The walnut husk fly invades Europe: Risk analysis and development of a biological control strategy

Rhagoletis completa is a fly native to California that invaded Western Europe in the late 1980s. The flywas initially identified in Switzerland (1988) and Italy (1991), from where it spread to at least sevenadditional countries (France, Spain, Germany, Austria, Croatia, Slovenia and Hungary). Rhagoletiscompleta has not reached the limits of its potential distribution. Walnut trees are widely distributed inEurope favouring the probability of fly establishment in currently fly-free areas.Since its introduction in Europe, it causes important damage to walnuts. In orchards where Rhagoletiscompleta is present and uncontrolled, 100% of walnut trees can be infested, causing losses in walnutyields of up to 80%. The negative effect is low (<10% yield loss) under phytosanitary control, althoughadditional costs must also be considered to support specific monitoring for Rhagoletis completa.Europe aims at reducing the amount of phytosanitary products in its territory (e.g. Directive2009/128/CE), resulting in the necessity to develop environment-friendly methods of pest control.After a 4-year research project conducted jointly in Gembloux Agro-Bio tech (Belgium) and in Chatte(France), we have proposed a new biological method to monitor and control walnut husk flies in walnutorchards. This pheromone-based control strategy is currently being tested in the field, thank to a closeassociation with an industrial partner. This pesticide-free biological product should allow a reductionof the damages caused by the walnut husk fly.