Chemical control of Popillia japonica adults on high-value crops and landscape plants of northern Italy

The introduction of the Japanese beetle (Popillia japonica Newman) in Italy raised concerns for its control in herbaceous and perennial crops, nurseries and landscape plants. During the early stages of spread of an invasive pest, the availability of effective insecticides is essential to sustain the immediate needs of plant protection. Here, we screened the effects of 20 active ingredients representative of chemical and organic insecticides registered in Europe for adult beetle management on high-value crops (grapevine, peach and corn) and landscape plants (willow and Virginia creeper) by field trials carried out in 2019 and 2020. Plant parts suitable for spraying were sleeved and beetles were caged before the application (contact effect), after the application but on the same day (residual, short-term effect), and 7-8 days after the application (residual, long-term effect). Among the 20 active ingredients tested, only four broad-spectrum (acetamiprid, deltamethrin, lambda-cyhalothrin and phosmet) were effective in killing beetles under all the experimental conditions, while other broad-spectrum and selective ingredients were mainly effective only on contact and as short-term residual. The organic active ingredients were much less effective under any condition. The data provide a valid support to update the European guidelines aimed at controlling P. japonica for growers, landscape managers and homeowners. The low selectivity of the most effective insecticides requires the integration into management strategies that envisage their use only whether strictly necessary, and in combination with other containment measures.