Bumble Bee and Honey Bee Density is Greater in Fields with a Diverse Seed Mix when Compared to Fields Planted to Timothy in Central Ohio, USA

Abstract

Pollinators are important for global food production and provide ecosystem services. However, many species of insect pollinators have declined in recent decades. Drivers of pollinator decline include habitat loss, invasive species, pesticides, and climate change. In Ohio, many species of pollinators (including butterflies, moths, and bumble bees) are considered species of greatest conservation need, while others have undergone population declines. This study evaluated butterfly species richness and diversity; butterfly, bumble bee, and honey bee density; and plant species composition of 2 planting regimes on state wildlife areas. Butterflies, bumble bees, and honey bees were recorded along 100 m transects within fields planted with timothy (Phleum pratense) and a diverse seed mix. Plant communities were assessed by measuring percent cover within quadrats placed every 10 m along the same transects. Mean plant species richness and diversity were significantly greater in fields planted in the diverse mix than in the timothy fields. As plant diversity increased, butterfly diversity increased. Density estimates of bumble bees (Bombus spp.) and honey bees (Apis spp.) were significantly greater in fields planted to the diverse mix than fields planted to timothy, with densities of bumble bees and honey bees being 536% and 529% greater, respectively, in the diverse mix fields than timothy fields. There were greater densities of butterflies in fields planted to the diverse mix than in the timothy fields; however, the differences were not statistically significant. Working to increase plant diversity in planted and restored grasslands benefits bumble bees, honey bees, butterflies, and likely other species of insects as well.