Non-target effects of ten essential oils on the egg parasitoidTrichogramma evanescens

Abstract

Essential oils (EOs) are increasingly used as biopesticides due to their insecticidal potential. This study addresses their non-target effects on a biological control agent: the egg parasitoid Trichogramma evanescens. In particular, we tested whether EOs affected parasitoid fitness either directly, by decreasing pre-imaginal survival, or indirectly, by disrupting parasitoids' orientation abilities. The effect of Anise, Fennel, Sweet orange, Basil, Coriander, Oregano, Peppermint, Mugwort, Rosemary and Thyme EOs were studied on five strains of T. evanescens. Specific experimental setups were developed, and data obtained from image analysis were interpreted with phenomenological models fitted with Bayesian inference. Results highlight the fumigant toxicity of EOs on parasitoid development. Anise, Fennel, Basil, Coriander, Oregano, Peppermint and Thyme EOs are particularly toxic and drastically reduce the emergence rate of T. evanescens. Most EOs also affect parasitoid behavior: (i) Basil, Coriander, Oregano, Peppermint, Mugwort and Thyme EOs are highly repellent for naive female parasitoids; (ii) Anise and Fennel EOs can have repellent to attractive effects depending on strains; and (iii) Sweet orange, Oregano and Rosemary EOs have no detectable impact on orientation behavior. This study shows that EOs fumigation have non-target effects on egg parasitoids. This highlights the need to cautiously precise the deployment framework of biopesticides in an agroecological perspective.

Non-target effects of ten essential oils on the egg parasitoid Trichogramma evanescens

“…However, Anise and Fennel EOs set apart, probably because they both are mainly composed of anethole, known to exhibit insecticidal activity (Dunan et al, 2021;Sousa et al, 2021). Furthermore, Rosemary and Thyme EOs also distinguish themselves since they are heterogeneous (several major constituents) contrary to the other homogeneous EOs, that are mainly composed of a single majority component (>50%, Table S.1 in Louise Van Oudenhove, Cazier, et al (2022)).…”

“…The exposure chamber was hold firmly closed with eight pliers (Fig 2). Air circulation inside the exposure chamber has been modelized with Computational Fluid Dynamics to check that the airflow was laminar (see Supplementary Information S.2 in Louise Van Oudenhove, Cazier, et al (2022) for details). This result was confirmed experimentally with smoke tests that show a smooth and regular repartition of the smoke inside the exposure chamber.…”

“…for each strain j. All Parameters were estimated with Bayesian inference from non-informative priors (see Supplementary Information S.3.1 in Louise Van Oudenhove, Cazier, et al (2022) and script Survival_Step1.R in L. Van Oudenhove (2022) for details). From these estimations, both the number of black and white eggs (EggsB and EggsW) were predicted from the number of pixels for all patches (see Supplementary Information S.3.1 and Burte et al (2022) for prediction accuracy).…”

“…A conceptual model that describes how essential oil affect parasitoid development was built (see Supplementary Information S.3.2 in Louise Van Oudenhove, Cazier, et al (2022) for details). This model includes two steps: (i) parasitism and parasitoid pupation: Are parasitoid eggs laid in the host eggs and do they develop into pupae?…”

“…To estimate the parameters of these models, we performed Bayesian inference (details are provided in the Supplementary Information S.3.2 in Louise Van Oudenhove, Cazier, et al (2022), and the script Survival_Step2.R is deposited in L. Van Oudenhove ( 2022)). We tested different possibilities for both parameters α i,j and β i,j to study the influence of the EO and the specifity of the strain (Table 2).…”