Crop rotation is an ancient and ecologically benign agricultural technique that limits pest populations while replenishing depleted soil. It is still common today, and corn farms in the US and Europe often rotate between planting corn and soybeans to confound the western corn rootworm (WCR), Diabrotica virgifera virgifera, which devastates corn plants but generally cannot digest soy. Recently, however, some populations of WCR have shown resilience to crop rotation, feeding and ovipositing on soybeans as well as corn.

Scientists are still exploring the mechanisms behind this adaptation, and some research indicates that the gut microbiota facilitates soybean digestion in rotation-resistant WCRs. Now, a team of researchers led by Manfredo Seufferheld (University of Illinois, Champaign) has turned to genetics to better understand this adaptation (Evol. Appl. doi:10.1111/eva.12278; published online 28 May 2015).

“The evolution of resistance in insects is complex,” Seufferheld said in a press release; “human activity, the evolutionary history of the insects, the host and non-host plants, the microbial community and the genes all play a role.”

Seufferheld's team collected WCRs from several populations with different phenotypes, including wild-type and rotation-resistant, and fed different diets to WCRs of each phenotype. They provided some with a typical corn diet and others with soybean diets and then removed their guts for analysis.

The researchers found that wild-type and rotation-resistant WCRs expressed similar genes in their guts when both types were fed corn, but different genes when fed soybean diets. In total, they identified 3,973 genes that are differentially expressed in the guts of wild-type and rotation-resistant WCRs in at least one dietary condition.

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In their analysis, they determined that many of these genes are associated with assorted physiological processes including growth and immune responses. “We also found differentially regulated genes involved in detoxification and genes involved in transport of metabolic products, lipids, sterols and drugs in and out of the cell,” Seufferheld said.

The emerging picture provides no immediate and simple explanation of rotation resistance in WCRs, but it illustrates the complex situational adaptations that can create a resistant population. Though WCRs are a particular bane of the agricultural industry, the evolution of resistance is a topic of concern of many fields. As conventional measures for biological control yield increasingly resilient pests in fields, barns, labs and hospitals, researchers must continue to investigate how resistance emerges in controlled populations.