Insecticide Combo Packs Mighty Punch

An insecticide combo can deliver a knockout punch.

A cocktail of insecticides containing a plant protein and a common insecticide may be more lethal to crop pests than either ingredient used alone, according to university and USDA biologists. The one-two punch also inhibits the insects’ growth rate and reduces their chance of developing resistance.

One of those insecticides, Bacillus thuringiensis (Bt), is commonly used around the world. But researchers say some insects always survive the ordeal and over time, subsequent populations could develop resistance to the toxin.

The other insecticide that the group — from Penn State University, Mississippi State University, and USDA — is studying is Mir1-CP, a unique plant-based insecticide developed from certain strains of corn from Antigua. Unlike Bt, Mir1-CP breaks down proteins in a protective membrane covering the midgut. This membrane acts as a barrier that protects the caterpillar from toxins in the diet, and cycles nutrients to the midgut.

When the researchers added the two insecticides together, the mixture killed 61 percent of corn earworms and 57 percent of tobacco budworms, which is more than 10 times better than either by itself. Researchers saw similar results against the fall armyworm and the southwest corn borer, when the insecticides were used at slightly different strengths.

In addition to a high mortality rate among the insects, the study indicates a significant decrease in the growth rate of the survivors.

The research suggests strains of corn that naturally produce Mir1-CP could be cross-bred with other strains of corn that produce Bt to develop new varieties that are more effective against pests.

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