Abstract
Thirty-two honeybee (Apis mellifera) colonies were studied in order to detect and measure potential in vivo effects of neonicotinoid pesticides used in cornfields (Zea mays spp) on honeybee health. Honeybee colonies were randomly split on four different agricultural cornfield areas located near Quebec City, Canada. Two locations contained cornfields treated with a seed-coated systemic neonicotinoid insecticide while the two others were organic cornfields used as control treatments. Hives were extensively monitored for their performance and health traits over a period of two years. Honeybee viruses (brood queen cell virus BQCV, deformed wing virus DWV, and Israeli acute paralysis virus IAPV) and the brain specific expression of a biomarker of host physiological stress, the Acetylcholinesterase gene AChE, were investigated using RT-qPCR. Liquid chromatography-mass spectrometry (LC-MS) was performed to detect pesticide residues in adult bees, honey, pollen, and corn flowers collected from the studied hives in each location. In addition, general hive conditions were assessed by monitoring colony weight and brood development. Neonicotinoids were only identified in corn flowers at low concentrations. However, honeybee colonies located in neonicotinoid treated cornfields expressed significantly higher pathogen infection than those located in untreated cornfields. AChE levels showed elevated levels among honeybees that collected corn pollen from treated fields. Positive correlations were recorded between pathogens and the treated locations. Our data suggests that neonicotinoids indirectly weaken honeybee health by inducing physiological stress and increasing pathogen loads.
Highlights
Honeybee populations around the world have declined significantly in the last decade [1, 2]
Several studies highlight the impact of endemic and emergent pathogens [3,4,5,6,7]; others blame the excessive use of pesticides [1, 8]
Multiple chemical residues of synthetic origin have been detected inside honeybee hives, including pesticides used in varroa treatment [9, 10]
Summary
Honeybee populations around the world have declined significantly in the last decade [1, 2]. The phenomenon of global honeybee decline represents a major challenge for beekeepers and scientists alike. Several studies highlight the impact of endemic and emergent pathogens [3,4,5,6,7]; others blame the excessive use of pesticides [1, 8]. Multiple chemical residues of synthetic origin have been detected inside honeybee hives, including pesticides used in varroa treatment [9, 10]. No individual factor such as environment, pesticide or pathogen, seems to act as the principal driver of Colony Collapse Disorder (CCD) or other honeybee losses. The massive decline of honeybee populations in the world is widely considered a multifactorial phenomenon [11]
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