Controlling forest insects with Mimic®

The pesticide Mimic® is an insect growth regulator used to control leaf-eating insects that cause damage or death in trees. Tebufenozide is the active ingredient in the formulation, which controls forest defoliator pests such as gypsy moths, tent caterpillars, budworms, tussock moths and loopers. These are all pests of the Lepidoptera order.

Mimic has been reviewed and approved by both Health Canada’s Pest Management Regulatory Agency and the U.S. Environmental Protection Agency.

The registered formulation of Mimic (labelled Mimic 240 LV in Canada) is 25% tebufenozide. The other components are glycerol, canola oil and water.

Mimic imitates a natural insect hormone

When ingested by Lepidoptera larvae, Mimic imitates a natural insect hormone that causes the developing caterpillars to molt prematurely as the larvae go through their growth stages. The caterpillars then quickly stop feeding and die.

Approval under NAFTA as a reduced-risk pesticide

Mimic 240 LV was one of the first pesticides simultaneously reviewed by Health Canada’s Pest Management Regulatory Agency and the U.S. Environmental Protection Agency under the North American Free Trade Agreement’s Joint Review Program for Reduced-Risk Pesticides.

More than 200 tests and studies were conducted for presentation to the regulatory agencies. These tests and studies were carried out by researchers in universities, government-funded institutions and private organizations to generate the data required for registration purposes.

The studies show that Mimic is not harmful to humans when it is used according to label instructions for forest pest management, including in aerial applications.

Mimic supports integrated pest management in forestry

Mimic does not directly affect beneficial insects such as wasps, mites and spiders, all of which help keep forest insect pest populations in check. It affects lepidopteran larvae only. This makes it is especially suitable for Integrated Pest Management programs in forestry.

Non-target lepidopterans (moths and butterflies) can be affected by aerial application of Mimic, but only if they are in the larval stage during or shortly after an application (within a few weeks), and only if they eat foliage that has insecticide residue on it.

Managing risks with Mimic use

Studies show that when Mimic reduces Lepidoptera larvae (such as the spruce budworm) in a forest, the indirect effects on animals that eat Lepidoptera larvae are small. For example, reductions in food supply for forest birds were found to be short term and had no overall effects on bird reproduction or population.

As well, Mimic poses little or no measurable risk to bees, birds, fish, mammals and non-lepidopteran insects. It also has no impact upon shrimp, crayfish and lobsters.

Mimic adheres strongly to soil particles until it is reduced by microbial and chemical actions. It is therefore almost immobile in soil, with low risk of leaching into water.

Field studies show that Mimic poses minimal risks to water fleas and other aquatic microcrustaceans when it is used according to label instructions.  However, microcrustaceans can be harmed if concentrations and exposure durations are greater than expected under operational conditions (e.g., accidental spill).

Aerial application is not permitted over open water

Aerial application of Mimic over open water bodies (including ponds and streams) is not permitted. If Mimic does reach water bodies, the residue may remain for a few weeks in aquatic sediments. Most sediment-dwelling invertebrates are at low risk of effects from Mimic because they are not affected even at worst-case expected environmental concentrations.

An exception is midges (non-biting fly larvae), which have been shown to be susceptible to low concentrations of Mimic. However, this group of sediment-dwelling invertebrates is naturally very resilient and can rapidly recover from disturbances (a fact shown by how often they are associated with polluted waters). That factor – combined with applications not being allowed over water bodies, the low likelihood of Mimic residues reaching water surfaces, and the dilution effect before residues can reach sediments – reduces the risk of significant impacts on midge populations.