Corn rootworm resistance to transgenic crops has become a growing concern for farmers, but a new study may bring us one step closer to another option for controlling this adaptable pest.
Late last year, Corteva scientists confirmed that some populations of western corn rootworm beetle were resistant to the fourth type of commercially-available Bt protein designed to control them: Cry34Ab1/Cry35Ab1. The existence of resistance to Bt traits in corn rootworm populations raises the stakes when it comes to controlling these insects. Already, failure to control the beetle is estimated to lead to global economic losses of up to $1 billion, annually. Further erosion of our ability to control the pest could drive this figure much higher.
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Corn rootworm species (Western, Northern, and Southern) have been infamously difficult to control, developing resistance not only to chemical treatments and crop traits, but cultural practices. The western species, which covers much of the eastern Corn Belt, may lay its eggs in soybean fields, exploiting the common practice of rotating between corn and soybean to thwart the beetle. The northern species, on the other hand, will enter periods of prolonged slumber, emerging when the field is once more planted with corn years later. Fortunately, a recent study published in the June issue of the Journal of Economic Entomology provides hope that we can expand our arsenal against corn rootworm without harming other insects.
The June study, published by a research team from DuPont-Pioneer (now Corteva), focused on the insecticidal activity of a new protein compound called IPD072Aa. Unlike the current crop of Cry protein traits that come from the bacterium, Bacillus thuringiensis, IPD072Aa was discovered in a soil bacterium called Pseudomonas chlororaphis. Earlier research confirmed that not only was the new protein effective against western corn rootworm, but that none of the populations already resistant to the Cry proteins were resistant to IPD072Aa. So unlike the current line of Bt hybrids, which kill insects by creating holes in the insect gut lining, IPD072Aa represents a new mode of action lethal to rootworm.
The research team focused on how the new protein may affect a broader number of insect species. Eleven beetle and four butterfly/moth species were fed diets containing different levels of IPD072Aa. Western corn rootworm died at higher rates when fed a diet containing the protein, and closely-related beetle species had lower-than-average adult weights. The effect of IPD072Aa appeared to diminish the more distantly-related a species was to western corn rootworm, however. For example, while southern corn rootworm experienced some weight loss, European corn borer, a moth pest of corn, did not.
Having a greater effect on western corn rootworm than other species would be a significant benefit for a new line of crop traits. Concerns over the effect of systemic pesticides, like neonicotinoids, and insecticidal traits on non-target insects (e.g., honey bees), make targeted pesticides much more attractive. The research team hopes that further testing will show that IPD072Aa has potential as a targeted pest management tool for corn rootworm management.
If safe for non-target organisms, IPD072Aa may be a helpful arrow in the quiver for fighting western corn rootworm damage. The novel mode of action and lack of non-target effects make the new protein a promising candidate as we search for alternatives to control the Cry-resistant populations of rootworm beetles. The possibility that even more insecticidal compounds exist in bacteria like P. chlororaphis provides hope that other effective management strategies are waiting to be found.
Contact Scott Williams, DTN Entomologist, at firstname.lastname@example.org.
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