Development of attract and kill formulations for biological psyllid pest control

Psyllid pests are distributed all over the world causing damage in various crop plants by serving as vector insects of phytoplasmosis diseases. One of these psyllids present in European apple orchards is the summer apple psyllid Cacopsylla picta, which is the most important vector of Candidatus Phytoplasma mali, the causing agent of apple proliferation. As there are no direct measures to combat phytoplasmas, the vector itself needs to be controlled. The overall aim of this project was the development of attract and kill formulations that can be applied for the biological control of C. picta in apple orchards. In a former study, the sesquiterpene β-caryophyllene was identified as an attractant for C. picta by Mayer et al. (2008). In order to protect and slow the release of β-caryophyllene, a novel formulation based on an oleogel was developed. This attract formulation combines unique properties that make it highly suitable for the application and release of semiochemicals, such as a reduced processing temperature, high loading capacities, improved oil-binding capacity and mechanical stability, self-adhesive properties on leaves and release modifiability (Muskat et al., 2022 a). Pandora sp. nov. inedit (ARSEF 13372), a new entomopthoralean fungus with potential for the control of psyllids, which was isolated from an infected psyllid collected in a Danish pear orchard by Jensen et al. (2018), was selected as kill compound. In previous studies, the pathogenicity of Pandora sp. nov. has already been demonstrated for several psyllid species (Görg et al., 2021). As the mass-production of fungal biomass is essential for providing inoculant in a sufficient quantity for large scale field application, a cost-effective and scalable fermentation process for production of finely-dispersed hyphae was established to cultivate the new fungus (Muskat et al., 2022 b). The conversion of Pandora into an easily applicable form was realized by encapsulation of the hyphal biomass in Ca-alginate beads additionally providing nutrients for improved sporulation capacity. With this formulation, the two target psyllid species C. picta and C. pyri were successfully infected by Pandora sp. and killed with a mortality of up to 89 % (Muskat et al., 2022 c). To address the humidity problem, as most entomophthoralean fungi require saturated humidity conditions for efficient sporulation and conidia germination, a paste-type formulation containing bio-based superabsorbents was developed. Co-application of the beads with the paste enabled sporulation at non-saturated humidity conditions in a laboratory and a semi-field trial. Our studies form the scientific and technical basis for above-ground application of specific formulations for the control of psyllid pests by innovative attract and kill strategies.