Adaptation in Biological Control - Parasitoid Population Genomics – ABC - PaPoGen

In two Hymenoptera parasites of plant pest caterpillars, Hyposoter didymator and Cotesia sesamiae, natural or experimental populations, issued from natural selection, crossings or experimental selection will be genotyped using recently developed high throughput sequencing techniques. Statistical tools will be adapted for allowing the characterization of quantitative genetic statistics of adaptation and determining which markers vary with individual fitness i.e. are linked to quantitative trait loci (QTL) of adaptation. Specific tools developed in this project will allow testing adaptation in the field and evaluating its expected positive agricultural or potentially negative ecological consequences. The sequencing of Cotesia and Hyposoter genomes, will make it possible to localize the QTL in the genome, and annotation will link these QTL to candidate genes contributing to the adaptation to host and habitat in parasitoid Hymenoptera.

The molecular analysis of populations of the parasitic wasps Cotesia sesamiae in Cameroon has been done before and after inoculative release of Kenyan strains of the wasp, selectioned for their efficiency against the maize pest Busseola fusca. Results show that C. sesamiae samples collected in wild habitats (forest) are all endemic to Cameroon. The biocontrol operation has thus preserved forest endemic races of the wasp.
A high quality genome of Cotesia congregata is now available as reference genome for the project.

following of the project

Drezen et al. Origin and evolution of endogenous viruses associated with parasitoid wasps. Current Opinion in Insect Science

Climate change and wild habitat destruction induce dynamic and genetic changes in insect pest populations menacing agriculture (shifts in distribution range, adaptations, and apparitions of pest traits). Against pest invasions, natural enemies are selective and non-polluting control agents that should preserve biodiversity. Being introduced for acclimatization in new environment, biological control agents also constitute model systems for the study of adaptation to environmental changes. ABC-PaPoGen will characterize adaptive mechanisms of biological control agents against agricultural pests, both in the laboratory and in the field. The aims are to study behavioural and physiological adaptive traits to host and habitat, in order to establish new highly virulent strains useful for bio-control applications and safe for the environment. We will consider adaptations at different time scales: in the long term between locally adapted host populations and in the short term against new hosts by experimental selection or new environment in the context acclimatization following biological control operations. The samples, characterized for fitness traits on the host, will be genotyped using Next Generation Sequencing methods. Newly developed statistical and bioinformatic tools will be used to identify genes linked to adaptation.
Two hymenoptera parasitoid species will be studied; Cotesia sesamiae, an African Braconidae, parasitoid of noctuid stemborers of Poacae and other monocotyledons and Hyposoter didymator, a Palearctic Ichneumonidae parasitoid of folivorous noctuids of cultivated plant. The two insects are associated with immune suppressive polydnaviruses symbionts and differ in their reproductive strategy (gregarious or solitarious) and genome organization (clustered or dispersed integration of virus genome in the parasitoid genome). We predict that these differences will lead to different adaptive diversification strategies. The project is based on important published knowledge in behaviour, population genetics and ecological specialization in C. sesamiae, in virulence genomics in the genus Cotesia, and in the area of proteomics and genomics for H. didymator.
We plan to characterize (i) long term adaptive genetic differentiation in relation to local host through the analyses of mendelian crosses between populations of both C. sesamiae and H. didymator for behavioural, developmental and physiological traits; (ii) short term adaptation genetics to new hosts through experimental selection of a C. sesamiae strain with high parasitism on Sesamia nonagrioides infesting maize in France; and (iii) short term adaptation to new host and habitats through natural selection survey of C. sesamiae strains introduced in Cameroon against Busseola fusca a Lepidopterous stemborer of maize and sorghum and recovered after a few years of acclimatization. These different samples originating from crosses, experimental selection and natural selection will be genotyped using recently developed high throughput sequencing techniques (RAD sequencing). Statistical tools will be adapted for allowing the characterization of quantitative genetic statistics of adaptation and determining which markers vary with individual fitness i.e. are linked to quantitative trait loci (QTL) of adaptation. Specific tools developed in this project will allow testing adaptation in the field and evaluating its expected positive agricultural or potentially negative ecological consequences. The sequencing and assembly of whole Cotesia genome and of the Hyposoter genome, partly included in this project, will make it possible to localize the QTL in the genome, and annotation will link these QTL to candidate genes contributing to the adaptation to host and habitat in parasitoid Hymenoptera.