Evaluating the impact of winter cover crops on predator abundance & biocontrol services in continuous corn biofuel cropping systems

Corn stover will soon be harvested for cellulosic ethanol. To prevent losses of soil organic carbon, winter cover crops may be integrated into continuous corn systems. Cover crops “green up” early in the spring, at a time when few other resources are available to natural enemies (especially in landscapes dominated by annual crops). These cover crops are known to support aphids that could provide important resources for natural enemies emerging from overwintering. These aphid resources could increase early season populations of natural enemies within the cover crop. Additionally, natural enemies sheltering in the cover crop stubble may spillover into the corn crop, enhancing the predator community compared to conventionally grown corn. Alternatively, such cover crops could serve as a “sink” if natural enemies invest offspring in the habitat which are subsequently disturbed (by harvest and/or herbicide application) prior to their reaching maturity and dispersing. In the spring and summer of 2013 and 2014 we monitored aphids and their predators in four biofuel crops (continuous corn, corn with covercrop, switchgrass and prairie) in Michigan and Wisconsin. During 2013 we did not see a strong effect of cover-cropping on biological control services, but we did see differences between the four crop types and a general increase in biological activity as the summer progressed. Ants and spiders were found in high numbers during 2013. This year we are using night vision capable video cameras in Michigan to determine if ants and spiders are responsible for removing sentinel prey in the crops. Unlike last year, we have detected populations of aphids in the MI cover crop treatment that may attract natural enemies and effect biological control in the subsequent corn crop.