Effects and associations of the production of the biofuel crop Brassica napus on wild invertebrate pollinator communities in the South Central United State

The addition of biofuel crops to the agricultural landscape is drastically changing habitats around the world with unknown environmental consequences. Agricultural conversion of land negatively affects pollinators which are in decline globally, but semi-natural lands such as pasture can have positive effects on pollinator communities. Pollinators provide free ecological services and increase crop production of entomophylous plants. The biofuel crop canola (Brassica napus) provides floral resources that may benefit pollinators, and has higher yield when pollinated. Conversely, insect pests can substantially reduce canola production, so 90% of canola fields are treated with insecticides, many of which can be harmful to pollinators. In the South Central US, canola is generally planted in rotation with winter wheat, and has increased from 0 to 109,265 hectares since 2007. We tested whether pollinator abundance, richness, and diversity within and around canola fields were different in areas with and without pasture during and after canola bloom. Bees were captured (2011-2014) during April (peak canola bloom), (2012-2014) June (post-harvest when no more flowers were available) and (2012-2014) August (several months after canola had been harvested), using blue vane traps for 48 hours each period. Butterflies were captured using yellow sticky traps (2011-2013) during peak canola bloom at the same locations. Additionally, trap nests for twig nesting bees were used in 2013 and 2014 to evaluate reproductive success of bees during canola bloom. Fruits of a wild entomophylous plant were collected to investigate reproductive success of wild plants after canola was harvested. Our data show adjacent pasture did not significantly increase bee or butterfly diversity, richness or abundance around canola fields but bumble bees were only present at sites with pasture. Reproductive success of bees did not significantly differ between sites with and without adjacent pasture; however, parasitism rates were highest in areas without pastures. Plant reproductive success was significantly higher in areas where canola was produced than in areas where it was not produced and bees were more abundant in June, after canola was harvested. Landscape analysis showed correlations of land cover with pollinator abundance and richness, which varied between morphospecies and time of the year.