Abstract
The honey bee (Apis mellifera) is an important pollinator and also an important test model for pesticide effects on other insect pollinators. Honey bees have been experiencing high mortality in both the US and worldwide and pesticide exposure has been identified to be one of the many stressors causing this mortality. Effects of various pesticides have been measured for multiple responses such as learning, memory performance, feeding activity, and thermoregulation. These studies were conducted at many different temperatures (11- 35°C), however, almost no studies compared toxicity of the same pesticide to bees at different temperatures. It is possible that the same pesticide might show different toxicity to honey bees at different temperatures. To reveal such potential interactions, we administered low doses of two neonicotinoid insecticides (imidacloprid and thiamethoxam) at different temperatures (35, 24 and a varying temperature) and determined their effects on honey bee survivorship. We discovered that honey bees are much more sensitive to neonicotinoid pesticides, imidacloprid and thiamethoxam, at a constant 24oC or at a varying temperature (night at 13oC and day at 24oC) compared to bees at 35°C. These results suggest that honey bee colonies during winter time will be more sensitive to pesticides. Doses of neonicotinoids that are safe to colonies during summer might kill them during the winter time.
Highlights
Pollinators are responsible for the transfer of pollen between flowers, helping fruit and seed production in approximately 88% of flowering plants (Ollerton et al, 2011)
There was a significant negative effect of both neonicotinoid insecticides on the survival of caged honey bees compared to the control when kept at 24◦C (Log Rank Test; X2 = 63.5, df = 2, P < 0.001, Figure 1A, Trial 1)
When the survival data were analyzed over the 4 days, there was a significant negative effect of both neonicotinoid insecticides on the survival of caged honey bees at 23◦C; the survival of bees between the two pesticides was significantly different, with imidacloprid having a greater negative effect on survival (Log Rank Test; X2 = 24.3, df = 2, P < 0.001, Figure 1C)
Summary
Pollinators are responsible for the transfer of pollen between flowers, helping fruit and seed production in approximately 88% of flowering plants (Ollerton et al, 2011). Whereas a wide variety of animal taxa can work as pollinators (Ollerton, 2017), honey bees (Apis mellifera) are highly efficient in pollen transfer and are used for the majority of pollination services in both cultivated and wild plants (Willmer et al, 2017). Great attention has been paid to the effects of neonicotinoid pesticides on honey bees and their potential role in harming the health of honey bee colonies all over the world (Matsumoto, 2013). These systemic insecticides are strong agonists of the nicotinic acetylcholine receptors (nAChR), mainly circulated in the insect. The sublethal effects of neonicotinoids on honey bees have been extensively studied at many different physiological levels (Aliouane et al, 2009; Henry et al, 2012; Catae et al, 2014; Oliveira et al, 2014; Alburaki et al, 2015), but whether this toxicity interacts with low temperature has not yet been explored
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