Defining species sensitivity and synergism potential for pesticides and pesticide mixtures through physiological traits analysis

Badder, Claire 2023. Defining species sensitivity and synergism potential for pesticides and pesticide mixtures through physiological traits analysis. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis investigates mechanisms and effects of chemical interactions on lepidopterans by analysing how toxicity is underpinned by toxicokinetic and toxicodynamic traits. Mamestra brassicae were exposed to a range of insecticides and fungicides representing several modes of actions, to identify synergistic or antagonistic effects. A novel high-throughput lepidopteran toxicity test was designed and trialled with a known toxicant, the organophosphate chlorpyrifos. This assay was suitable for assessing acute toxicity and toxicant effects on growth rates. To investigate chemical interactions, the effects of single compounds must be known. Using the novel bioassay, a range of five insecticides and four fungicides were screened for toxicity. Insecticides were toxic to larvae, except those targeting nicotinic acetylcholine receptors (nAChRs) such as imidacloprid and sulfoxaflor. Fungicide exposures caused no mortality. Of 13 binary mixture combinations tested, six showed a synergistic interaction, one an antagonistic and six no interaction (additive). The synergistic mixture of cypermethrin and prochloraz was taken forward for further testing. Sublethal and acute effects of this mixture were analysed in 2nd to 6th instar of M. brassicae larvae using the TKTD DEBTox model, highlighting synergistic effects on growth and survival. Finally, adult and larval sensitivity was compared to investigate effects of transcriptomic differences between the morphologically distinct life stages. Larvae and adults showed differential sensitivity to imidacloprid. A M. brassicae genome was sequenced and a larval and adult transcriptome generated to investigate this. Three detoxification enzyme families representing phase I, II and III metabolism were catalogued and transcriptomic differences analysed. Several of these enzymes were over 1000x upregulated in larvae, so represent potential drivers of this differential sensitivity. This work explores the mechanisms of synergistic chemical interactions via a multi-faceted approach including toxicity testing, TKTD modelling and metabolomics. This work will provide evidence to improve control of crop pests by implementing targeted pest management strategies based on life-stage sensitivities and also investigates the synergistic potential of pesticide mixtures, informing future pest management strategies and minimising risk of adverse effects to beneficial species.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Biosciences
Subjects:	Q Science > Q Science (General)
Date of First Compliant Deposit:	23 November 2023
Last Modified:	23 Nov 2023 16:54
URI:	https://orca.cardiff.ac.uk/id/eprint/164229

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