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Neonicotinoids for pest management

Evidence in support of neonics is impressive, if you take the time to understand it

honeybee on a canola flower

Another summer is over, another harvest is done and now the key decisions are starting to loom for next year’s crop. The canola page in the seed catalogue is open, but whether the varieties on display are OPs or hybrids, herbicide tolerant, Argentine or Polish, most of them will come with a seed coating containing an insecticide to ward off the flea beetles. Since the banning of lindane, the compound of choice is a neonicotinoid, a water-soluble systemic that makes the emerging plant poisonous to the beetles.

“The neonics are a class of insecticide introduced commercially in the early ’90s,” explains Cynthia Scott-Dupree, environmental scientist and chair of sustainable agriculture at the University of Guelph. “They can be used as foliar applications, in furrow, all sorts of different ways but the most important characteristic of the neonics is they’re water soluble so they can be systemic. This allows us to use them as seed treatments.”

This systemic capability is the strength of the neonicotinoid compounds. Canola’s principle pest, the tiny flea beetle, emerges from the ground in late April to early May, attacking the canola plants as they emerge and when the seedlings are especially vulnerable. This is when you really need the seed treatment.

“They’re excellent for insect pests that hit the crop early in its development,” Scott-Dupree says. “If the chemical exists in the plant, then it really reduces the potential impact at a very vulnerable point in the plant’s growth period, and that’s why they’re so valuable.”

Data from Agriculture and Agri-Food Canada bear this out. According to these findings, seed treatments reduced flea beetle damage anywhere from nine to 64 per cent when compared to untreated checks. The reduction in damage improved the crucial stand establishment from two to 75 per cent, plant weight from 100 to 900 per cent and overall yield anywhere from three to 100 per cent. Canola farmers really like those numbers so they’re ready to pay the few extra dollars for treated seed.

“Before neonics, the available seed treatment options for canola were things like Lindane, and it was a granular formulation,” says honeybee entomologist Rob Currie at the University of Manitoba. “The problem with that one is that some birds like burrowing owls would go and pick that up and it was toxic to them.”

In one study, bumblebees were put out when pollen was present in both conventional and organic corn crops. The result? The majority of the bees foraged on nightshade and not the corn pollen.
In one study, bumblebees were put out when pollen was present in both conventional and organic corn crops. The result? The majority of the bees foraged on nightshade and not the corn pollen. photo: File

Lindane, an organochlorine, was fairly persistent in the environment, it was carcinogenic, and 12 to 20 per cent of it would volatilize into the atmosphere to be carried somewhere else. In 2009 an international ban was imposed on Lindane, and its use in agriculture was discontinued. The neonicotinoids were there to take up the slack and, in many ways, they were better suited to the task.

“They attack nicotinoid receptors, and those same sort of receptors are unsusceptible in mammals and most other organisms,” Currie says. “They’re thought to be fairly safe for most non-target species, but really toxic to insects.”

“Another reason they’re considered safer when compared to older chemistries is because they retain their efficacy at smaller doses,” Scott-Dupree says. “When we talk of some of the older chemistries like the organophosphates you’re talking about applying pounds of product per hectare, but with the neonics, you’re talking about grams of product per hectare. They’re greener in that sense.”

The neonicotinoid insecticides are not without their detractors, and news of European bans, reports of bee killings and lawsuits by various industry and environmental groups have galvanized public opinion against them. Incidents in Germany and Ontario produced honeybee body counts, and the culprit in both cases was neonicotinoid seed treatments. Neonics have been fingered as a factor in colony collapse disorder, which involves the loss of entire hives due to unexplained behaviour.

It’s perfectly true that bees, as card-carrying members of class Insecta, die when exposed to toxic levels of an insecticide. It’s perfectly reasonable to assume too that the lab studies performed on bees exposed to nicotinoids are true, and that these levels can threaten pollinators and the beekeeping industry. Based on these studies and the public opposition to their use, many European governments have enacted bans on neonicotinoids, and there’s pressure to do that here as well.

