Insecticide Should Be Used Carefully

By Erik Skindrud, LSMP Editor

Imidacloprid may not kill bees outright, but research suggests it can disorient and disable them to the point where colonies lose the ability to collect food (as seen here) and reproduce.

You may not know Imidacloprid by name, but chances are you?EUR??,,????'?????<

Sold under the names Merit, Imicide and Marathon, Imidacloprid is sprayed on shrubs, injected into trees and applied directly to pets for flea control. More dilute formulations are available to consumers. More potent formulas are sold to landscape professionals.

Smoking Bugs Out

Imidacloprid is a kind of synthetic nicotine that kills insects by impairing normal nerve function. The good news is that the bug killer is much less toxic that substances like diazinon, which was withdrawn from residential use in 2004. New concerns about its effect on bees and other wildlife, however, reminds pesticide applicators to follow application guidelines and to use integrated pest management practices to keep use at a minimum.

Carpenter bees are generally a nuisance species that burrow into eaves and trees that are weakened by disease. Research shows, however, that bumblebees and other bee species are sensitive to insecticide applications. Photo by Guy Nelson

Bees Now a Concern

According to a recent label for Bayer Advanced Tree & Shrub Insect Control, the Imidacloprid-containing product should not be applied ?EUR??,,????'?????<

In France and Brazil, its use is on hold because a growing body of evidence suggests that Imidacloprid may be contributing to the worldwide decline of honeybees and related species. For the past five years, bee experts have been baffled and concerned by a drop-off in honeybee populations that is hitting commercial beekeepers and may soon affect the price of fruits and nuts that depend on bees for pollination.

Asking an Expert

Imidacloprid application is still legal for commercially-licensed applicators in the U.S. But in the light of its possible effects on bees, it now makes sense to limit the use of Imidacloprid formulations and to follow a set of guidelines that will limit its impact on bees and other beneficial insects.

Given the uncertainty, it makes sense to use caution when applying Imidacloprid. At a minimum, applicators should always ask themselves three questions when dealing with the product.

Prof. Eric Mussen of the University of California at Davis is recognized around the world as a leading bee expert. He has been interviewed extensively over the past two years about the world-wide decline of honeybees and related species.

Q & A

LSMP asked Dr. Eric Mussen of U.C. Davis?EUR??,,????'?????<

LSMP We?EUR??,,????'?????<

Still other studies, where Imidacloprid was fed for weeks to colonies at sub-lethal doses, but way above what would be encountered in the field, had no short term or long term negative effects on the bees.

A worker garbed in protective gear sprays fungicide on a tanoak tree in California. Similar procedures are used to treat trees with imidacloprid?EUR??,,????'?????<

LSMP Our readers use various Imidacloprid formulations and we?EUR??,,????'?????<

Our problem, here, is lack of information. How much Imidacloprid or major breakdown products should we expect from treated plants? Bayer says that the value for Imidacloprid is about 5 ppb in nectar from sunflower and canola.

UCR claims to have found 550 ppb in nectar from Eucalyptus trees (red gums) that had a soil treatment (Merit) around the roots to control lerp psyllids. There are no studies about what we call honeydew. That is the sugary sap that passes through sucking bugs and sometimes is collected by honey bees. If the chemical is in a high enough concentration to kill the sucking bugs, then wouldn?EUR??,,????'?????<

It is too soon to try to state that Imidacloprid is safe or unsafe around pollinators. However, it is safe to state that not enough research has been done on a chemical that is becoming almost ubiquitous in agricultural and urban settings.