Biointeraction and Biosecurity Lab

1 Biological invasions and pest management under global changes

We have been working on how globalization and climate change affect invasive species and agricultural pests, such as aphids in wheat. We quantitively assessed how China's booming economy sparked and accelerated biological invasions in China (BioScience 2008). We found many factors were contributing to the developing problems, including an increase in the number of ports of entry, the number of travelers, and the amount of imported goods as well as the expanding network of express highways and more domestic air travel.

With the globally invasive alligator weed and a specialist beetle, our study highlights the importance of shifting interactions of invasive plants and insects driven by climate-warming to plant invasions (Global Change Biology, 2013). The invasive plant and their feeding insects have different responses to warming, resulting in either "enemy release" or "enemy increase" that have contrasting effects on plant invasions.

2 Co-evolved interactions of invasive plants, herbivores and AMF fungi

We have been particularly interested in the evolution of invasive plants and their antagonists (herbivores) and mutualists (AMF fungi). We examined resistance and tolerance of Chinese tallow tree populations from the introduced and native ranges to generalists and specialist herbivores in the native range. We found differences in selective pressures between ranges have caused dramatic reductions in resistance to specialist herbivores but increased tolerance to generalists (Journal of Ecology, 2010). Our further studies showed changes in plant secondary chemistry likely underlie these differences (Journal of Ecology, 2012). Our study also indicated that invasive tallow populations may adopt an ''aboveground first'' strategy in which the invader allocates resources aboveground, which not only increases tallow's competitive ability for resources but also enhances its ability to tolerate aboveground herbivory (Ecology, 2012).

Currently we are investigating the potential role of AMF fungi played in increasing tolerance in the introduced populations and whether the enhanced mutualisms are regulated by plant chemical signals that have evolved in plant invasions.

3 Above and belowground interactions in natural and agricultural settings

With the tallow and its specialist Bikasha flea beetle as a model system, we found aboveground conspecific adults facilitated belowground larvae, but belowground larvae inhibited aboveground conspecific and these contrasting interactive effects may be mediated by changes in plant nitrogen and secondary chemicals (Proceedings of the Royal Society B, 2013). Further study reveals that while conspecific aboveground adults facilitate belowground larvae, other aboveground insect damage inhibits larvae or has no effect. Belowground larvae increase conspecificcadult feeding, but decrease heterospecific aboveground insect feeding and abundance. Thus, specific plant herbivore responses allow herbivore facilitation and inhibition to co-occur, likely shaping diverse aboveground and belowground communities (Nature Communications, 2014).

We are now testing whether herbivory-induced plant volatiles function as signals to link these above and belowground herbivores, and what are the implications for agricultural pest insect management.

4 Biological control of invasive plants: agent selection, efficacy and non-target effects

Biocontrol has been evolving from experience-based toward to science-based theory and technology. In the last decades the developing multidisciplinary theories, techniques and many case studies on invasion ecology and ecology of insects and plants allow us to better assess and predict biocontrol efficacy, non-target effects and tackle the climate change challenges. We have been working closely with colleagues around the world (Australia, USA, Europe and South Africa) for screening potential biocontrol agents for invasive plants and assessing their host specificity and efficacy.

Many introduced insects establish populations on their target invasive plant; however, their impact is not sufficient to curb the invasion. Our results from tests on the effects of specialists on introduced and native populations of tallow found reduced resistance and increased tolerance to herbivory by the specialists in introduced populations may impede success of biological control, suggesting including plants from the introduced range in the prerelease evaluation will help predict insect impact on target weeds (Ecological Applications, 2011).

Given climate change can shift interactions of invasive plants, herbivorous insects and native species, studies of risks to non-target species from biocontrol agents under climate change are critical for future management of invasive species and conservation of native species. With field surveys and warming experiments on alligator weed, its native congener and the specialist beetle, we found warming can shift phenologies, increase non-target effect magnitude and increase non-target effect occurrence by beetle range expansion to additional areas where the non-target congener occurs (Ecology letters, 2015). Further study indicates the biocontrol insect could mediate warming effects on competition between the invasive and native hosts, indirectly shaping plant communities (New Phytologist, 2016).