Pesticide contamination and their botanical sources in pollen loads collected by honeybees in Kenya: A spatio-temporal context

Honeybees are generalists, and therefore, a wide range of flowering plants can easily be identified from their collected pollen loads. In this study, the levels of pesticide contamination on corbicular pollen were investigated using two approaches; (i) unsorted colony level collected and (ii) sorted pollen samples (according to botanical origin). Sorted samples were palynologically identified up to the family level to establish the types of pesticides used across landscapes and identify their botanical sources. This study was carried out between November 2019 and October 2020 in Murang’a county, Kenya, across three landscape types. The landscape was characterized according to the degree of greenness using the Normalized Difference Vegetation Index (NDVI) into high, medium, and low classes. Pollen Hazard Quotient (PHQ) was used to estimate the risk to honeybees of each detected pesticide. In the unsorted samples, five different pesticides were detected with concentrations ranging between 0.12 and 37.97 µg kg-1. From the results, 11 pesticides were detected, nine insecticides and two fungicides. These pesticides were further traced to 11 plant families, from which Poaceae, Rubiceae, and Astereceae were contaminated with more than 70% of the 11 detected pesticides. Acetamiprid concentration in March was found to be extremely higher (1202.50 µg kg-1) the recommended EU limit (50 µg kg-1). Additionally, chlorpyriphos concentration was found to be higher than the EU set limit of 10 µg kg-1 in months of July, September, and October. Additionally, pollen from Rubiaceae and Poaceae plant families were the most collected during the period of this study. It was further noted that pesticides and plant families identified varied across sampling time, but not across landscapes.