Programme REID 2012x - Inra

ANTAGONISM OR SYNERGISM BETWEEN TWO NATURAL ENEMIESOF AN INVASIVE BRASSICACEAE?M-C Bon 1 & A Caesar 21 European Biological Control Laboratory USDA-ARS, Campus International de Baillarguet,St. Gély du Fesc2 USDA-ARS Pest Management Research Unit, Sidney, USA.Natural enemies are known to affect host plant fitness through competitive interactions amongthemselves. Some plant species acquire multiple feeding guilds of natural enemies and they mayexperience various degrees of top-down regulation of their populations. Interactions among highertrophic levels of the natural enemies are common in nature as they exploit the same plant tissues.Therefore, intra-guild interactions may influence efficacy of biological control agents under fieldconditions. These interactions can be direct, for instance, insects may vector plant pathogens orindirect, where alteration of plant tissues by one may affect the survival and performance of theother organism. These interactions between microorganisms, fungi in particular, and insects mayrange from antagonistic to synergistic. However, these interactions as an area of classical biologicalcontrol research have not been fully considered when selecting new agents. The root galling weevil,Ceutorhynchus assimilis, (Coleoptera: Curculionidae) and the non-sporulating root rotting fungus,Rhizoctonia sp. are two natural enemies of the perennial and Eurasian weed, Lepidium draba spdraba (Brassicaceae). This weed is highly invasive and noxious in the central and western U.S. and sofar, biocontrol agents are lacking. The objective of the present study is to test the hypothesis thatthe combined effect of the weevil and the pathogen would suppress performance of the weed ascompared to the simple effects of an insect galling or a pathogen-infection alone. The framework ofthis study carried out in France is presented here.Mots-clés : Biological control, galling insect, root pathogen, interactions45