Pollinators, Potted Plants & Pesticides

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As the current issues of the Minnesota Conservation Volunteer and Land Stewardship Letter make clear, pollinators are the kinds of keystone critters we all can play a role in helping—or hurting. As I realized while producing LSP podcasts (episodes 54 and 60) on the subject, everyone from beekeepers to entomologists agree on that one. We need to keep that in mind even when doing things that are seemingly unrelated to the lives of bugs. For example, when buying a potted plant or figuring out how to control the growing emerald ash borer menace, we may want to think twice about the unintended consequences when it comes to the health of our apian workhorses.

Every third bite of food is directly or indirectly connected to the work of pollinators. And wild habitats such a native prairies wouldn’t be quite the same if bees and other bugs weren’t hauling pollen from plant-to-plant.

That’s why scientists are frantically trying to figure out why honeybees seem to be suffering so much from Colony Collapse Disorder and other maladies these days. And why are their wild cousins in decline as well (including here in Minnesota)? Is it habitat loss, feedlot beekeeping, introduced diseases or the stress of becoming the insect version of migrant workers by being transported across the country to custom-pollinate almond groves? Or is it, as University of Minnesota bee expert Marla Spivak believes, a complicated combination of factors?

One part of the mix that cannot be ignored is pesticides, which have dogged wild and domestic pollinators since they became ubiquitous after World War II. Bees and other pollinators are notoriously sensitive to pesticide poisoning. And because bees are natural born collectors, they often bring chemical contaminants back to their hives.

A Penn State study released in 2008 showed that low levels of over 70 pesticides and metabolites of those pesticides were present in hives. Most of them were common insecticides and herbicides, including atrazine, used in agriculture and around the home. Penn State researchers are particularly concerned that when the pesticides combine in a hive, they can have a synergistic effect hundreds of times more toxic than any of the pesticides individually.

The good news is that labeling restrictions (no spraying during the middle of the day when bees are most likely to be foraging) and a transition to chemicals of lower toxicity have made it less likely bees will be outright killed by spraying. Iowa’s agriculture department recently released a new “Bee Rule” that limits applications of insecticides labeled as dangerous to bees. In areas near registered Iowa apiaries, applications must occur prior to 8 a.m. and after 6 p.m., according to the rule.

However, research has shown that a new class of pesticides could offer a more insidious threat to bees and other pollinators. In recent years, organophosphate insecticides, which are toxic to mammals and birds, have been replaced by a class of pesticides called neonicotinyls. Derived from nicotine (yes, the same stuff that makes your body crave Marlboros and Copenhagen), these bug killers are systemic, meaning they are put on a plant’s seed, or injected straight into the roots or stem. They work their way up to the leaves, killing insect pests that feed on the plant.

The advantages to these kinds of bug killers are many: for one thing farmers, greenhouse keepers and homeowners aren’t spraying toxins in the open air, reducing the chance of the chemical going where it’s not supposed to. In addition, it works specifically on insects, offering little threat to other creatures, including humans. That’s the main reason neonicotinyls have become one of the most widely used pesticides—particularly in greenhouses, by landscape companies and in homes. If you bought a potted plant recently, likely it’s been fortified with neonicotinyl.

“I can’t impress on you how common this is on everything,”  U of M entomologist Vera Krischik told me recently, adding that these types of pesticides can stay in a plant for up to a year.

A few years ago Krischik noticed that after feeding on some potted plants that were in her backyard, bumblebees would become disoriented, and fall to the ground where they would suffer from tremors before dying: a classic sign of neonicotinyl poisoning.

She did follow-up research and found that plants containing the neonicotinyl insecticide imidacloprid caused high death rates in beneficial insects like pink lady beetles, green lacewings and parasitic wasps. Krischik is now taking steps to study more thoroughly the impacts these pesticides have on bees that feed on plant nectar and pollen.

The effects of neonicotinyl insecticides such as imidacloprid on local non-target species such as bees is of particular interest now that the emerald ash borer, a devastating killer of ash trees, has arrived in the Minnesota and other Midwestern states. This class of pesticides is one borer-control tool being promoted by tree experts.

“This pesticide isn’t all bad. It’s just not a good idea if it finds its way into plants insects use for nectar,” says Krischik.

Some uses of neonicotinyl insecticides were banned in France and Germany after honeybee die-offs were blamed on the chemical, but it’s too early to tell if these restrictions will help bee populations bounce back, say entomologists.

Spivak says it’s unlikely pesticides are the only cause of CCD or other mass bee die-offs. Typically in a CCD situation, one colony will collapse and a neighboring one won’t, although the bees often forage in the same areas where pesticides were applied.

“But the pesticides are a problem,” the entomologist told me. “And we need to pay attention to them, whether they are the root of the problem or not.”

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