PARAsitoid based DEcision tools for insecticide use reduction against grape and wheat agrosystem pests – PARADE

These objectives will be based on the use of recently developed molecular tools precisely detecting early occurrence of parasitoids in grape-moths (Lobesia botrana) and three most abundant cereal aphids (Sitobion avenae, Metopolophium dirhodum et Rhopalosiphum padi).
The decision support tools (DST), based on a statistical model, will relate the early parasitism rates to the level of infestation and damage of pest populations. Aphid population will be considered as controlled if its rate of increase is negative (decreasing population).
For grape-moths, whose population dynamics exhibit temporally separated generations, probability for larval population at generation n+1 to exceed the economic threshold will be estimated on the basis of the population density and parasitism rate at generation n. Model fitting will be carried out using data collected in the 2021 and 2022.

An important step in this first year of the ANR Ecophyto Parade project (2021) was the setting up of two networks of plots (which will nevertheless change next year for the wheat plots) in cereal crops and vines. These plots are located in several French agricultural regions and having different cultural and environmental characteristics.
The robotic molecular detection of parasitism, developed in the first year of the project, is also an important step forward the transferring the tool to routine use. This use will reduce the time lag between early detection of parasitism and the use of this data in the statistical model of the DST.
In cereal crops, aphid numbers measured in the first year of the project on a network of 36 plots were found to be significantly higher in south-west France than in Brittany and the other regions studied. The average rate of natural parasitism of these aphids was 35.2% on all plots and was higher in Brittany (44%) than in the other regions (23%). Although no significant relationship was found at the regional level, nevertheless, all trends were clearly towards a decrease in the growth rate of aphid populations as a function of parasitism.
In vineyards, the evaluation of the level of grapevine moth populations over the three generations showed a pressure of 34.48 glomerules/100 bunches on average on all 34 plots. In the Aude region the pressure was significantly higher than in other regions, with 53.6 glomerules/100 clusters. The average rate of natural parasitism detected on the grapevine moth larvae collected in 2021 (the molecular test is being finalised) is 35%. The influence of natural parasitism on the demographic link between the three generations of grapevine moths can be evaluated as soon as the molecular analysis of the parasitism rate is finalized.

Actions to be carried out from 1 March 2022 to 30 August 2023:
(i) Complete the molecular analysis of the natural parasitism rate of grapevine moths larvae collected in 2021.
ii) The extension of the two networks (cereals and grapevine) to 40 plots for each
iii) Repeat monitoring and the sample collection for the parasitism detection rate (without any further technical development need)
All these measurements obtained in grapevine and cereal crops (2021 and 2022), will be integrated into the statistical model of the decision support tools. This model will also include data relating to agricultural management (insecticide treatment, tillage, etc.) as well as climate data.
Making farmers aware of the natural parasitism impact in pest regulation would allow them to overestimate the damages and thus to review the thresholds for insecticide use.

Dissemination of results and tools in both crops will first be based on scientific production (peer review international journals) and technical national journals. Two scientific papers are envisaged on the results of the two-year project.
Trainings and presentations of the potential of biocontrol will be provided by organizing technical meetings in different grape growing regions. The close collaboration between research groups and interprofessional organizations will guarantee efficient and rapid deployment of the outputs of our project.

ABSTRACT:
Reduction of pesticide use in crops is now becoming an urgent concern, and implementation of biological control are issues to achieve this goal. Biological control against insect pests is now used in many crops as a control strategy replacing in most cases the use of insecticides. It can be achieved either by releasing of natural enemies, or by biodiversity conservation. Farmers are more and more aware of the important role that natural enemies may play on the control of crop pests. However, the absence of any actual quantification of the potential influence of natural enemies on grape-moths and aphids population dynamics (the most damaging pests in grape and cereal crops respectively) reduced until now the inclusion of natural enemies activity in management decisions.
The present project PARADe focus on biodiversity conservation scoping on efficient parasitoids that occurs in these major crops, cereals and grapes. It involves two important INRA research units, two French Agronomy high schools (Agrocampus West and Bordeaux National School of Agricultural Sciences), two technical national structures (ARVALIS and French Vine and Vine Institute), two ‘extension services (Chambres d’Agriculture) and two important grape producer cooperatives. Originally, the two agrosystems are considered together in developing decision tools based on identical philosophy: assessing the occurrence of such parasitoids in the two crops and developing decision support tools to assist farmers in the development of agroecological pest management strategies. We thus want to predict the risk of reaching the threshold currently indicated to farmers to trigger insecticide treatment, based on the level of infestation of the plot and the rate of parasitism at the beginning of population development. These objectives will be based on the use of recently identified molecular tools able to detect with a fine accuracy, the occurrence of parasitoids in the two main pests of cereals (aphids) and grapes (grape-moths). These molecular tools will be used early in season to evaluate the damage on next insect generations and then to assist the decision ‘treating or not treating’. Non-academic and academic partners of this project will work closely to the process of model development and transfer to final users: technical papers, presentations and training sessions to growers and to cooperatives and structural adjustment of the teaching and pedagogical practices in order to integrate this innovation into academic training.