All Is Not Lost: Fitness Costs Are Associated with Virulence in a Parthenogenetic Pest of Soybeans, and That’s Really Good News

Efforts to delay resistance by insect pests to plants that are resistant to them include a refuge of susceptible plants.  When combined with a high dose of the toxin, a refuge can prevent the frequency of resistant alleles from increasing. However, this is predicted not to occur when the target pest reproduces asexually unless a fitness cost is associated with resistance.  Working with the soybean aphid (Aphis glycines), we have observed such a fitness cost associated with virulent biotypes that can survive on aphid-resistant varieties (i.e Rag-containing soybeans).  We have a observed that Rag1+Rag2 pyramid provides season long protection from economic levels of soybean aphids without insecticides. However, this pyramid is not aphid-free; a virulent biotype is capable of surviving on the Rag1+Rag2 pyramid. The relationship between virulent, avirulent biotypes on aphid-resistant plants also suggest that a 'refuge-in-a-plant' is possible.  Virulent biotypes induce a systemic change in Rag-containing plants such that avirulent aphids survive on them, a phenomenon referred to as the obviation of resistance.  Finally, soybean aphids experience significant mortality from insect predators. In this presentation, we will discuss how a fitness cost, obviation of resistance and predation can be exploited within an insect resistance management plan for sustainable use of aphid-resistant soybeans.