Pollinators in biofuel agricultural systems: the diversity and performance of bees (Hymenoptera: Apoidea) on Jatropha curcas in Mexico

As with other biofuel crops, information on the effect of insect pollinators and landscape context on the productivity and sustainability of Jatropha curcas is lacking. We studied the effect of pollinator exclusion, self-pollination, cross-pollination and individual visits of the stingless bee Frieseomelitta nigra and the honey bee Apis mellifera on fruit set and weight of fruit and seed of J. curcas. We compared the relative abundance of both bee species on flowers and whether their attributes (ratio of male to female flowers, nectar quantity and quality) affect bee visitation rates. Finally, we sampled various plantations to analyze whether the proportion of forest surrounding a site affects bee abundance and diversity. Significant higher rates of fruit set were obtained from open, cross-pollinated, F. nigra and A. mellifera visited flowers compared to self-pollinated and non-pollinated ones revealing the importance of bees for fruit production. Frieseomelitta nigra and A. mellifera had a similar effect on fruit set and quality, but the former was significantly more abundant on the crop suggesting a better pollinator performance. Male flowers were significantly more visited than female ones by both bee species in spite of their similar amounts of nectar and sugar. The proportion of forest in the surrounding matrix had a positive correlation with bee diversity and abundance on plantations. Our results indicate that preserving patches of forest around the plantations may increase the presence of native bees on Jatropha flowers and ensure sustainable levels of pollination.