Dissemination of phosphorescent microbial agents by honey bees (Apis mellifera L.) in apple orchards

Honey bees are commonly used for pollination in apple orchards. This study aimed to develop a bee-vectoring scheme whereby honey bees (Apis mellifera L.) deliver microbial agents (Bacillus amyloliquefaciens MBI600) against fire blight from a dispenser at the entrance of the beehive to apple flowers. The efficiency of disseminating phosphorescent microbial agents (PMA) by honey bees was compared across four apple orchards; (A) with installed insect nets, (B) isolated on an island, (C) adjacent to other apple orchards and apiaries, and (D) near C within 50 m and without beehives. The average detection ratio of PMA on bees visiting flowers was 100 % in orchard (A) and (B), whereas in (C) and (D) it was 54.5 % and 40.0 %, respectively. Detection of PMA on apple blossoms was also 100 % in (A) and (B), but significantly low in (C) and (D) at 52.8 % and 12.9 %. In orchards (A) and (B), PMA adhered to pistils at high ratios of 98.0 % and 96.3 %, while in orchard (C), it was significantly lower at 9.3 %. Phosphorescence intensity in flowers and the proportion of apple pollen loads collected from incoming bees were also investigated. Finally compared to the orchard (A) and (B), open orchard (C) and (D) showed significantly lower microbial agent spread efficiency by honey bee vectoring. For open orchards, supplemental strategy to enhance bee vectoring could include increasing the number of hives in the orchard and temporarily relocating neighbor’s beehives during flowering, or supplying additional dispensers to nearby apiaries.