Background

The development of resistance in pests is a classic example of evolution in action and a major problem in agronomy. In the case of resistance to living microorganisms such as viruses used as biological control agents, understanding the adaptive mechanisms involved can help manipulate the "arms race" between the virus and its host and solve the agronomic problem posed by the resistance. Codling moth (Cydia pomonella) is the major pest of apple and pear orchards worldwide. A biological control method is used to control this lepidopteran: the granulovirus: Cydia pomonella GranuloVirus (CpGV). Each granulovirus being specific to one or a few species of insects and harmless to all other living beings, the use of these viruses is in line with the objectives of reducing the use of chemical insecticides and preserving the environment. The CpGV is one of the few effective methods available to Organic Agriculture in apple and pear orchards. After more than 20 years of large-scale use of a single viral isolate (CpGV-M), virus-resistant populations of C. pomonella have been detected, raising the question of the sustainability of this biological control method. Three previous theses have developed a new variant, CpGV-R5 capable of bypassing C. pomonella resistance to the virus in the laboratory and in the field, and studied genotypic mixtures to sustain the efficacy of this biological control (Berling, 2009; Graillot, 2015; Hinsberger, 2020). It is the component of the product Carpovirusine Evo2, commercialized by UPL A third variant also effective on resistant insects was commercialized at the same time under the name CpGV-V15 by the company Andermatt Biocontrol. In 2020, our team detected several populations with decreased susceptibility to the three isolates currently marketed in France (Siegwart et al. 2020).

Objectives

Our research group has started a new collaboration with UPL to investigate the genetic mechanisms of coevolution between the virus and its host. The aim of this PhD project is i) to elucidate the genetic basis of new resistances in C. pomonella; ii) to develop molecular tools for high throughput detection of these resistances and iii) to develop durable efficient viral isolates. These three objectives will involve experimental evolution (host-virus coevolution), adaptive genomics and virology approaches.

(C. pomonella grannulovirus)

Photo credit : Isabelle Bornard (INRAE)