A fundamental challenge for biocontrol practitioners is to select agents that will have a large negative effect on the ecological success of their host plant. Factors that may influence the ability of a specialist herbivore to control an invasive plant are: relative availability of limiting resources to plants, herbivore mode of feeding, and allocation patterns of the invader and native plants. We used resource competition models to predict how each of these factors will likely impact the effectiveness of control agents. 
Results/Conclusions

Limiting resources and mode of feeding - First, in models of single species (monocultures), we found that below-ground herbivores have a large impact on host plants in soil resource limited ecosystems and above-ground herbivores have a large impact in light limited ecosystems. In the reverse situations, such as root herbivory in light limited ecosystems, herbivores have little effect.  Limiting resources and plant traits - Next, we examined models of competition between invasive and native plants. Regardless of their mode of feeding (below-ground vs. above-ground), biocontrol agents were more likely to control their host plants when they fed on either (1) invaders that were superior light competitors in ecosystems with high availability of light relative to soil resources or (2) superior soil resource competitors in ecosystems with low availability of light relative to soil resources.  Combinations of factors - But, biocontrol agents were most likely to control their host plants for the combination of either (1) above-ground feeding herbivores, an invader that was a superior competitor for light, and high availability of light relative to soil resources or (2) below-ground feeding herbivores, an invader that was a superior competitor for soil resources, and low availability of light relative to soil resources. Conclusions - We explored these scenarios in the context of Chinese tallow tree invasions into coastal prairies in the southern United States. Our results suggest that above-ground herbivores will be the most effective control agents in prairies (especially low productivity ones). In general, we suggest that linking traditional community ecology more closely with the study of invasions and biocontrol may bring new insights to each field.