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Codling moths in Washington currently do not appear to be carrying resistance traits to the insecticides commonly used to control them, but researchers are a step closer to being able to identify that resistance quickly if and when it develops.

Three key insecticides have been used effectively in the region for codling moth control, but the possibility of the insects becoming resistant to these chemicals is a growing concern for orchardists.

A study by research geneticist Stephen Garczynski of the USDA Agricultural Research Service in Wapato, Washington, aimed to identify the codling moth’s proteins that are targeted by each of these insecticides and to identify potential detoxification enzymes in them that could lead to resistance.

Rather than using a laboratory colony of codling moths for the study, Garczynski and the research team gathered insects from the wild in the Yakima Valley.

The study showed there don’t appear to be any resistance changes in codling moths currently, he told the Washington Tree Fruit Research Commission at the Apple Crop Protection Research Review, held in January in Wenatchee, Washington.

“We’ve gotten a lot of information. We can’t say what’s going to cause resistance,” he said. “But we’ve provided all the targets and all of the enzymes so that we have these tools now to be able to determine resistance more rapidly than if we were starting from scratch, should the need arise. I’m hoping it doesn’t arise.”

Research results

The researchers worked to identify codling moth gene transcripts that are elevated in response to sublethal doses of three insecticides — the anthranilic diamide Altacor, the spinosad Delegate, and the neonicotinoid Calypso.

Altacor (chlorantraniliprole), targets the ryanodine receptor in the insect, a protein that is important in nerve and muscle function. Another insect, the diamondback moth, develops a point mutation that causes a single amino acid to change.

That change is associated with resistance to a chemical that also targets its ryanodine receptor. The researchers identified the ryanodine receptor in the codling moth, then cloned and sequenced the region in the diamondback moth.

The researchers are working to develop a PCR assay that can be used to monitor for a similar mutation in codling moths that could lead to resistance, Garczynski said.

Delegate (spinetoram) targets nicotinic acetylcholine receptors that are key to the nervous system of the codling moth. Two different mutations have been found to confer resistance to spinosads, identified in mutations in the Western flower thrip and the silkworm.

Calypso (thiacloprid) also targets nicotinic acetylcholine receptors. Mutations in the brown leafhopper and the green peach aphid have resulted in resistance to neonicotinoids.

The researchers identified the location of the mutations that result in resistance to both spinosads and neonicotinoids, cloned and sequenced them, and developed PCR assays to monitor for similar mutations in codling moths that could confer resistance to the insecticides, he said.

Another way a codling moth can develop resistance is through an enzyme change that detoxifies the chemical control agent.

The researchers have identified the three major classes of detoxification enzymes in codling moths and cloned and sequenced some of them. Garczynski said PCR assays will be used in the future to quickly determine if resistant insects are using these enzymes to detoxify the insecticides. •

– by Shannon Dininny