Application of Optical Fluorescence Spectroscopy for Studying Bee Abundance in Tropaeolum majus L. (Tropaeolaceae)

SIMPLE SUMMARY: Tropaeolum majus L. is a medicinal plant popularly known as capuchinha. It produces flowers of different colors and hence attracts various groups of floral visitors. Since these groups may be potential pollinators, they are major for biodiversity conservation. In this regard, our study aimed to verify potential relationships between corolla colors and visiting bee abundance using optical fluorescence spectroscopy and climatic analyses. Orange and yellow flowers were the most visited and showed higher temperatures and fluorescence emissions than did flowers of other colors. This might be due to the presence of compounds such as hydroxycinnamic acid and kaempferol that emit fluorescence around 470 to 620 nm, which are within the visible spectrum for these bee species. ABSTRACT: Tropaeolum majus L. species produce flowers with all sorts of colors, from yellow to red. This work aimed to apply optical fluorescence spectroscopy to study bee abundance in T. majus, answering the following questions: (1) do corolla temperature and weather conditions affect the abundance of visiting bee species? (2) do flower color and corolla fluorescence affect the abundance of visiting bee species? (3) do red flowers attract more visiting bees? (4) is there a relationship between bee visits and flower compounds? The bee species Apis mellifera, Paratrigona lineata, and Trigona spinipes were the most observed in T. majus flowers. The latter was more active in the morning and preferred orange and yellow flowers. These colors also had higher temperatures and fluorescence emissions than did the red ones and those with yellow-red and orange-red nectar guides. Orange flowers emitted a broadband UV spectrum (between 475 and 800 nm). This range might be due to compounds such as hydroxycinnamic acid, flavonols, isoflavonoids, flavones, phenolic acid, and chlorophyll. Extracts from different T. majus corolla colors showed that flowers emit specific fluorescent signals, mainly related to bee color vision and learning, thus acting as a means of communication between bees and flowers. In this way, this information evidences the interaction between bees and T. majus flowers, allowing conservation actions for pollinators.