Do flower-tripping bees enhance yields in peanut varieties grown in north Queensland?

Abstract

It has been demonstrated that tripping of peanut flowers by large bees enhances pollination and improves peanut yields of some early commercial peanut varieties but this phenomenon has not been evaluated for recently developed peanut varieties. Our study aimed to establish whether bees provide this service for peanut varieties currently grown on the Atherton Tableland, north Queensland. To measure the impact of native and introduced bees occurring without assistance in crops, we set up 3 cage treatments (meshed to exclude large bees; partly meshed to allow bee access but take cage effects into account; and unmeshed) in each of 7 peanut crops. We also trapped bees in each crop for the entire flowering period. In a separate experiment, designed to ensure that suitable large bees were abundant nearby, we set up 6 replicates of the same 3 cage treatments in another peanut crop where 4 honeybee colonies were located. On a sunny day, during peak flowering, we monitored the number of honeybee visits to the peanut flowers in this crop between 0820 and 1730 hours. At harvest, we found that there was no effect of treatment on peanut yield (number of peanuts/g plant biomass). Thus, bees were not contributing to peanut pollination. This was reflected in the fact that no honeybees (or native bees) were observed visiting peanut flowers in the crop augmented with honeybees, and even though we caught 6 species of suitably sized bees in the other peanut crops, no bee species was common. It seems likely that selection for other desirable peanut traits has resulted in development of varieties that are no longer attractive to flower-tripping bees and that there is no advantage to be gained by north Queensland growers promoting bees in crops of these varieties.