PS 51-64
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 perennial grasslands decrease the abundance of natural enemies (predators and parasitoids) and biocontrol. Also, we asked whether landscape composition might offset any negative effects of harvesting. In 2013, we surveyed 18 grasslands in Wisconsin (9 were harvested in fall 2012; 9 were unharvested in fall 2012) for natural enemies using sticky cards, pitfall traps, and sweep-net sampling. We also measured biocontrol using egg card bioassays.
Results/Conclusions
Our results show that harvesting grasslands did not negatively influence natural enemy abundances. Rather biocontrol and some natural enemy groups (mostly ants) responded positively to harvesting which may be linked to greater grass biomass in harvested sites. Additionally, natural enemies were influenced by the landscape composition and for some predators (mostly aerial dispersers), landscape effects were stronger in harvested sites compared to unharvested sites. These results suggest that harvesting has no short-term negative effects for natural enemy abundances and biocontrol in grasslands but long-term implications are unknown. Sampling will continue in 2014 and include field sites in Michigan.