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 fly
was initially identified in Switzerland (1988) and Italy (1991), from where it spread to at least seven
additional countries (France, Spain, Germany, Austria, Croatia, Slovenia and Hungary). Rhagoletis
completa has not reached the limits of its potential distribution. Walnut trees are widely distributed in
Europe 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 Rhagoletis
completa is present and uncontrolled, 100% of walnut trees can be infested, causing losses in walnut
yields of up to 80%. The negative effect is low (<10% yield loss) under phytosanitary control, although
additional 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. Directive
2009/128/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 walnut
orchards. This pheromone-based control strategy is currently being tested in the field, thank to a close
association with an industrial partner. This pesticide-free biological product should allow a reduction
of the damages caused by the walnut husk fly.