Several initiatives were launched in Europe to regulate the use of chemical inputs. Among these, France has adopted the Ecophyto 2018 plan, which aims at reducing pesticide use. In this context, the development of effective biological control programs against pests has been pointed out as an important need. The genus Trichogramma (Hymenoptera) is one of the most studied and commercialized groups to control pests of major economic importance in Europe. As Trichogramma are among the smallest insects (ca 1mm) and morphological characters to define species are often unreliable, the systematics of the group is unclear and Trichogramma are frequently released without taxonomic, genetic, phenotypic or behaviour characterization and in-depth risk assessment study. For example, many Trichogramma species are described as highly polyphagous and habitat-generalists, which has been presented as a potential drawback for their use in biocontrol against specific target. However, so called “generalists” could instead be complexes of specialist species each being specific of one species of pest. Moreover, Trichogramma species complexes are poorly understood and entities with weak or temporary reproductive barriers may exist (sometimes induced by symbionts). Thus, released strains may hybridize with native strains, which will limit the effectiveness of biocontrol. To ensure traceability and prevent unintended effects of biocontrol programs, Trichogramma species complexes must be precisely characterized before release.

Our project has 4 major objectives : 1) Decipher Trichogramma species-limits and gene flow , 2) Understand how key traits (e.g. fecundity, reproductive success, dispersal, phototaxy) vary in relation to evolutionary history and ecological habitat, 3) Determine which individual traits can predict population establishment and functional success, 4) Contribute a comprehensive database and a reference collection for Trichogramma.

Understanding the selective pressure driving Trichogramma evolution (e.g. how strategies of host exploitation have evolved) and developing knowledge on phenotypes, hybridization potential of released strains with each others and the local fauna or on the relative influence of competition and facilitation for parasitoid communities organization should allow us to i) better select appropriate strains for targeted biocontrol, ii) maximise the chances of safely introducing agents into a new habitat and iii) better anticipate their impact and modify control strategy if needed.

Leader : J.-Y Rasplus.

People Involved : A. Cruaud, J.-Y Rasplus, G. Genson, S. Nidelet.

Partners : INRA ISA team RDLB and M2P2 Sophia Antipolis France, CNRS LBBE Lyon France.

Project founded by our National Research Agency (ANR)

more about the project

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Our contribution to the project : J.-Y. Rasplus is the project leader and, as a taxonomist, he will give other partners a leg up for the morphological identification of the trichos. We are involved in sampling and in charge of the pangenomic characterization of the different strains using RAD sequencing (i.e. the sequencing of fragments adjacent to restriction sites). As shown below (yellow bars) on a portion of the genome of T. pretiosum, in silico digestion revealed 59,433 PstI cut sites (c.a. 1 cut site every 4 kb). The sequencing of these RAD tags should allow us to i) accurately characterize entities within Trichogramma species complexes as well as possible hybridization, ii) disentangle their evolutionary relationships and iii) identify genetic markers that could be further used to select efficient biocontrol strains, especially those involved in phenotypic traits characterized by other WPs.