"This feeding assay is significant. This gives us a way to test these toxins," said Christie Williams, a co-author of the findings and a research scientist with the USDA Agricultural Research Service Crop Production and Pest Control Research Unit working in Purdue Entomology.

"A preliminary chemical assay might give us promising results. But then you could go to all the trouble of making a transgenic plant based on that chemical test and have it not work."

To get the toxins into the fly larvae, the scientists allowed Hessian flies to lay eggs on the leaves of seedling wheat plants. When the eggs hatched, the plants were taken from the soil, their roots cleaned and trimmed, and then replanted as hydroponics with the toxic proteins added to the plants' water.

"The plant is just acting like a big straw taking up the toxins," Williams said. "It's just like putting a carnation into a cup of colored water and watching the flower change colors."

When the fly larvae attacked and fed as usual, they were also ingesting the toxins that were taken up through the water.

"We knew they would feed on the plant," said Subhashree Subramanyam, a Purdue agronomy research associate. "So we used the plant as the translocation medium."

Protein immunoblot detection tests, which use antibodies to detect the presence of a particular protein, showed that the larvae had ingested the toxins added to the water.

The team tested nine lectins — anti-nutrient proteins that disrupt digestive function. In particular, Hessian fly larvae responded to snowdrop lectin, which comes from snowdrop bulbs, a flowering plant.

Larvae that ingested the snowdrop lectin developed only half as fast as the control larvae. There was also evidence of disruption of the microvilli — fingerlike extensions in the midgut that aid in nutrient uptake.

"It is possible that snowdrop lectin, by itself, could give wheat better resistance to the Hessian fly," Shukle said.

The scientists plan to have a transgenic version of the wheat developed for further testing. The USDA funded their work.