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Aphids put out welcome mat for other pests

IOWA STATE (US) — Aphids not only have a unique ability to block the genetic defense response of soybeans, but they may also open the door for other pests to do even more damage to crops.

A new study finds that the tiny insects that have become a primary threat in Iowa in recent years, can essentially short-circuit the hormonal defense mechanism in soybeans meant to combat insect infestations.  That change may make it easier for other pests, such as the soybean cyst nematode, to colonize the plant as well.

“After about seven days, a successful aphid infestation can hijack the plant’s defense response. The soybean plant initially puts up a defense, but that response is gone after about a week,” says Gustavo MacIntosh, associate professor of biochemistry, biophysics, and molecular biology at Iowa State University.

Aphids emerged as a serious threat to Iowa soybeans around 2000. The insects are native to Asia and most likely came to the United States on international travelers or plants brought into the country.  In the years since, aphids have caused soybean farmers major headaches, reducing yields in affected fields by up to 40 percent, MacIntosh says. Their presence in a field may require farmers to have insecticides applied, increasing the costs of crop production.

Published in the journal Molecular Plant-Microbe Interactions, the study focused on the effect aphids have on soybeans after prolonged infestation. The presence of aphids initially activates a biological defense mechanism in soybeans, but a successful aphid infestation blocks the soybean plant’s natural defenses in about a week by making the plant think that it’s experiencing environmental stress, he says.

When that happens, the soybean plant goes through a number of changes, from its leaves all the way to its roots. These changes explain why aphids make plants more susceptible to soybean cyst nematode infection, as shown previously in research MacIntosh conducted with the laboratories of Matt O’Neal, associate professor of entomology, and Greg Tylka, professor of plant pathology and microbiology.

The increased susceptibility to nematodes after an aphid infestation even occurred in soybean varieties that are genetically resistant to the soybean cyst nematode, Tylka says.

“The nematodes reproduce better if there is a successful aphid infestation. On the other hand, nematodes have a negative effect on aphid populations,” Macintosh says. “This seems to be a rare relationship between different species of pests.”

The researchers hope the findings will lead to soybean varieties that are more resistant to aphids and other pests. The work may also help to predict the response of soybeans when new pests arise in the future and ultimately lead to more consistent soybean production that is more profitable for farmers.

Graduate student Matthew Studham is a co-author on the study that was funded by grants from the Iowa Soybean Association and the ISU Plant Sciences Institute.

Source: Iowa State University

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  1. michele

    Why they do that?In the ” struggle for life” this is illogical because is better to have a privileged access to food

  2. Ian

    Just a heads up: the picture associated with this article is of a plant bug (Hemiptera: Miridae) rather than an aphid. See http://myrmecos.wordpress.com/2009/09/21/faq-the-illinois-aphid-swarm/ for a decent picture of a soybean aphid (others are certainly out there too).

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