The effects of neonicotinoids and increasing temperatures on the thermoregulation and flight ability of South African honey bees, Apis mellifera scutellata (Lepeletier)

Abstract

Predicted climatic changes throughout the southern African region are likely to affect the distribution of ecological zones, significantly impact agricultural yield, and influence the timing of the flowering season. Climate change has the potential to influence pollinators, especially the honey bee; reducing survival, affecting behaviour and physiology, as well as impacting biodiversity and agriculture. Similarly, agriculturally significant neonicotinoid pesticides have been found to negatively impact many aspects of honey bee physiology and survival. Their widespread usage in Africa and the effects on its pollinators therefore necessitates further investigation. The physiological and behavioural thermoregulatory activities of Apis mellifera scutellata, and how they are affected by exposure to three neonicotinoid active ingredients (clothianidin, imidacloprid and thiamethoxam), was investigated. On an individual level, a baseline thermotolerance for A.m. scutellata was established (LT50=53.77 °C). Exposure to sublethal neonicotinoid doses elicited a 3 °C drop in the LT50 of A.m. scutellata. Flight efficiency and associated parameters were assessed under three different ambient temperatures, both with and without sublethal neonicotinoid exposure. Using flight parameters as a proxy for flight muscle function and by extension thermoregulatory ability, it was found that the majority of parameters were not significantly impacted in A.m. scutellate. However, the honey bees’ ability to initiate flight at all was severely affected. Colony level thermoregulatory efficiency was measured using a custom built, in-hive monitoring system that recorded internal hive temperatures at five second intervals over three months. This monitoring was performed both before and after sublethal neonicotinoid exposure. Following neonicotinoid exposure, it was observed that the hives exhibited considerable resilience in terms of maintaining the closely regulated temperatures in the brood frame area. However, the outlying areas within the hive showed more unpredictable fluctuation. These three studies demonstrate that 1) individual LT50 dropped by 3 °C, 2) flight initiation was impaired and 3) colony level thermoregulation efficiency was reduced in non-brood areas, when exposed to sub-lethal neonicotinoid active ingredients clothianidin, imidacloprid and thiamethoxam. More importantly, these results highlight the importance of how the effects may be further exacerbated in the context of both local and global climatic change. These changes include the increased frequency and intensity of extreme weather events. The unique agricultural landscape of South Africa encompasses commercial, small scale and subsistence farming practices that employ varied uses of insecticides, which further contribute to these effects. The results of the studies demonstrate the importance of further research into the effect of these insecticides on honey bees in the unique agricultural context.