Effects of Neonicotinoid Exposure on Anti-predator Behaviour and Learned Recognition of Novel Predator Odour of Larvae Lestes spp. (Odonata: Zygoptera)
Date
2023-01-24
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
Type
Thesis
Degree Level
Masters
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.
Description
Keywords
Neonicotinoid, antipredator
Citation
Degree
Master of Science (M.Sc.)
Department
Biology
Program
Biology