The soybean aphid will always win the numbers game. Each year, aphid populations can produce multiple generations within a growing season in the same field, which makes them especially good at evolving resistance to insecticides. Now scientists have discovered that a large variety of aphid biotypes can exist in any given year, and those types can vary widely from year to year — which gives the pest a leg up in overcoming resistant soybean varieties as well.
The discovery comes from a new study produced by scientists from a dozen universities, seed companies, and government institutions. The researchers used 9 soybean lines with various Rag genes, a type of gene that gives soybean plants aphid resistance. Between 2004 and 2006, the aphid rapidly developed resistance to an aphid-resistant soybean line with the Rag1 gene, and this study set out to find out why.
For 3 years, the researchers plucked naturally occurring soybean aphid populations from 9 Midwestern states and one Canadian province and tested them on the nine different aphid-resistant soybean lines. “The occurrence of soybean aphid biotypes was highly variable from year to year and across environments,” the scientists concluded, which means the pest has far more genetic diversity than previously known.
Several factors likely contribute to this variability, including:
- aphids’ migratory patterns,
- internal genetic diversity
- ability to reproduce asexually, and
- abundance of buckthorn, which they overwinter on.
Controlling the aphid with naturally resistant soybean lines will clearly never be simple, but the scientists did note that one variety with a pyramid of Rag1c and Rag4 genes had the lowest frequency of aphid colonization.
For more information, see the scientists’ study here: bit.ly/1IUyUnI.