Trichogramma brassicae is frequently used as a biological control agent (BCA) against the European corn borer, Ostrinia nubilalis. Its wide use and its economic importance rank it as a suitable case study for selection programmes in order to obtain populations with increased fitness and field efficiency. Paving the way for such a programme requires the exploration and characterization of the intraspecific diversity that may be used as a basis for a selection programme.
During the course of the project, the mixed INRA-IAS-PUC R&D team have investigated the intraspecific diversity in T. brassicae as BCA. First, the T. brassicae diversity in Europe was explored by sampling different regions and countries (Croatia, Moldavia, France…). Crosses between population samples were performed in order to increase variability in a single large laboratory population. From this large laboratory population, several laboratory strains (isolines) were created from one female. Then, several protocols were implemented in order to study different phenotypic traits in the isolines including walking activity, flight activity, host detection capacity, oviposition behaviour, fecundity and longevity.
After that, the same isolines were field-released to characterize their dispersion and efficacy, and correlate traits measured in the laboratory and in the field. More precisely, artificial patches of Ephestia kuehniella eggs were used to study dispersal behaviour of 11selected isolines in maize field. All strains were introduced in the field at the same time. At final, six spatial repetitions and three temporary repetitions were carried out. In parallel, the isolines genotype was characterized by 16 microsatellite markers.
The results obtained shown that they are a high intraspecific variability between lines, not only in laboratory test, but also in the field test. In fact, thanks to the microsatellites kit developed by the mixed team INRA-IAS, it was possible to distinguish the different lines of Trichogramma after releasing them in the field and then to analyse precisely their dispersion pattern. Some strains showed good dispersion and parasitism patterns in the field, suggesting a more efficiency and thus the development of a new Trichogramma product for IAS.