction in the proportion of queens that laid eggs. The research results were published in the journal Nature Ecology and Evolution. With this large percentile


reduction in establishing a next-generation colony, the population dynamics going forward dramatically increase the likelihood of extinction and the study clearly showed that neonicotinoids were the negative drivers in this critical egg-laying stage in a bumblebee’s life. Of great importance is the


fact that it is not only the treated crop fields that are hazardous but surrounding natural flowering plants. “You don’t just have the


bees sampling pollen from different crops,” says Raine. “They are also sampling many wild flowers. We traditionally thought the insecticides were restricted to the treated crops but they are turning up in the other plants around the fields. Some of the root movement could be windblown from dust at planting time but the majority is probably from water in the soil. The insecticide is very water soluble and estimates of what is put on the seed and what is recovered from treated crops is that only two to 20% actually gets into the crop. There is a question about


where the rest is going. Sunlight and other organisms can break down these products and some goes into the soil and stays there for quite a long time. But some of it is moving around in water and being taken up by other plants, particularly under drought conditions. These wild plants around the margins are really attractive to pollinators like bumblebees so you might extend the period to which they are exposed to these insecticides beyond the bloom period of the crop itself. When talking about chronic exposure, that’s the area we need to know much more about.”


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Neonicotinoids are the most widely used class of pesticide worldwide and thiamethoxam is one of three neonicotinoids under a European Union moratorium for flowering bee-attractive crops. “Ontario has taken a lead in


restricting the use of the same three neonicotinoids including thiamethoxam used on corn and soy,” says Raine. “More recently, Health Canada has said that they are proposing to phase out one of these chemicals based on the residues that have been found in watercourses.”


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