Trap crops and entomopathogenic fungi can provide partial solutions for integrated pest management, by attracting and killing insect pests, respectively, but both solutions have some limitations restricting their practical field applications. Both solutions have been tested against a major soil-borne pest of brassicaceous vegetables, the cabbage root fly Delia radicum. Chinese cabbage is very attractive to this pest, but it is also a high-quality host plant for developing larvae of D. radicum, which limits the application as a trap crop in the field. The entomopathogenic fungus Metarhizium brunneum can infect D. radicum larvae in the soil, but M. brunneum has not proved to be sufficiently effective in reducing damages caused by cabbage root fly. In the present work, we evaluated whether the entomopathogenic fungus M. brunneum can be used to regulate D. radicum populations together with trap crops by inoculating Chinese cabbage and broccoli plants at sowing with M. brunneum colonized rice grains before transplantation of small plants to field soil. The evaluation was performed under natural fly infestation. In both plant treatments, D. radicum infestations were high with no or only moderate effect of the fungus inoculation on the number of larvae and pupae recorded, despite evidence of successful fungal infections. On broccoli plants, our results clearly demonstrated that the M. brunneum application was inefficient in reducing number of D. radicum stages in the soil and resulting plant mortality. However, in the trap crop, Chinese cabbage, M. brunneum inoculation reduced the number of D. radicum imagos emerging from the plants by 36%. Hence, the strategy is likely to have effects on the next D. radicum generation. This result is the first to indicate complementarity between the 'attract' and 'kill' strategies to control pest development inside a favorable trap crop and prevent future pest population outbreaks. Also, from both plant inoculation treatments, some emerging D. radicum imagos developed M. brunneum infection, which may assist the transmission of the entomopathogenic fungus among adult populations.

Urban environments are vulnerable to the introduction of non-native species and sometimes contribute to their invasion success. Knowing how urban landscape features affect the population dynamics of exotic species is therefore essential to understand and manage these species. The spotted-wing drosophila, Drosophila suzukii, is a highly polyphagous fruit fly that has become a very problematic invasive species over the last decade. Because of its important damage on fruit production, D. suzukii populations have mainly been studied in agricultural areas, while their dynamics in urban landscape remain poorly explored. The objective of this study was to investigate the role of urban environment in the invasion success of D. suzukii by identifying local and landscape factors driving the abundance of the fly along seasons and urbanization gradients. To achieve this, 526 insect traps were randomly set in four different habitats (urban forest, park, riverside and town centre) along an urbanization gradient in the city of Amiens (France), between September 2018 and August 2019. The influence of landscape and local environmental variables on Drosophilidae species diversity and composition was examined using GLM and multivariate analyses. We found that Drosophilidae species richness and abundance were negatively impacted by urbanization. The Drosophilidae community was dominated by D. subobscura and D. suzukii, but their relative abundance varied with seasons. Drosophila suzukii used urban forest during winter and also during heat waves in summer. The fly was still active in this habitat in winter when the ground was covered with snow. The cover of brambles, shrubs, soil litter and dead wood debris were identified as valuable ecological indicators of the presence of D. suzukii. We highlight the role of the different components of urban environment in the ecology of D. suzukii, particularly with regard to its winter survival. These results could serve for designing management strategies in urban habitats in order to reduce the invasion success of D. suzukii.

Soil-dwelling insect pests may cause considerable damage to crops worldwide, and their belowground lifestyle makes them hard to control. Amongst the most promising control agents for subterranean pests are soilborne entomopathogenic fungi (EPF) such as Metarhizium brunneum. Albeit EPF can be highly pathogenic to their target pest species under laboratory conditions, their efficacy in the field is often limited due to adverse environmental conditions. Here, we test for the first time if the efficacy of EPF can be improved when they are augmented with trap crops. In a field experiment, the M. brunneum strain ART2825 was combined with a trap crops mixture of six plant species and evaluated for its control effect of wireworms (Coleoptera: Elateridae). When both were combined in the main crop, potato damage was lowered on average by 42.5% and wireworm abundance by 50.8%. Single application of trap crops or EPF lowered damage/pest abundance only by 29.9%/15.89% and 34.7%/4.77%, respectively. Importantly, the strength of the synergistic pest control effect between trap crops and EPF increased disproportionately with increasing wireworm abundance. However, DNA-based gut content analysis showed that wireworms' feeding preferences were not shifting toward the trap crops. Our findings demonstrate that combining trap crops with EPF improves the efficacy of the latter and leads to a synergistic control effect which magnifies with increasing wireworm abundance. Hence, the synergistic effect of EPF and trap crops might be a promising control strategy for soil-dwelling pests in general and significantly improve our abilities to manage soil pests environmentally friendly.