The effect of neonicotinoid pesticides on the circadian clock and sleep of fruit flies and bumblebees

  • Kiah Tasman

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Neonicotinoid insecticides are agonists of the nicotinic acetylcholine receptors that mediate excitatory, fast synaptic transmission throughout the insect nervous system. Due to their environmental prevalence and the involvement of the nicotinic acetyl choline receptors in many behaviours, neonicotinoids are a major factor in insect declines.

Many sub-lethal effects have previously been identified for neonicotinoids in beneficial insects. Here, the effects of four neonicotinoids, imidacloprid, clothianidin, thiamethoxam and thiacloprid, on the insect clock and sleep are characterised for the first time. Drosophila was used as a model, allowing rapid assessment of behavioural effects and investigation into the mechanism of action on the clock. Imidacloprid, clothianidin and thiamethoxam all disrupted locomotion and circadian rhythmicity and fragmented and reduced sleep in Drosophila. Thiacloprid only affected sleep.

Nicotinic acetylcholine receptor subunits Dα1, Dα3 and Dβ2 were then knocked down in the clock neurons. These knockdowns showed the same disruptions to circadian rhythmicity and sleep as seen in neonicotinoid exposed flies, suggesting these subunits are involved in sleep and circadian behaviour. Exposure of these flies to imidacloprid or clothianidin had no further effect on
rhythmicity, suggesting that neonicotinoids act upon the clock neurons to disrupt rhythmicity and that Dα1, Dα3 and Dβ2 mediate this effect. Exposure to imidacloprid or clothianidin or knockdown of Dα1, Dα3 and Dβ2 prevented the circadian remodelling of the dorsal terminals of the s-LNv clock neurons, further suggesting that neonicotinoids may act directly upon the clock neurons.

Behavioural assays were repeated in the buff tailed bumblebee Bombus terrestris. Foragers showed a reduction in locomotor and foraging rhythmicity. They also showed greatly reduced foraging activity and an increase in daytime sleep. Reduced foraging activity and rhythmicity is likely to reduce the capacity of colonies to grow and reproduce. This could be a contributary factor in insect
declines in the wild.
Date of Award12 May 2020
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJames J L Hodge (Supervisor) & Sean A Rands (Supervisor)

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