“If you go back and look at some of the studies, they’re exposing the bees to extremely high rates of neonics to determine the levels of toxicity,” Scott-Dupree says. “So a lot of the media hoopla is based initially on the laboratory studies to see if they do get an effect. If they don’t get an effect it could be that they’re not using the right experimental protocol and their study isn’t working.”

The lab studies are the first step in a longer process. This is where we determine the actual levels of a toxin required to kill the bees, because the first rule of toxicology is that it’s the dose that makes the poison. For example, analysis of apples shows that they contain cyanide, which is a deadly poison that will kill you if you get a big enough dose of it. In fact, the natural world is rife with different toxins, poisons and venoms which most of us survive because the concentrations are so low that our bodies can filter and metabolize them with no ill effect.

This isn’t good enough for some critics, and just the knowledge that there’s cyanide in apples might be enough for some people to swear off them, even if one a day keeps the doctor away.

This phenomenon is called intuitive toxicology, and it’s made worse by hyper-accurate analysis that can detect microscopic concentrations of any compound. Still, the real question is, will the concentrations in the field be high enough to cause trouble with the bees?

“I’ve done three or four field studies on this now and, although you find residues in the nectar and pollen, the levels are extremely low, way below the level where there is any observable effect,” Scott-Dupree says. “There are residues there, but you have to make sure the dose is there to cause the problem, and you have to make sure that the route of exposure exists so the bee can come in contact with the toxin.”

And that’s the story with the bee kills in Germany and Ontario, where the source of the toxin was treated corn seed. Corn is a species of grass so it doesn’t need an insect pollinator. Additionally, studies by Scott-Dupree and Chris Cutler showed that bees, in this case bumblebees, don’t forage in corn for the pollen.

“We put the bumblebees out when pollen shed started in both conventional and organic crops, and in both situations, bees didn’t forage on the corn pollen,” Scott-Dupree says. “In three out of eight fields they did forage for corn pollen but the highest amount collected was not more then 3.6 per cent. Most of them foraged on bittersweet nightshade, a common weedy plant found in hedgerows all over the place.”

In Ontario and Germany, the actual route of exposure was not the pollen but the seed itself under unusual circumstances. The conditions were dry, windy and warm, and the bees were foraging in adjacent fields. The pneumatic seeders would jostle the seeds around in the pipes, which knocked some of the insecticide coating off. This was blown into the dry soil and produced a toxic dust cloud that drifted into the bees’ range and killed large numbers of them.

“It’s a completely different issue, a different route of exposure,” Scott-Dupree says, who adds “They’re doing a lot of work on mitigating that by using new fluency lubricants and add-ons to the seed drills to prevent dust from flying up into the air.”

Still, in light of the corn seeding incident, there is talk of tightening the rules regarding neonic application so producers may be required to prove that they need them before they’re allowed to use them. Considering the principles of Integrated Pest Management, where you use pesticides as needed rather than as insurance, this may sound perfectly reasonable. However, it may not work with a seed treatment aimed at early-season infesters, or with root pests that are almost impossible to scout and spray for.

“They have to order their treated seed in the fall the year before they plant, and there’s really no way a grower can tell this fall what the pest pressure is going to be next year,” Scott-Dupree says. “So most of them will use the seed treatment, which is relatively low cost in terms of input costs per hectare. They’ll use it as insurance.”

Although it’s unlikely that we’ll see an outright ban on neonicotinoids in Canada, the European Union imposed a two-year restriction on them in 2013. Eight nations opposed the ban, claiming the science was incomplete.

“They’re still having some problems with bees, even though that product has been banned, so clearly that’s not all of the issues associated with bee deaths,” Currie says. “I think a lot of the problems they’re having with bees are related to things like parasitic mites, viruses and other pathogens, so to put all the blame on that particular insecticide is a bit unfair.”

“Some people think I’m pro neonics but I’m really pro seed treatment. I think they’re an excellent method of applying an insecticide. It’s very targeted and it’s much more beneficial than using a foliar application from a plane,” Scott-Dupree says. “It’s also good for the land, because the less you run back and forth over the soil and compacting it, the better for the environment.”

This article first appeared as “The neonic choice” in the October 2014 issue of Country Guide

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