Brassica plants promote Apis mellifera visitation to Japanese apricot in cold conditions

Abstract

Floral resource enhancements are widely used to boost insect pollination in various crops. The Japanese apricot, a winter-flowering fruit crop, requires mid-winter pollination. However, cold weather can restrict pollinator activity. In this study, we explored the use of Brassica plants, which bloom fully during the Japanese apricot blossom period, as additional flower resources to promote honey bee visitation. We sowed Brassica rapa and used existing feral Brassica plants as additional floral resources to compare the honey bee visitation frequency, visitation behavior, and the number of pollen grains on the stigmas of Japanese apricot flowers with those of the control group. The visitation of the managed honey bee (Apis mellifera) to the Japanese apricot flowers was studied at temperatures below 15 ºC. Under such cold conditions, Brassica flowers increased A. mellifera visitation in both the experimental and commercial orchards. Brassica-rich orchards exhibited clear positive effects of flower resources. Observations of flower-visiting behavior and pollen grains on the stigmas suggest that the increased honey bee visitation to Japanese apricot flowers was not caused by spillover from the Brassica flowers. The flower resources did not increase the number of pollen grains on the Japanese apricot stigmas irrespective of the increase in the number of honey bee visits. Fruit production instability caused by cold weather is a major issue in the agricultural management of commercially cultivated Japanese apricot. The findings suggest that Brassica plants can solve pollination-related problems in Japanese apricot orchards. In addition, Brassica plants are easy to grow, do not have common pests with Japanese apricot, and are beneficial for both apiarists and farmers. Therefore, Brassica plants are a promising floral resource for use in Japanese apricot orchards.