Collaborative Research: Stability of eco-evo dynamics and the maintenance of biodiversity in a host-parasitoid system

This project investigates how the rapid evolution of an agricultural pest makes it more difficult to control using natural means. People think of evolution occurring in geological time, with eras like the Dinosaur Age populated with different organisms from what we have on Earth today. Most studies of evolution, however, look at changes that occur in days or years in organisms that are all around us today.

Scientists are realizing that rapid evolution is common and affects all organisms. For example, many agricultural pests in the USA are controlled by predators that attack and kill them, making insecticides unnecessary. Pea aphids represent a great example of this, because they are kept in check by predators.

However, pea aphids can evolve resistance to predators. This rapid evolution raises the risk of greater crop damage. Despite their ability to evolve resistance, all the pea aphids do not become resistance to predators.

There are also some that remain susceptible, creating a balance between resistance and susceptibility. This project aims to uncover how this balance is maintained, and how agricultural management practices can reduce the risks of agricultural pests becoming resistant. Understanding this balance will help to develop strategies to make US agriculture more resilient and increase the security and sustainability of our bioeconomy.

The project will also provide hands-on research experiences to students with no prior experience. Public outreach events will engage farmers to share the results of the research broadly.

The research investigates the ecological-evolutionary dynamics of pea aphids and their parasitoid wasp, Aphidius ervi. Aphidius ervi was deliberately introduced to North America as a biocontrol agent of pea aphids, particularly to control pea aphids as pests of alfalfa crops. Pea aphids are a leading model for investigating the evolutionary and ecological consequences of symbiosis because all populations harbor heritable symbionts that provide well-documented benefits.

The most common and best studied facultative symbiont, Hamiltonella defensa, confers resistance against A. ervi. Although evolutionary theory predicts that resistance traits will often be bimodal (either susceptible or highly resistant), pea aphids exhibit a full spectrum of resistance through different symbiont variants. Although the prevalences of different symbiont variants fluctuate (reflecting the intensity of parasitism and selection), the collective of symbionts across the spectrum of resistance appears to be stable.

Furthermore, the ecological interactions between pea aphids and A. ervi are stable, in the sense that A. ervi is always present but abundances never get high enough to extirpate pea aphids. This ecological stability of A. ervi-pea aphid interactions may itself be the product of the evolutionary stability of the symbionts that confer pea aphid resistance to A. ervi.

The research will use field experiments, lab experiments and mathematical modeling to examine both the evolutionary and ecological stability of A. ervi-pea aphid interactions, and whether this stability is generated by the interconnections between evolutionary and ecological dynamics.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.