The prevalence, mechanism and evolution of agrochemical resistance in natural populations

Thesis

Agrochemical resistance is a growing problem endangering global food security. The cumulative increase in the number of resistant species since the introduction of the first synthetic pesticides in the 1940s and the projected increase of the global population place more stringent requirements on the yields of agricultural food production. An increased amount of damage is predicted to result from resistance to currently used agrochemicals due to the dearth of new chemicals being developed. Despite this, resistance biology lacks methods to study the phenomenon as a whole, beyond the identification of resistance conferring mutations in particular pest or lab populations.

This thesis tests the utility of using the model organism C. elegans to study the prevalence of naturally occurring resistance alleles, the dynamics of resistance emergence in controlled conditions, and the genetic basis of resistance from multiple sources. Assessing the presence of natural variation in chemical susceptibility utilising a genetically diverse panel of C. elegans indicated that resistance-conferring variation is widespread, as suggested by the identification of wild isolates naturally resistant to carbendazim and aldicarb. The observation of rapid adaptation to carbendazim exposure suggested a link between a high prevalence of natural resistance with fast emergence of resistance for benzimidazoles, while compounds of other modes of action, with high and low variation, saw no adaptation in experimental populations under the conditions tested. Identification of the genetic basis of carbendazim-resistance in strains of three different biological origins linked a C. elegans β-tubulin to the trait in all cases, indicating a high level of convergence and lack of stochasticity in the evolution of benzimidazole resistance. Furthermore, no fitness cost of benzimidazole resistance in the compound-free environment was identified under laboratory conditions, which is troubling as the presence of a fitness cost underlies many resistance management strategies.

Overall, the findings presented in this thesis provide evidence that C. elegans is a useful model system to study resistance biology in a holistic manner, particularly in an evolutionary context. An increased understanding of the natural prevalence, evolutionary biology and molecular basis of the phenomenon would better inform field strategies of resistance mitigation as well as computational models that study the interplay of complex parameters in emergence of resistance. Ultimately, this improved understanding could assist in minimising the danger of rapidly emerging resistant pest populations on global food security.

Authors: Parts, L

• DOI: 10.5287/ora-yj9x6bnea
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: Agriculture; Benzimidazole; Resistance; Wild isolates; Natural variation; Carbendazim; Pesticide; Evolution; Fungicide; Insecticide; Food security; Caenorhabditis elegans; Nematicide