Effects of Neonicotinoid Exposure on Anti-predator Behaviour and Learned Recognition of Novel Predator Odour of Larvae Lestes spp. (Odonata: Zygoptera)

Abstract

Neonicotinoids are widely used water-soluble neurotoxic insecticides. The effects of these insecticides on non-target aquatic organisms have become a major environmental concern since they affect both pests and non-target insects. Along with lethal effects, these insecticides could cause visual and chemoreception impairment. This can lead to behavioural alterations in aquatic organisms by disrupting the sensory systems used for detecting predators, thereby affecting antipredator behaviours. Therefore, in this thesis, I investigated the effect of imidacloprid, a neonicotinoid insecticide, on the anti-predator response and learned recognition of novel predator odour in damselfly larvae (Lestes sp). In the first experiment (chapter 2), damselfly larvae were exposed to water contaminated with a series of concentrations (0.0μg/L, 0.1μg/L, 1.0μg/L, and 10.0μg/L) of imidacloprid and the change in number of feeding bites performed after injecting a conspecific damage-released alarm cue solution and a predator kairomone solution was observed and recorded on day 2, 5, and 10. On days 2 and 5, both the control and 0.1μg/L groups showed appropriate anti-predator behaviour to alarm cues and predator odour, but this was not the case for damselflies exposed to 1.0μg/L. By day 10, larvae in the 1.0 and 10.0μg/L groups no longer responded to alarm cues and all exposure groups ceased responding to predator odour. In the second experiment (chapter 3), I investigated the effect of exposure to a series of concentrations of imidacloprid on learned recognition of predatory stimuli by damselfly larvae. Damselflies were conditioned to recognize risk by exposing them to zebrafish odour (a novel odour) combined with conspecific damage-released alarm cues or control of dechlorinated water. Larvae in the control group learned to respond to the predator odour based on their prior conditioning with alarm cues but not water. Learning of predator odour also occurred for larvae in the 0.1μg/L treatment group but failed for individuals exposed to the higher concentrations of 1.0μg/Land 10.0μg/L. In the third experiment (chapter 4), I exposed damselfly larvae to imidacloprid (at an initial pulse solution of 3.0μg/L and reaching a final concentration of 0.01μg/L) during the conditioning period and evaluated the effect on learned recognition of novel predatory stimuli. Damselflies were conditioned to recognize risk by exposing them to zebrafish odour with true conditioning (alarm cue + predator odour) with or without imidacloprid and another group was given sham conditioning (water + predator odour) with or without imidacloprid exposure. Larvae given true conditioning without imidacloprid exposure correctly learned to recognize theiii predator odour as a threat, while larvae given sham conditioning, and those exposed to imidacloprid, failed to learn to respond to the predator odour. Overall, this study highlights that acute and chronic exposure to imidacloprid at both environmental relevant and higher concentrations impairs the anti-predator response to conspecific alarm cues and predator odour by damselfly larvae. Further, this study demonstrates that imidacloprid affects learned recognition of novel predator odour by damselfly larvae with the interaction between chemical cues and imidacloprid potentially playing a key role in this impairment.