Diamondback Moth Disarms Plants that Accumulate Selenium for Defense

A newly-discovered variety of the invasive diamondback moth, found in the foothills west of Fort Collins, has developed a tolerance to selenium, according to research done at Colorado State University.

The discovery provided important knowledge of how selenium, a trace element essential at low levels to human health and an important anti-carcinogen, that can, at high concentrations, influence an ecosystem through its toxicity. Moreover, insight was obtained into the potential ecological ramifications of the cultivation of selenium-enriched crop plants.

Selenium is toxic in higher doses, and plants can pull selenium from the soil for protection from herbivores, said Elizabeth Pilon-Smits, associate professor of biology at Colorado State who oversaw the research. However, this variety of diamondback moth has developed a tolerance to selenium and can feed on the plant prince’s plume, which accumulates high levels of selenium (known as a hyperaccumulator). The research team also discovered a selenium-tolerant parasitic wasp, which eats the selenium-enriched diamondback moth and also accumulates the toxic metalloid. The research was published in the November 2006 issue of "Current Biology."

"We were able to follow selenium in its different forms through the ecosystem, from prince’s plume to the diamondback moth to the selenium-tolerant wasp," said John Freeman, Colorado State postdoctoral researcher who worked on the research. "Because these insects adapt to environmental factors very quickly, we now have a greater understanding of how selenium moves through a native ecosystem."

Selenium is an essential component of enzymes in the human body that function as antioxidant enzymes which protect cells from free radicals and may help the body kill cancerous cells selectively. Selenium is most commonly ingested by humans through multi-vitamins and plants in various forms. Plants enriched in methyl-selenocysteine, a naturally occurring seleno-amino acid, would be an excellent way to provide healthy doses of selenium to humans and animals. Conversely, some soils contain excess levels of selenium, either naturally or due to or human activities.

"Plants that remove selenium from the soil are useful and already are being used for remediation of environments polluted with excess selenium," said Colin Quinn, a Colorado State graduate student who helped conduct the research.

While high levels of selenium are found in some areas of the western United States, other areas, such as the eastern United States, have very little selenium in the soil and animals are thus often selenium-deficient. Researchers believe that selenium-enriched anticarcinogenic crops may be a beneficial food source for livestock as well as people in selenium-depleted areas.