Workshop on the Phosmet Phase-Out Plan: Controlling Fall Pests in Rapeseed

To keep pests away from rapeseed fields, the AltisOR project has been studying the olfactory receptors of the rapeseed flea beetle: “Smell is a key sense for insects in locating host plants, mating partners, and egg-laying sites… Odors are detected by olfactory receptors. Understanding them allows us to develop a reverse chemical ecology approach,” explained Emmanuelle Jacquin-Joly of INRAE Versailles.
  

In this project, an inventory and selection of the best ORs—olfactory receptors—were conducted in the fall and spring of 2022 and 2023. The results? The creation of an antennal transcriptome has provided a valuable resource for the scientific community; 74 ORs from flea beetles have been identified, and the most promising ones are currently undergoing functional testing.
  

To attract flea beetles to attractive plants and protect rapeseed fields, the following strategies were evaluated:
• Combining varieties with contrasting physiological characteristics to increase rapeseed resilience under insect pressure and/or climatic stress.
•    Attracting flea beetles to more attractive plants using another cruciferous crop (e.g., Chinese radish) and a so-called “trap” variety.
  

Between 2022 and 2024, 75 trials were conducted by Terres Inovia and its regional partners.
  

Results? “Regardless of the combination of target rapeseed and trap rapeseed, no mixture provides any real added value compared to the agronomically valuable variety planted alone for effectively reducing flea beetle infestations under the experimental conditions evaluated,” concludes Antoine Gaignou, research officer at Terres Inovia.
 

Mixing rapeseed with a trap crucifer is not sufficient to effectively reduce flea beetle infestations, even though Chinese radish proves to be more attractive to flea beetles than rapeseed within the mixture.
  

While research on evaluating varietal and interspecific mixtures for managing fall rapeseed pests at the plot level will not be continued, exploiting flea beetle preferences remains a promising avenue. “Other studies are exploring complementary strategies, including the use of companion plants and volatile organic compounds (VOCs), aimed at both disrupting insect behavior within the plot and diverting them on a regional scale,” summarizes Antoine Gaignou.
 

In this project, the research aimed to:
• Identify companion plants that influence the behavior of the
flea beetle• Determine which behavioral stages they affect•
Identify attractive
volatile organic compounds (VOCs)• Test their potential for diverting the flea beetle away from
rapeseed crops•    Combine these behavioral levers with other agroecological levers to propose a comprehensive strategy for managing the flea beetle in the short and medium term
 

The research focused on several trap crops: brown mustard, Chinese cabbage, radish, Chinese radish, forage radish, Abyssinian mustard, and turnip, under controlled and semi-controlled conditions in experimental plots. Results? “Across all tests in the various setups, three trap crops proved more attractive to the flea beetle than rapeseed: Chinese cabbage, Chinese radish, and, above all, turnip rape, which was selected for further experiments,” explains Anne-Marie Cortesero of INRAE.
  

Following this research, co-design workshops were organized in the Centre and Île-de-France regions to develop flea beetle management strategies with farmers, with the aim of facilitating farmers’ adoption of these attractant plants.
  

What are the key takeaways?
•    Attractive compounds emitted by these service plants were identified in the project and tested in the field•
The results are encouraging but need to be supplemented by laboratory work to identify the best compounds to combine and the most effective
doses• Additional field work is also planned to test the attractiveness of these VOCs under real-world conditions and determine the conditions for their effectiveness
 

Work is continuing within the METASERV and ARDECO projects.
  

Other research, conducted as part of ^the Adaptacol² project, involved “diverting winter flea beetles (and CBTs) away from rapeseed fields by attracting them to cover crop fields,” explains Céline Robert, a research officer at Terres Inovia. 

To evaluate the technique’s effectiveness, 43 partnership-based trials were set up. “The effectiveness was demonstrated because up to 77% of the flea beetles were diverted—30% on average—under these conditions, which were not always optimal.” This strategy therefore reduces flea beetle populations in the current year and the following year. 

This approach—which is inexpensive, costing between €1 and €3 per hectare—can complement plot-level strategies (such as hardy rapeseed) and is most effective when implemented at the regional level.
  

In the medium to long term, effectiveness could be enhanced through the use of chemical mediators (PARSADA ARDECO project). Research and the deployment of controlled trap crops will continue within the framework of the Dephy Expe CONCERTO and PARSADA ALTIFAST projects.