Impact of switchgrass cultivar and cropping system on natural enemy communities and biological control services

Switchgrass (Panicum virgatum) is a perennial C4 grass that has potential for use as a dedicated bioenergy crop.  Switchgrass can produce high biomass yields while supporting other ecosystem services, including the biological control of pests.  This service is important because perennial cropping systems provide habitat for a variety of herbivores and their natural enemies.  To investigate the role of switchgrass cultivar and cropping system on natural enemy communities and biocontrol services, a network of plots of switchgrass, alone and in combination with other grasses and forbs, was established across southern Michigan.  In 2014 and 2015 the insect community of each plot was monitored in June-August via sweep net samples. Sentinel prey (Helicoverpa zea eggs) were used to measure the biological control service at corresponding times.  Levels of biological control increased over the season, and different cultivars and cropping systems supported varying levels of biological control.  Natural enemy communities also varied by cultivar, although biological control did not vary with community composition, which could be the result of functional redundancy between community members.  These results provide insight into insect communities and their provision of ecosystem services and will inform the choice of switchgrass cultivar and cropping practice in agricultural landscapes.