Do Pesticides Kill Bees?

Honeybee pesticide

No one can deny the critical importance of bees, and by extension, all other pollinators. Over 80% of the world’s plants rely upon pollinators for their reproduction. So, if you were to answer the question ‘do pesticides kill bees’ your kneejerk reaction would be ‘of course’, after all pesticides are supposed to kill insects, right?

It’s not quite that simple.

I attended a symposium on pollinators a while back. The attendees present in this hotel conference room basically boiled down into five groups: the bee experts from the state university that were hosting the event, local farmers who need bees to pollinate their crops, the commercial beekeepers that supplied those bees, the usual group of environmentalists, and lawn care people like myself.

The mood in the room was tense; the beekeepers were mad at the farmers because the farmers used pesticides on their crops just before the bees showed up to pollinate, the farmers were mad at the beekeepers for being mad at them, the environmentalists were mad because, well, they’re environmentalists, and everyone was mad at the lawn care people because everyone is always mad at the lawn care people. You kind of get used to this stuff after a while.

After a number of fascinating presentations by the bee experts, it was discussion time. Oh, boy. The finger pointing was intense all around the room. After a while, the professor from the state university finally put everyone in their place. He told the beekeepers that they need to be much better stewards of their hives, paying closer attention to the myriad stresses of travel, nutrition and pests that infest their hives. He told the farmers that they need to be much more attentive and to communicate with the beekeepers what they apply to their crops. And finally, he told the environmentalists to stop picking on the lawn care people – they are the least of our problems. That comment completely made my day.

So, what’s going on with bees?

Saying all pesticides kill bees is not accurate and is a distraction from the efforts to reveal the underlying problem, which may or may not have anything to do with pesticides. When we use the word “pesticide” we mean it as a blanket term covering any product used to control an unwanted organism, such as herbicides that control unwanted weeds, fungicides that thwart virulent fungi, insecticides that act against destructive insects and in the special case of caring for honeybees, miticides for control of the Varroa mite, the single most destructive pest of honeybees worldwide.

The Varroa mite, known to science as Varroa destructor (how’s that for a name?), is an introduced arachnid more closely related to spiders than insects. First identified in Florida in the late 1980’s, they have steadily spread throughout the United States, and can also be found in most other countries. Varroa not only feeds upon the blood of honeybees, it also introduces viruses and bacteria that cause catastrophic diseases in hives as well. If you were to ask me what one factor affecting overall honeybee health is paramount, I would have to say that it is the Varroa mite.

Pesticides are not uniformly toxic to bees and other pollinators, and insecticides are not the only threat; researchers have shown that other pesticides used in agriculture encountered by bees can have a synergistic effect, being more toxic in combination than if encountered singly, sometimes exponentially so.

However, this is a problem that is borne overwhelmingly by production agriculture where commercial honeybee operations are essential to the pollination of crops. Truckload after truckload of hives crisscross the nation pollinating one crop after another. Problems associated with commercial beekeeping make the jump to native populations of bees with devastating effects. Researchers all around the world are working at solving this difficult and multifaceted problem.

How does caring for my lawn affect bees?

As it turns out, turfgrasses do not require pollinators in order to reproduce, however many of the common weeds in lawns either do require pollinators or their flowers attract them. In caring for our lawns, we do have the need for insecticides to control a short list of insects that will cause damage, so the potential exists for exposure.

Know your pests.

Just because an insect is present in a lawn does not necessarily mean that it will cause noticeable damage. Each turfgrass insect has a population range in which it can be tolerated without intervention with pesticides. For instance, a healthy lawn can withstand between 15 and 20 chinch bugs per square foot and between 8 and 10 white grubs (depending upon the exact species) per square foot.

It’s also important to understand the lifecycle of each insect. Using a pesticide to control an insect when it’s fully grown is generally less effective than attempting to control them right after they hatch.

Know your pest control products

As time goes by, pesticides used on lawns have become evermore selective in what they control, and what they leave behind. An insecticide used thirty years ago to control white grubs would also have a huge impact on any bees that came into contact with it, while today we can choose a product that is not only far more effective in controlling white grubs, it is all but non-toxic to bees.

Some insecticides have a very narrow window in which they must be applied in order to be effective. For instance, most preventive grub control products need to be applied in advance of the egg hatch; applying them once the grubs have started feeding usually results in poor control.

Last but certainly not least, the most important step you can take to protect bees and other pollinators in your landscape is to read and fully understand the label directions for any pesticide that you intend to apply. Stewardship of non-target species like bees is one of the most important aspects of the label. Usually, you can ensure the safety of bees by simply watering the product into the soil after application or avoiding application during times of day when bees are expected to be present in the landscape.

In any case, with a little planning and good technique, you can keep your lawn safe from damaging insects while at the same time protecting pollinators.

Click to learn more about pollinator protection

- Bob Mann, Agronomist