Use of Native Bumblebees (Bombus atratus Franklin and Bombus bellicosus Smith) to Improve Seed Production of Red Clover (Trifolium pratense)

Abstract

In Uruguay the historical production of red clover seeds (Trifolium pratense) is slightly over 100 kg/ha. This low value can be explained by the difficulty of pollination in this species. The aim of this study was to assess the red clover seed yield under field conditions using native bumblebees Bombus atratus and Bombus bellicosus as main pollinators. In this work, we used a red clover field of 250 x 200 m planted with cultivar Estanzuela 116 in its second bloom. In February 2010, seven colonies of ombus atratus and three of Bombus bellicosus (mean ± SD: 99 ± 36 individuals) were located along one side of the field. Twenty five experimental plots of 5 x 2 m were established at different distances from the nests. In April, red clover seed from each plot was harvested and seed yield indicators were calculated. The average proportion of seeds per flower of the inflorescence was 64.4 %, higher than the maximum reported in Uruguay (62 %), but no correlation was found between this indicator and the presence of bumblebees. However, it was found that the number of bumblebees was associated with the number of mature inflorescence/m², the number of inflorescences/m² and seed yield (g/m²). These results show the feasibility of obtaining good yield of red clover seeds in Uruguay using the native bumblebees.