Action: Reduce tillage
Evidence on whether reduced tillage or no tillage benefits ground-nesting bees is mixed. Two replicated trials on squash Cucurbita spp. farms in the USA had contrasting results. One showed no difference in the abundance of bees between tilled and untilled farms, the other found three times more squash bees Peponapis pruinosa on no-till farms than on conventional farms.
Supporting evidence from individual studies
Two replicated trials have compared the effects of tillage on the abundance of squash bee and other bees visiting squash Cucurbita spp. flowers in the United States. Both studies used 20 or more farms, in the same area (Virginia or Maryland, USA). Shuler et al. (2005) found that there were three times more squash bees on no-till farms as on tilled farms, although there was no difference in the numbers of bumblebees Bombus spp. or honey bees Apis mellifera. By contrast, Julier & Roulston (2009) found no difference in the numbers of squash bees or other bees between farms that had tilled after the previous year's pumpkin crop and those that had not. Julier & Roulston's study only included farms growing pumpkins, which are relatively late flowering compared to other cultivated squash plants. Early emerging squash bees may have been missed by this study because they had to travel elsewhere to forage and nest.
Julier H.E. & Roulston T.H. (2009). Wild bee abundance and pollination service in cultivated pumpkins: farm management, nesting behaviour and landscape effects. Journal of Economic Entomology, 102, 563â€573