Implementing an evolutionary framework for understanding genetic relationships of phenotypically defined insect biotypes in the invasive soybean aphid (Aphis glycines)

Abstract

Adaptive evolution of pest insects in response to the introduction of resistant cultivars is well documented and commonly results in virulent (i.e., capable of feeding upon resistant cultivars) insect populations being labeled as distinct biotypes. Phenotypically defined, biotypes frequently remain evolutionarily indistinct, resulting in ineffective application of virulence control measures and shorter durability of resistant cultivars. Here, we utilize an evolutionary framework to discern the genetic relationship between biotypes of the soybean aphid (Aphis glycines, Matsumura). The soybean aphid is invasive in North America and is among the most destructive pests of commercial soybean on the continent. Attempts to breed host-plant-resistant soybean have been hampered by the emergence of virulent aphid biotypes that are unaffected by the plant's resistance mechanism(s). Comparative population genetic analysis of virulent and avirulent (i.e., unable to feed on resistant cultivars) biotypes found populations to be genetically indistinguishable across biotype and geographic distance, with high rates of interpopulation immigration and admixture. The lack of genetic distinction between biotypes coupled with elevated genotypic diversity within all populations suggested virulence has a nongenetic-based or includes a gene complex that is widely distributed throughout soybean aphid populations, which undergo regular dispersal and unimpeded sexual recombination.

The Use of Refuge in Host Plant Resistance Systems for the Control of Virulent Biotype Adaptation in the Soybean Aphid (Hemiptera: Aphididae)

“…Field assessments have estimated percent virulence at Յ20% (Michel et al 2011, Wenger andMichel 2013), though, in a few instances, these Þeld populations have exceeded economic thresholds in single Rag varieties (Hesler et al 2013). A smaller virulent proportion in Þeld populations may decrease the likelihood of interbiotype competition in susceptible refuges, negating the ampliÞed Þtness advantage of biotype 3 (Donaldson et al 2007).…”

Soybean aphid intrabiotype variability based on colonization of specific soybean genotypes

“…Soybean aphid virulence variation within a local region has been hypothesized to be caused by nongenetic sources, such as phenotypic plasticity, endosymbiont association, cyclic asexuality, prior host, and environmental stress (Wenger & Michel, ). Wenger and Michel () also stated the likelihood that the evolution of quantitative virulence variability in A. glycines could be promoted during the coevolution with Rag genes and other resistance factors present in the host.…”

Complex patterns of global spread in invasive insects: eco-evolutionary and management consequences

“…In addition to differentiation in host (plant or insect) use, differences in phenology among distinct types appear important to maintaining separation. There are several examples of the arrival of a genotype or species that is morphologically similar to individuals in an already invaded area that has resulted in additional damage, increased niche breadth, or that has confounded management (Perring 2001;Saltonstall 2002;Peccoud et al 2008;Garnas et al 2012;Mapondera et al 2012;Wenger and Michel 2013;Shadmany et al 2015). For example, distinct host races of the pea aphid (Acyrthosiphon pisum) feeding on pea and broad bean, alfalfa and red clover in Chile are descended from biotypes in Europe (rather than evolving in situ; Peccoud et al 2008).…”