Can near-infrared exposure help mitigate pesticide-impaired thermoregulation in adult bees?

Abstract

For terrestrial animals, maintaining body temperature is vital for successful movement, feeding and reproduction. Exposure to environmental toxins such as pesticides, however, may place individual thermoregulation at risk. Identifying potential mitigative solutions is thus important, especially given widespread pesticide applications across landscapes are forecast to continue. In mammals, near infrared (NIR) light has been put forward as a method for countering the effects of toxin exposure, but limited evidence has been found for insects. Here, we orally expose an important insect pollinator group - adult bumblebees - to a cholinergic pesticide (a neonicotinoid) to first quantify the baseline impact on body temperature (using thermal imaging), and second to investigate how exposure to near infrared (NIR) light mediates this effect. For bumblebees kept at 18{degrees}C ambient we show, relative to control bees who maintained their body temperature at ca.30{degrees}C, that neonicotinoid exposed bees exhibited a steep (by nearly 8{degrees}C) body temperature drop over the 73hr assay showing a pattern of convergence towards ambient. We did however find some evidence that NIR can partially counter such neonicotinoid impairment. Of two different wavelengths (600nm, 850nm) and three exposure durations (5, 10 or 20 minutes per hour), we found evidence that 660 nm for 5 minutes appeared to more than halve the rate to which the neonicotinoid decreased body temperature. Yet, intriguingly, the mitigation effect of 660 nm NIR appeared to lessen as exposure time increased. We further found tentative evidence that 850 nm for 20 mins may alleviate the decline in body temperature (by nearly 40%). In conclusion, our study further highlights a mechanism by which pesticides threaten the critical functioning of non-target organisms but also provides a potential therapy worthy of further investigation.