A Fluorescência e a temperatura da corola de Tropaeolum majus L. (Tropaeolaceae) interferem na abundância de abelhas

Abstract

Some plant species have the ability to produce flowers of different shades, from yellow to red, as is the case of Tropaeolum majus. This diversity of flower colors stems from the presence of secondary metabolites that absorb UV rays and emit the colors of the petals. Thus, the bees have adapted their vision to changes in UV emission, and with this they are able to identify the flowers at long distances. Therefore, few works have addressed the relationship between the color of the corolla and the floral visitors, so the present work aimed to verify if there is a relationship between the different colors of the corolla of T. majus and the abundance of visiting bees, using optical fluorescence spectroscopy and climate analysis. In the experimental area, we observed the bees that visited T. majus flowers, as well as the temperature and color of the visited flowers and the weather conditions of the day in the period of seven weeks. A total of 1,035 bees of the species Apis mellifera, Paratrigona lineata and Trigona spinipes were found in the transects of T. majus, the latter being more active in the visitations. When observing the color of the corolla, the yellow and orange flowers received more visitors, especially from A. mellifera and T. spinipes. Among the times preferred by bees, T. spinipes preferred the three different times (9:00 am to 10:00 am; 12:00 pm to 1:00 pm and from 2:00 pm to 3:00 pm differing significantly from the others, however, A. melliferera preferred the morning time (9:00 am to 10:00 am) for make your visits. For the correlation tests, we observed that the abundance of visiting bee species and the average temperature of the corolla of different colors was considered positive and significant between T. spinipes and orange flowers, A. mellifera and flowers orange-red and red and between P. lineata and red flowers, where the abundance of bees increased when the temperature of the flower corolla increased. For the correlation of the abundance of visiting bee species with climatic conditions (temperature, relative humidity and wind speed) at different times of the day, we observed a positive and significant correlation only between T. spinipes and the temperature from 9:00 am to 10:00 am, however , from 12:00 pm to 1:00 pm T. spinipes had a positive and significant correlation with all weather conditions of the day, while for the time from 2:00 pm to 3:00 pm, only P. lineata had a positive and significant correlation with the temperature of the day. For fluorescence tests, flower extracts were measured in two different experimental settings. The first consisted of obtaining better resolutions of fluorescence spectra and understanding the plant mechanisms involved in them. The second aimed to simulate the exposure of T. majus flowers to sunlight. As a result, the orange and yellow flowers showed higher temperatures and fluorescence emissions than the red ones and those with nectar guides, yellow-red and orange-red. The orange flowers emitted a broadband UV spectrum (between 475 and 800 nm). This range may be due to compounds such as hydroxycinnamic acid, flavonols, isoflavonoids, flavones, phenolic acid, and chlorophyll. Extracts of different corolla colors showed that flowers emit specific fluorescent signals, mainly related to vision and color learning by bees, thus acting as a means of communication between bees and flowers. Therefore, it is concluded that the corolla color characteristics interfere with the abundance of visiting bee species, as well as there is a relationship between the visits of the bees with the floral compounds present in the different colors of the flowers, with the kaempferol compound being the most abundant. in orange flowers, responsible for the highest emission of fluorescence of these flowers, and consequently, being the floral, most visited by the species of bees present in the transects of T. majus.