Harvesting and landscape effects on natural enemy abundance & biocontrol in perennial grasslands

Perennial grasslands generally support a higher abundance and diversity of beneficial insects compared to conventional biofuel crops such as corn, at both the local and landscape scales. However, harvesting grasslands for biofuel production might have negative consequences for beneficial insects by serving as ecological "sinks". In this study we asked whether harvesting grasslands decreased the abundance of natural enemies, NEs (predators and parasitoids) and biocontrol. Also, we asked whether landscape composition might offset any negative effects of harvesting. In 2013 and 2014, we surveyed 18 grasslands in Wisconsin USA (nine were harvested in fall 2012 and 2013; nine were not harvested in fall 2012 and 2013) for NEs using sticky cards, pitfall traps, and sweep-nets. We measured biocontrol using egg card bioassays. Our results from 2013 show that harvesting grasslands did not negatively influence the total abundance of NEs. Rather biocontrol and some NE groups (mostly ants) responded positively to harvesting which may be linked to greater grass biomass in harvested sites. Additionally, NEs were influenced by the landscape composition and for some NE groups, landscape effects were stronger in harvested sites compared to non-harvested sites. These results suggest that harvesting has no short-term negative effects for NE abundances and biocontrol in grasslands but long-term implications are unknown.