DEVELOPMENT & EVALUATION OF BIOLOGICAL CONTROL AGENTS FOR INVASIVE SPECIES THREATENING THE EVERGLADES & OTHER NATURAL AND MANANGED SYSTEMS
Location: Invasive Plant Research Laboratory
Title: Evolutionary interactions between the invasive tallow tree and herbivores: implications for biological control
Submitted to: Meeting Abstract
Publication Type: Proceedings
Publication Acceptance Date: July 14, 2009
Publication Date: October 1, 2010
Citation: Ding, J., Huang, W., Wheeler, G.S., Carrillo, J., Siemann, E. 2010. Evolutionary interactions between the invasive tallow tree and herbivores: implications for biological control. Meeting Abstract. Vol. 10, Article 166.
Interpretive Summary: Understanding mechanisms that contribute to biological invasions is crucial for managing invasive species. Different ideas have been proposed to explain invasion success of exotic plants. Among these, the enemy release hypothesis proposes that exotic plants are successful because of the absence of suppressive natural enemies from their native range. Additionally, when these exotic plants are released from natural enemies they evolve to become more competitive; they grow and reproduce more with reduced insect defenses. We examined two populations of the invasive weed, Chinese tallow and we compared the ability of plants from the native range (China) and the invasive range (North America) to resist and tolerate insect damage. Two insect species were used, one was a generalist that fed on many plant species; the other was a specialist and only fed on a few. The specialist grew more rapidly and ate more of the plants from the invasive population. This suggests that these invasive plants have reduced defenses compared with plants from the native range of Chinese tallow. Further these defenses are most effective against specialist insects. Also, these invasive plants had greater tolerance to insect damage as they grew more rapidly following damage. These results suggest that in the more than 200 years that Chinese tallow has grown in North America with little specialist insect damage, this invasive plant population has developed reduced resistance to specialist insects. Additionally, these invasive plants have developed greater tolerance to insects, especially toward the generalist species. These invasive plants with reduced resistance will be highly nutritious to specialist biological control agents however the plants’ tolerance to damage may reduce their control.
Understanding interactions between insect agents and host plants is critical for forecasting their impact before the insects are introduced, and for improving our knowledge of the mechanisms driving success or failure in biological weed control. As invasive plants may undergo rapid adaptive evolution during the process of range expansion, the potential evolutionary interactions of insect-plant may influence the effectiveness of biological control. In this presentation we will discuss the biogeographic variation in plant defense to insects in the tallow tree (Triadica sebifera) which is native to China but invasive in the US. Because the US populations showed reduced resistance but increased tolerance to herbivory by specialists, we predict that the invasive tallow tree may support a rapid population build-up of insect agents but the insects’ impact may be low if these specialists are introduced. Our chemical analysis shows that the US populations had low quantitative defense compounds but high qualitative defense compounds, which suggests that plants from invasive populations have altered chemistry that influences the development of insect biological control agents. We will also discuss our current study on the evolutionary interactions of above-below ground herbivores in tallow tree, which can affect invasion success, herbivore population dynamics and biological control. As invasive plants may employ novel defense strategies to cope with the differing herbivore communities, thus affecting biological control, we conclude that without taking into account the differences in resistance and tolerance to herbivores of plants from the native vs. invasive range, predictions of the ease of establishment of agents and their effectiveness at controlling host plants may both be incorrect.