A common neonicotinoid pesticide, thiamethoxam, alters honey bee activity, motor functions, and movement to light

S Tosi,J C Nieh

doi:10.1038/s41598-017-15308-6

Abstract

Honey bees provide key ecosystem services. To pollinate and to sustain the colony, workers must walk, climb, and use phototaxis as they move inside and outside the nest. Phototaxis, orientation to light, is linked to sucrose responsiveness and the transition of work from inside to outside the nest, and is also a key component of division of labour. However, the sublethal effects of pesticides on locomotion and movement to light are relatively poorly understood. Thiamethoxam (TMX) is a common neonicotinoid pesticide that bees can consume in nectar and pollen. We used a vertical arena illuminated from the top to test the effects of acute and chronic sublethal exposures to TMX. Acute consumption (1.34 ng/bee) impaired locomotion, caused hyperactivity (velocity: +109%; time moving: +44%) shortly after exposure (30 min), and impaired motor functions (falls: +83%; time top: −43%; time bottom: +93%; abnormal behaviours: +138%; inability to ascend: +280%) over a longer period (60 min). A 2-day chronic exposure (field-relevant daily intakes of 1.42–3.48 ng/bee/day) impaired bee ability to ascend. TMX increased movement to light after acute and chronic exposure. Thus, TMX could reduce colony health by harming worker locomotion and, potentially, alter division of labour if bees move outside or remain outdoors.

Highlights

Pollinators provide essential ecosystem services, and the honey bee, Apis mellifera L., 1758, is a major global pollinator of crops and native plants[1]
Thiamethoxam (TMX) is one of the most widely used neonicotinoids because TMX and its degradation products are highly toxic to insects[9,14]
Amines, serotonin[23], octopamine, and tyramine[24] modulate phototaxis. Because these biogenic amines modulate a variety of other behaviours and physiological states[23], phototaxis can be an indicator of bee sensitivity to other stimuli, such as nectar sugar concentration

Summary

Introduction

Pollinators provide essential ecosystem services, and the honey bee, Apis mellifera L., 1758, is a major global pollinator of crops and native plants[1]. Neonicotinoid pesticides are of particular concern because they are neurotoxic insecticides that are used globally on multiple crops visited by honey bees to collect food resources[7,8,9]. Ben-Shahar[21] showed that a honey bee foraging gene (amfor) encodes a cGMP-dependent protein kinase that controls bee positive phototaxis Upregulation of this gene is associated with the age-related transition from in-hive to outside-hive tasks (i.e. foraging)[21]. Foragers walk and climb on combs and recruit by dancing[28], which necessitates coordinated locomotion[29] Outside the nest, they can walk upon inflorescences to obtain nectar and pollen and must use coordinated leg motions to collect pollen and resin[20]. Our understanding of the effects of neonicotinoids such as TMX on bee locomotion and movement to light remain relatively limited

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Conclusion