Using bumblebees (bombus terrestris) as bioagent vectors to control sclerotinia head rot on sunflower in Serbia

Abstract

The ability of commercial bumblebees to transfer Clonostachys rosea spores as a biocontrol agent (BVT-CR7 strain) from the hive to sunflower heads for the control of Sclerotinia head rot was studied during 2016 and 2017 in field trials. The bumblebee hives were placed in isolation cages before flowering and allowed to adapt to the new environment. The bumblebee activity in 2016 was significantly lower in the confined space compared with colonies in the open field, while in 2017 their activity was similar at all sites. Artificial inoculation with Sclerotinia sclerotiorum ascospores was done at full bloom, and end of flowering. Floret samples collected at the end of the flowering period confirmed the presence of C. rosea in treated plants (7.4%). The presence of S. sclerotiorum was lower (up to 30%) than in the control heads, confirming efficacy of the treatment. Statistical tests showed that the difference in disease incidence was highly significant between successive evaluations. Mean disease incidence was 2, 13 and 57% when the biocontrol agent was present compared to 6, 26 and 68% in the controls. Seed samples showed that seed yield, 1000 seed weight, hectoliter mass and seed germination were increased in the treated plants for 11, 1, 3 and 6%, respectively. These results indicate that bumblebees can be used as efficient vectors of C. rosea spores to sunflowers for the suppression of Sclerotinia head rot and the added benefits of insect-mediated pollination.