Climate change and species invasions will likely be two of the most important environmental disturbances of the 21^st century.  We must therefore understand the dynamics of invasive species in the context of global warming.   Moreover, because ecological interactions may shape species’ responses to these disturbances, consideration of the effects of these disturbances on communities rather than individual species is ideal.  This study considers how warming affects a plant-herbivore-natural enemy system, utilizing soybean Glycine max, the soybean aphid Aphis glycines, and Asian lady beetle Harmonia axyridis.  Since the first records of naturalized A. glycines and H. axyridis in North America in 2000 and 1988 respectively, both have become invasive.  Previous studies have shown elevated temperatures reduce G. max performance and have a non-linear effect on A. glycines population growth rates, first increasing then decreasing growth.  Our study considered the direct effects of increased temperature on G. max and A. glycines and considered whether temperature affected H. axyridis’ regulation of A. glycines.   In 2009, we built four ambient and four elevated (ambient +3^oC) 3m diameter open air rings in Southwest Michigan and planted G. max within each ring.  We studied both natural colonization and manipulated densities of A. glycines and H. axyridis.

Results/Conclusions

In contrast to previous studies, we found that elevated temperature improved G. max performance.  Specifically, elevated temperature increased the rate of ontogeny (p<0.0001), ultimate aboveground biomass (p=0.006), and ultimate height (p=0.016) but reduced the root to shoot ratio of G. max (p=0.0012).   When natural colonization of A. glycines and H. axyridis were allowed, elevated temperature increased A. glycines population growth (p<0.0001).  Caged manipulation studies also showed elevated temperature increased A. glycines population growth both in the presence and absence of H. axyridis (p<0.0001).  These results suggest that climate change may act to increase population growth rates and the invasive potential of A. glycines in North America.  However a numeric response of H. axyridis to increased densities of A. glycines could mitigate the effect of temperature on aphid populations.  Furthermore, 2009 was a notably cool summer.  Because of the non-linear response of A. glycines population growth to temperature, the effect of elevated temperature on A. glycines population growth and this system in general may differ in warmer summers or in latitudes further south.