Challenges to conservation biological control on the High Plains: 150 years of evolutionary rescue

Conservation biological control (CBC) makes valuable contributions to productivity in High Plains agriculture. Despite some notable exceptions, CBC holds a wide range of potentially damaging pests under natural control, largely due to the actions of beneficial arthropod species that have endured more than a century of forced adaptation to an increasingly industrialized agricultural landscape. 'Evolutionary rescue' is a natural selection process whereby species evolve adaptations that enable them to survive environmental conditions that would have been lethal to their ancestors. This process has structured both pest populations and the guilds of natural enemies that help suppress them in our highly disturbed agroecosystems. Rescued beneficial species, by virtue of their abundance and successful evolutionary history, including some either accidentally or intentionally introduced, are those with the greatest potential for future adaptation in the face of changing cultural practices and the emergence of novel pests. I review some existing impediments to CBC (large-scale, synchronous monocultures, inadequate plant and insect diversity in the landscape, migratory pests, vulnerable crop cultivars that rescue pests, rather than their enemies, and insecticidal seed treatments). Compounding these problems are commercial interests and agricultural philosophies that tend to incentivize yield-maximization and short-term profits over long term farm sustainability and profitability. However, certain agronomic practices implemented recently have likely benefited CBC. These include improved host plant resistance in crop cultivars, the advent of Bt-protected crops (which have reduced pesticide applications), the adoption of no-till and reduced tillage practices, more advanced irrigation technologies, and the development of more selective pesticides that are safer for beneficial arthropods. Looking forward, two current trends may improve the efficacy of CBC in row crops; the increased adoption of cover crops as an alternative to chemfallow periods, and increasing public concern for preservation of pollinator habitat on public lands, which will also benefit predators and parasitoids.