Visitation of Apis mellifera L. in Runner Bean (Phaseolus coccineus L.) and Its Exposure to Seasonal Agrochemicals in Agroecosystems

Abstract

Plant species and abiotic factors including season appear to be the most important variables influencing the frequency of visits by honeybees (Apis mellifera L.). In the present study, we evaluated the activity of honeybee workers visiting runner bean (Phaseolus coccineus L.) local cultivar ‘Piękny Jaś’. The runner beans are widely cultivated in south-eastern Poland, and are an important forage plant for honeybees in agroecosystems. We aimed at a comprehensive monitoring of the health of colonies and symptoms in A. mellifera in response to acute exposure to pesticides. The most numerous visits of A. mellifera were observed at the highest flower opening of the runner bean. A very weak positive correlation was observed between the number of honeybees on P. coccineus, the number of visited flowers, the time spent per flower and air temperature. The visitation rates of honeybees were more frequent at mid-day and decreased after 15:00. Signs of poisoning were detected in two out of seven apiaries monitored for acute pesticide exposure symptoms on runner bean plantations. The analysis of dead honeybee samples revealed the acute exposure of honeybees to the imidacloprid (neonicotinoid) and chlorpyrifos (organophosphorus) insecticides, which are highly toxic and banned in the European Union. Hazard quotient (HQ) screening showed an elevated burden of imidacloprid and chlorpyrifos corresponding to 7.1% and 10% of the LDD50, respectively, most likely indicating bee poisoning due to chronic exposure to these substances with contaminated food. Noteworthy was the presence of three fungicides that could pose a risk of poisoning in honeybees.