Does Predation Prevent or Promote the Evolution of Virulence in Soybean Aphids?
The soybean aphid (Aphis glycines) is the most economically damaging pest of soybean in the Northcentral US and can potentially cause substantial yield loss. Soybean aphids can be managed successfully with aphid-resistant soybean varieties. However, soybean aphids that can overcome plant resistance have been identified and these can threaten sustainable crop production. These aphids are virulent whereas aphids that cannot overcome plant resistance are avirulent. The refuge strategy (i.e. susceptible plants planted among resistant plants) can delay evolution of virulence by preserving a population of avirulent insects which dilute virulent aphid genetics. However, this refuge strategy alone is not capable of completely preventing evolution of virulence. We investigated the compatibility of combining the refuge strategy with aphid natural enemies. We hypothesized that natural enemies may further delay the evolution of virulence in soybean aphids. To test this, we infested susceptible and resistant plants with pure or mixed populations of virulent and avirulent soybean aphids for 10 days. Ladybeetle predators (Hippodamia convergens) were added to half of the plants and half were left without predators. After two days, aphid populations were counted on each plant and a random subset of aphids were removed from each plant for genetic analyses to distinguish virulent and avirulent aphids and calculate their relative frequencies. Preliminary results show that ladybeetles feed non-preferentially on virulent and avirulent aphids. These results suggest that natural enemies can be safely used with the refuge strategy to manage soybean aphids, as they do not contribute the spread of virulent soybean aphids.
Principal Investigator(s): Jessica Hohenstein