Promoting a new species of Cotesia as first biological control agent against the Mediterranean corn borer, an increasing pest. – CoteBio

WP1

Insect collection in the field and conservation in laboratory for experiments. Tests of parasitoid acceptance for oviposition. Choice test in ofactometer between target and non-target species.

WP2

Control of caterpillar parasitism allowing multiple parasitism of a single larvae or successive parasitism by one parasitoid of different larva.

Genetic studies: genome sequencing based on high throughput sequencing and genome assembly. Genetic mapping and QTL (Quantitative Trait Loci) mapping. Gene expression and quantification using quantitative PCR approaches.

Physiological studies: Ovary and testes dissection and estimation of gamete count with picture analysis tools.

WP3

Experiments performed in “insect proof” green house. Introduction of a controlled number of caterpillars of different stages using a randomized repartition in space. Introduction of a controlled number of parasitoids. Monitoring in laboratory of the exposed caterpillar to estimate the parasitism rate.

WP1
- localization and collect of 10 non-target species among 12 expected
- test of their attractiveness for the parasitoid
- implication of a digestive enzyme of the host larva in its acceptance by the parasitoid

WP2
2.1. Genomic components
- realization of a genetic map of C. typhae
- identification of 4 QTL involved in two traits, virulence and offspring number, and list of genes potentially involved
- sequencing, assembly and automatic annotation of C. typhae genome

2.2. Reproductive success components
- fertility: spermiogenesis dynamics and susceptibility to temperature variations; dynamics of ovocyte maturation
- realized fecundity: egg allocation along parasitism of successive host larvae

2.3. Reproduction and virulence
- quantity of virulence factors (viral particles) injected in the host larva by the parasitoid; lack of relationship with the expression of two virulence genes

WP3
First release of C. typhae on maize manually infested by S. nonagrioides larvae in insect-proof greenhouses. About 50% of host larvae have died from the parasitism, regardless of their developmental stadium, and with a slight effect of temperature, to be confirmed.

WP1
- test the susceptibility of non-target species, for those accepted by the parasitoid
- test dispersal capacities of the parasitoid
- test its ability to overwinter in France

WP2
2.1. Genomic components: many genes are localized on the QTL. Several approches (expression, resequencing, transcriptome analyses) will be realized to point out fewer genes at play in the studied phenotypes of virulence and offspring number
2.2. Fertility: susceptibility of ovocyte production to temperature variations
Fecundity: male mating capacity
2.3. reproduction and virulence
- differentiation between C. typhae strains: role of virulence gene expression in parasitized larvae ? Role of mutations oof these genes affecting protein efficiency. See methods in 2.1.

WP3: repetition of the first trial

WP4: will depend on the implication of a Kenyan company

BICHANG’A G.B., DA LAGE J-L, SAMBAI K., MULE S., LE RU B., KAISER L., JUMA G., MAINA E.N., CALATAYUD P.-A. 2018. Salivary a-amylase of stem borer hosts determines host recognition and acceptance for oviposition by Cotesia spp. (Hymenoptera, Braconidae). Frontiers in. Ecology & Evolution 6: 228. doi: 10.3389/fevo.2018.00228

CoteBio aims to conduct the research and development necessary for a future use of Cotesia typhae nov. sp. (Hymenoptera: Braconidae), a newly characterized insect parasitoid species, as a new biocontrol agent against the maize stem borer Sesamia nonagrioides (Lepidoptera: Noctuidae). Four converging facts signal the timeliness of this proposal: 1/ the discovery of this species of Cotesia which is strictly specific to S. nonagrioides in Africa, and which can develop on European populations of this host species; 2/ the expansion of S. nonagrioides populations in France due to milder winters, and the consequent losses in corn yield and quality; 3/ the difficulty to control the second generation of this pest, due to current regulation on insecticide use, prohibition of Bt corn and absence of efficient biocontrol agents; 4/ the increasing societal interest and need for healthier food.
So far, attempts to use a French endemic natural enemy against S. nonagrioides has failed because it could not be mass reared. C. typhae is a promising biocontrol agent because (i) efficiency and possibility of mass rearing have been assessed for one sister species, C. flavipes, which is widely used against the sugarcane borer in Brazil; (ii) we expect no environmental risk because C. typhae is host specific.
We have planned five work packages (WP) to achieve the goal of CoteBio.
WP1 will evaluate risks and benefits of introducing C. typhae in France, in the frame of a regulatory process relative to the introduction of exotic macro-organisms for plant protection. Based on the biology and ecology of C. typhae and sister species, we will evaluate the risk for non-target species, and on C. typhae possibility to overwinter and establish.
WP2 aims at identifying mechanisms of C. typhae reproductive success and the factors of variation, by uncovering physiological and behavioral components of this success, the genes involved and their function. Results will improve the understanding of insect reproduction, and will allow identifying the most promising C. typhae strain for large scale production and biocontrol.
WP3 will test the parasitic efficiency of C. typhae against S. nonagrioides on maize plantations in greenhouses, based on the experience gained with C. flavipes, and using different parasitoid strains, temperature ranges and host stages.
WP4 will set up methods for host and parasitoid mass rearing with the perspective of industrial production and commercialization. Different temperatures, diets, and semi-automated rearing systems will be tested in a perspective of sustainable costs, and possibilities of parasitoid storage.
WP5 will be devoted to the scientific coordination and juridical aspects of the project.
The consortium gathers 2 public research labs working in the field of insect ecology, evolution and physiology: EGCE & IRBI, and 2 private partners: the company Bioline which has a unique R&D department involved in the biocontrol of crop pests, and the technical institute Arvalis in charge of improving corn protection and production and informing farmers. The partners have elaborated the WPs together and will develop them in collaboration.
The project is the first step towards the use of C. typhae for maize bio-protection against the Mediterranean borer. It is based on a wide knowledge of the ecology, population genetic, behavior and physiology of species of the C. flavipes complex. It will produce the report required for the authorization of C. typhae introduction in the environment. Progress that will be made in the production and release methods of the parasitoid may lead to a patent shared between the partners. If successful, the biocontrol agent against S. nonagrioides will allow reducing chemical treatment of maize. This project will also contribute to understand behavioral and molecular processes at play in reproductive success and adaptation to new habitats, which are essential components of successful biological control programs.