Soutenance de thèse - Antoine PASQUIER

devant le jury composé de :

Président du jury :

• Anne-Marie Cortesero : Professeur, Université de Rennes, France 

Rapporteurs :

• Outreman Yannick : Professeur, Agro-campus Ouest, France
• Gard Benjamin : Ingénieur de recherche, CTIFL, Bellegarde, France
• Toepfer Stefan : Directeur de recherche, CABI, Hongrie. 

Examinateur : 

• Cortesero Anne-Marie : Professeur, Université de Rennes, France 

Invité :

• Andrieux Thibault : Ingénieur de recherche, Bioline Agroscience 

Directeurs de thèse :

• Vercken Élodie : Directrice de recherche, INRA UMR 1355, Sophia Antipolis, France

Abstract :

Maize is the most important cereal crop in the world (162 million hectares). It plays a major role in human and animal nutrition and its cultivation occupies about 9% of the useful agricultural area in Europe. Since its arrival in Europe in 1992, the corn rootworm, belonging to the order Coleoptera, has threatened this important crop. The larval stage of this organism is particularly harmful to plants because it attacks the underground parts of this cereal causing yield losses that can reach 80% of the crop's potential in the most critical cases. Chemical pesticides, the use of Bt GMOs and crop rotation alternating soybeans and corn are the main control methods for this pest currently. However, studies have shown that some populations are resistant to these insecticides and are able to (i) persist in the soil longer and (ii) expand their host range by attacking soybean roots. In this context, there is a need to explore new crop protection methods that will allow a more integrated control of this pest. A study recently demonstrated the potential role of soil predatory mites as biological control agents. These organisms are at the top of trophic chains in agricultural systems and have already shown strong abilities to control populations of subterranean pests. The main objective of my thesis is to develop a biological control strategy agronomically  and economically viable to control corn rootworm. First, I evaluated the predation capacity of three soil mites (Stratiolaelaps scimitus, Gaeolaelaps aculeifer and Macrocheles robustulus) on the early developmental stages of western corn rootworm in the laboratory. These results were conclusive and one of the three candidates particularly attracted our attention: G. aculeifer. This predatory mite showed a higher predation capacity on the first larval stage of the pest.  In a second step, I studied the effect of the presence and the density (100, 500 and 1000 mites per corn plant infested by the pest) of these predatory mites on the western corn rootworm population under semi-controlled conditions.This experiment showed that the mite densities tested were all effective in protecting the maize plant. Finally, and in order to optimize the effectiveness of these predatory mites as a biocontrol agent, I studied the population dynamics of these predators when a low density of predatory mites has been introduced at the time of seeding (Predator-in-first method) and in the presence of alternative food, in a field naturally infested by corn rootworm. These experiments allowed me to identify an application method that would facilitate the introduction of the biological control solution and reduce its cost. My work will provide essential information in understanding the biological control potential of these previously understudied soil organisms. 

Keywords : Predatory mites, Gaeolaelaps aculeifer, biocontrol, predator-in-first