Perennial bioenergy plantings enhance an ecosystem service and provide resources for beneficial insects in agricultural fields

Background/Question/Methods

Diversified, perennial crops show promise to improve the efficiency and sustainability of bioenergy and biomaterial production. Plant biodiversity in agricultural landscapes can increase the abundance and diversity of beneficial arthropods, leading to enhanced ecosystem services, such as pollination and biological control of pests. The soybean aphid, Aphis glycines, is a serious invasive pest that has caused a 130-fold increase in insecticide use on US soybean acreage. This study examines the efficiency of integrated cropping systems (soybean with short-rotation willow and prairie polyculture) to produce bioenergy and support natural enemies and biological control of the soybean aphid.

The abundance of soybean aphids and their natural enemies (e.g., lady beetles, lacewings, minute pirate bugs, hoverflies, parasitoids, etc.) within perennial crops and in adjacent soybean was measured throughout the growing season using a combination of sampling methods. Biological control was quantified by monitoring soybean plants with experimentally elevated soybean aphid densities (‘flared aphids’) at each plot for two weeks. Additionally, bioassays were performed on the gut-contents of field-collected natural enemies to determine the extent of perennial crop-provided resource utilization: polymerase chain reaction (PCR) for alternative prey, anthrone for floral and extra-floral nectar, and acetolysis for pollen.

Results/Conclusions

Soybean fields immediately adjacent to willow plots showed an increased abundance of several natural enemy groups, including minute pirate bugs (Orius insidiosus), lacewings (Chrysopidae and Hemerobiidae) and damsel bugs (Nabis spp.). Soybean adjacent to prairies had higher abundance of lady beetles (Coccinellidae). However, no significant differences in predator populations were found at further distances (15 m) from perennial crops. Willows supported a greater abundance of lacewing adults and eggs than all soybean control plots. Aphid populations (final density-initial density/initial density) were significantly reduced on soybean plants adjacent to willow, prairie or alley crops (combined willow and prairie) after being exposed to natural enemies in the field for two weeks compared to plants adjacent to all-soybean control plots. Pending PCR, anthrone and acetolysis results will reveal levels of trophic connectivity between natural enemies and resources provided by bioenergy crops, potentially providing the mechanisms for observed increases in abundance and biological control. These data support the proposal that diversified, perennial bioenergy crops can promote populations of beneficial arthropods and enhance ecosystem services when integrated within monoculture crops. This system has the added potential to decrease insecticide usage by providing biological control of an agricultural pest.