Predicting the Next High-Impact Insect Invasion

Science Center Objects

Although most introduced insects are relatively benign, some become high-impact pests causing widespread ecological and economic damage. Introduced insects that are specialists and feed on a single genus of plants can be high-impact as they can potentially eliminate an entire native plant genus over large areas. Luckily, most introduced insects with this feeding behavior do not become high-impact pests. However, there is great need to predict, prior to their introduction, which insects have the potential to result in high-impact invasions so risk assessment and management are informed. 

A group of USGS, Forest Service, and university scientists are working together to study how ecology and evolution might be used to understand when introduced insects become high-impact. We are examining the contribution of five types of drivers toward these impacts: (1) the insects’ and host plants’ evolutionary history, (2) the hosts’ defenses or lack thereof (defense-free space), (3) presence of natural enemies or lack thereof (enemy release), (4) invader traits, and (5) geographic and temporal considerations.

 

 

conceptual diagram of the drivers that may determine the impact of a specialist insect pest
A conceptual diagram of the drivers that may determine the impact of a specialist insect pest. We posit that the relationship between evolutionarily naïve host plants and invasive insect species is the strongest driver of a high-impact invasion. The diagram, modified from the synthetic invasion meta-framework described by Gurevitch et al. (2011), is guiding our USGS Powell working group’s data compilation and synthesis. Click on image to enlarge it.

Background & Importance

Within their native range, where the insects and their host plants evolved together (coevolution), host plants develop effective defenses that limit insect feeding.  Plants are often less resistant to introduced insects when a coevolutionary history with the insects is lacking; they are considered to be evolutionarily naïve. Many examples of invasions in North America that have caused wide-spread death of native plants, are introduced insects that specialize on feeding on a particular genus of plants that are evolutionarily naïve to that insect. In order words the plant lacks defenses to the insects feeding on them.

Introduced insects also may have the benefit of release from their natural enemies that are present in their native environment. Release of natural enemies is often provided as a reason for the ability of the introduced insect to persist and spread. However, release from natural enemies provides only a partial explanation for invasion success. A far less-studied mechanism is the defense-free space hypothesis that states it is insufficient defenses of the host plants that allow the invading insect to thrive. Researchers have demonstrated the importance of including the lack of coevolved defenses in establishing the risk of invasion, they have not sufficiently incorporated the role of coevolved plant defenses into explanations of impacts of invasion.

General Methods

The USGS Powell Center sponsors researchers to meet and work together on a problem. Our working group has been addressing this problem through telephone conferences in late 2015 and 2016 and our first in person work meeting in Fort Collins in July 2016. We plan to continue our work throughout 2017 and 2018 and have planned our second week long in person work meeting in August of 2017.

We are focusing on introduced insects in North America that feed on native plants. The project has three implementation components data compilation and synthesis, model development and validation, and model evaluation and application. The conceptual diagram of drivers of invasive insect impact (see image)  will guide our initial selection of introduced species and their representative traits and factors. These traits and factors will serve as predictor variables incorporated into and tested in a statistical model predicting invasion impact. Lastly, we will apply the parameterized model to insects not yet established in the U.S. to develop a probability ranking of those insects likely to become significant threats if introduced.

References Cited

Gurevitch, J., Fox, G.A., Wardle, G.M., Inderjit, and Taub. D., 2011, Emergent insights from the synthesis of conceptual frameworks for biological invasions: Ecology Letters, v.,14, p. 407-418.