The influence of nectar sugar production on insect visitors to flowers of Brassica rapa L.

Abstract

The purpose of this study was to determine if differing amounts of floral nectar sugar could affect the insect pollination of Brassica rapa L., a self-incompatible species. This knowledge could be directly applicable to crop-breeding programs interested in maintaining or enhancing the attractiveness of flowers to nectar-foraging visitors (possible pollinators). Several lines of rapid-cycling B. rapa were assayed (microcapillary nectar collection plus refractometry) for floral nectar-sugar production, and seed increases were made from plants selected on that basis. Both high and low nectar-producing plants were crossed reciprocally (high by high and low by low) in attempts to establish progenies distinct from each other. It appeared that reliably high and low nectar-yielding lines could be established. Outdoor insect visitation trials using high, intermediate, and low nectar-yielding lines of rapid-cycling plants of B. rapa in small plots resulted in more insects (especially flies and bees) visiting the high nectar-producing line, which in turn produced more seeds per silique.