Implications of Three Biofuel Crops for Beneficial Arthropods in Agricultural Landscapes

Abstract

Production of biofuel feedstocks in agricultural landscapes will result in land use changes that may have major implications for arthropod-mediated ecosystem services such as pollination and pest suppression. By comparing the abundance and diversity of insect pollinators and generalist natural enemies in three model biofuel crops: corn, switchgrass, and mixed prairie, we tested the hypothesis that biofuel crops comprised of more diverse plant communities would support increased levels of beneficial insects. These three biofuel crops contained a diverse bee community comprised of 75 species. Overall, bees were three to four times more abundant in switchgrass and prairie than in corn, with members of the sweat bee (Halictidae) and small carpenter bee (Ceratina spp.) groups the most abundant. Switchgrass and prairie had significantly greater bee species richness than corn during the July sampling period. The natural enemy community at these sites was dominated by lady beetles (Coccinellidae), long-legged flies (Dolichopodidae), and hover flies (Syrphidae) which varied in their response to crop type. Coccinellids were generally most abundant in prairie and switchgrass, with the exception of the pollen feeding Coleomegilla maculata that was most abundant in corn. Several rare or declining coccinellid species were detected in prairie and switchgrass sites. Dolichopodidae were more abundant in prairie and switchgrass while Syrphidae showed no significant response to crop type. Our results indicate that beneficial insects generally responded positively to the increased vegetational diversity of prairie and switchgrass sites; however, when managed as a dedicated biofuel crop, plant and arthropod diversity in switchgrass may decrease. Our findings support the hypothesis that vegetationally diverse biofuel crops support higher abundance and diversity of beneficial insects. Future policy regarding the production of biofuel feedstocks should consider the ecosystem services that different biofuel crops may support in agricultural landscapes.

Agroenergy Crops Influence the Diversity, Biomass, and Guild Structure of Terrestrial Arthropod Communities

“…Herbivorous arthropods will act as pests of biomass crops, capable of reducing the quantity or quality of biomass harvested [17]. Conversely, other arthropod groups such as decomposers, pollinators, predators, and parasitoids will enhance nutrient mineralization and plant performance in biomass crops [18,19], enhance pollination services [20], and assist in the control of herbivorous crop pests [17,21], respectively. Insomuch as expansion of biomass production can shape arthropod communities and influence arthropod biodiversity, selection of biomass crops can change the ways arthropod-mediated ecosystem services such as pollination and pest suppression are distributed in agricultural landscapes [14,17].…”

“…Alternative biomass feedstocks may differ profoundly in their ability to support native biodiversity and provision ecosystem services [3,20,[23][24][25]. In regard to terrestrial arthropod populations, low-input, high-diversity mixedgrass prairie reconstructions (sensu [26]) and switchgrass monocultures (Panicum virgatum) have recently been found to support a greater diversity and abundance of bees and a higher abundance of two important predator groups (Coccinellids and Dolichopodids) than corn [20].…”

“…In regard to terrestrial arthropod populations, low-input, high-diversity mixedgrass prairie reconstructions (sensu [26]) and switchgrass monocultures (Panicum virgatum) have recently been found to support a greater diversity and abundance of bees and a higher abundance of two important predator groups (Coccinellids and Dolichopodids) than corn [20]. Here, we take a community-wide perspective and build on previous work by examining the diversity, richness, and feeding guild structure of terrestrial arthropod communities in crops ranging from an intensively managed, annual monoculture to diverse plantings of perennial grasslands.…”

Is bioenergy for the birds? An evaluation of alternative future bioenergy landscapes

“…The consequences of increased demand for land associated with bioenergy crops initially gained attention because of the implications for carbon emissions associated with land clearing (2,3), but, more recently, the potential impacts of bioenergy's land demand on biodiversity have gained increased attention (4)(5)(6). The study by Meehan et al (7) in PNAS provides a quantitative look at predicted landscapescale biodiversity impacts under alternative bioenergy cropping scenarios.…”

“…Expansion of corn for ethanol is expected to exacerbate issues associated with nutrient pollution (10), air quality (11), greenhouse gas emissions from land use change (3), and habitat for biodiversity (4)(5)(6) in contrast to cellulosic ethanol, which offers the potential for environmental benefits in these areas (2,6,8,11,12).…”