Wildflower plantings in commercial agroecosystems: The effects on pollinators, predators, herbivores, and floral communities

Abstract

Beneficial insect populations and the services they provide are in decline, largely due to agricultural land use and practices. Establishing perennial floral plantings in the unused margins of crop fields can help conserve beneficial pollinators and predators. Floral plantings also have the potential to promote biological control services in commercial agroecosystems. To assess how floral plantings impact pollinator conservation and biological control of crop pests, we studied floral plantings established adjacent to conventionally managed commercial potato fields. We measured 1) Floral communities in field margins, 2) Pollinators and arthropod predators, 3) Biological control of the main pest of potatoes in the region, Colorado potato beetle (CPB), and 4) Detrimental arthropod herbivores. 1. Field margins with floral plantings led to significantly increased floral cover and richness compared to unmanaged field margins. This effect was consistent across the majority of the growing season. Floral margins also had a greater proportion of perennial and native flowers. 2. To determine how floral plantings impacted the conservation of beneficial insects, we sampled pollinators and arthropod predators both in the margins of potato fields and within potato crops themselves. Floral plantings significantly increased the abundance of pollinators within floral margins compared to unmanaged margins, and the effect increased with increasing floral cover within margins. The overall abundance of arthropod predators was also increased in floral plantings, although it was unrelated to floral cover. Within adjacent potato crops, the presence of floral plantings in field margins had no effect on the abundance of pollinators or predators. 3. Colorado potato beetle egg masses were placed within field margins and at the edge of potato crops to directly assess predation rates. While floral plantings increased the abundance of CPB predators, they did not significantly increase the rate of predation of sentinel CPB egg masses within field margins. Within nearby potato crops, predator abundance and predation rates on CPB eggs were unaffected by the presence of flowers. However, orthopteran abundance was positively associated with predation of CPB eggs, and orthopterans were observed consuming sentinel CPB eggs. Orthopterans could prove to be an unexamined predator of CPB. Colorado potato beetle numbers in potato crops were not impacted by floral plantings. Preliminary data from our study indicate floral margins may provide improved overwintering opportunities for CPB, and further investigation is needed. 4. Floral plantings did not result in a greater abundance of herbivores within field margins or within nearby potato fields. Floral plantings did alter the community composition of herbivores, with floral margins attracting more orthopterans, and control margins attracting more herbivorous hemipterans. Our results show floral plantings increase the abundance of beneficial insects in field margins, but do not increase abundance in nearby crops. Biological control of CPB was unaffected. Floral plantings improved floral communities, and did not promote herbivores or CPB in potato crops, although further study on their potential as overwintering sites for CPB is needed. Establishing floral plantings on a large scale in commercial agroecosystems can help conserve both pollinators and predators, but may not increase ecosystem services.