Top Crop Manager

Features Insecticides Seed & Chemical
The ‘buzz’ about insecticides


November 30, 1999
By Treena Hein

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Crop farmers, and well-informed members of the general public, know that the use of agricultural chemicals is needed to prevent insects from eating the crop. However, no one wants to negatively impact the environment, put anyone’s health at risk or contribute to the decline of pollinators. The annual economic value of honeybees alone in pollinating Canadian crops is estimated to be about $1.5 billion. “Many crops require pollination, so we have to find a balance,” says Dr. Cynthia Scott-Dupree, a professor in the School of Environmental Science at the University of Guelph, who researches the effects of pesticides on bees. “We must continue to develop ways to have pollinators stay healthy but manage pests, as well.”

Bee mortality has hit a crisis level across North America during the last few years, but Scott-Dupree says there is no evidence to suggest insecticides are the primary cause. “Agricultural pesticides have been used pervasively for the last six decades, but we’ve never seen bee losses like we’re seeing now,” she notes.

Indeed, she says at the same time that active ingredients of insecticides have become more toxic (so less is needed to achieve the same level of pest control), they have also become more specific in terms of targeting pest insects only. “These advances, combined with new application methods, can reduce the impact on non-target beneficial insects such as bees, as well as on the environment in terms of things like water quality and soil microflora,” she observes. “If pesticides are used correctly from the start, we can ensure that there is minimal environmental impact in the long term.”

Anecdotally, bees seem to be doing better in 2010 in terms of mortality compared to the past several years, says Paul Kozak, provincial apiarist for the Ontario Ministry of Agriculture, Food and Rural Affairs. “We have no hard data at this point in the year, but will have survey results later in the season,” he says. Kozak notes that bees in Ontario do not display “colony collapse disorder” as it is defined in the US, but that, “During the last six years, we’ve seen a lot of colony mortality, and during the last three years, it’s been three times above what is normal.”

The bee research community in Canada, Kozak says, is in agreement about the main factor behind this die-off, which is Varroa mite infestation. However, the studies of Dr. Ernesto Guzman, a professor in the School of Environmental Science and head of the Honeybee Research Centre at the University of Guelph, show that beekeeper management is also playing an important part. “The second and third most significant factors after Varroa mite were low bee populations in colonies before winter and low food reserves before winter,” Guzman observes. “This is due to some keepers splitting colonies too much and not providing enough food reserves for colonies to survive the cold.”

Guzman says Nosema fungus did not play a significant role in bee mortality in his studies, but did restrain colony population growth during spring.

Whatever the causes of bee mortality, Pierre Petelle, director of regulatory affairs at CropLife Canada, says his organization well understands the agriculture industry’s strong reliance on a healthy pollinator community. CropLife Canada is the trade association representing the manufacturers, developers and distributors of pest control products and plant biotechnology. “Our association members remain very supportive of activities to improve the health of bees and other pollinators,” he says. “Our industry is being implored to come up with additional tools to help control the Varroa mite, and so in the end, pesticides will be part of the solution to helping bees rebound.”

Best practices and future outlook
To minimize potential negative impacts on beneficial non-target insects such as bees, Petelle says crop farmers should always read and follow all label directions and observe restrictions and precautions. “This means reducing spray drift by avoiding application on windy days and respecting time-of-day application recommendations to avoid spraying during the day when bees are foraging,” he notes.

Kozak also recommends that farmers contact nearby landowners and beekeepers to discuss spraying. “Beekeepers also need to take the initiative to be in contact with their farming neighbours,” he says. “In addition, farmers should do their best to select chemicals that are less toxic to bees” (see chart on page 28).

There is also excitement in both the agricultural and beekeeping communities about the use of seed treatments that can, in some instances, replace foliar spraying. “Many chemicals are toxic when sprayed, but not always when used as seed treatments,” says Scott-Dupree. “If you can use treated seeds, do it.”

With seed treatments, the insecticide level in the plant tissue is still high enough to effectively control early season pests, but is very low by the time the plants flower, and bees come around to collect nectar and pollen. “My research has shown that residue from seed treatments, without fail, is very low at the time of flower,” says Scott-Dupree. “Typically residues do not approach concentrations in the nectar and pollen of the flowers to cause significant behavioural changes and mortality in bees.”

However, seed treatments can only be derived from “systemic” insecticides, those that possess higher water solubility than other chemicals and can travel throughout the plant as it grows. Scott-Dupree says a relatively new class of insecticides known as neonicotinioids “fit the bill,” yet they have been a major concern to beekeepers due to the toxicity of some of them to bees. “They can be used as seed treatment for corn, cotton, canola and sunflowers as well as a contact or foliar insecticide for various crops and pests,” she notes.  

In terms of other systemic low-toxicity insecticides that have potential as seed treatments, Scott-Dupree says companies are working with some of the second-generation diamides. Dr. Paul Hoekstra, technical registrations manager for human and environmental exposure at Syngenta Crop Protection, says his company has two or three promising seed treatment candidates under development that will help control such key pests as flea beetles in canola and aphids in pulses and soybeans. “We’re building on the success of our Cruiser line of seed treatments, which provide early-to-mid-season control of soybean aphid,” he says.

In June, Bayer Cop Science introduced Raxil WW seed treatment, specially designed to protect cereal crops against wireworm damage that is becoming a greater problem across Western Canada. “This year,” says communications manager Derrick Rozdeba, “we also introduced Trilex AL seed treatment for pulse crops and soybeans.”

Relative toxicity of foliar insecticides to honeybees
(Source: OMAFRA fact sheet “Prevent Bee Poisoning” at www.omafra.gov.on.ca/english/food/inspection/bees/bee-poisoning.htm )