Mitarbeitende

The successful integration of entomopathogenic fungi into pest control strategies depends on improving application techniques, developing formulations that maintain virulence and exploring the potential of other highly virulent strains. These factors are also crucial for managing the European cockchafer (Melolontha melolontha L.), known for causing substantial damage to grassland, orchards and nurseries during severe infestations. In steep alpine meadows, the biological control of the cockchafer presents unique challenges due to the terrain, which requires the use of lightweight and slope suitable machinery. While an appropriate machine capable of injecting solutions into the soil has recently been engineered (MMexit application technique), a compatible water-dispersible fungal formulation is yet to be developed. This formulation should contain virulent propagules of Beauveria brongniartii, an entomopathogenic fungus characterised by its abundance, high host specificity and application in control of Melolontha melolontha (Kessler et al., 2004). However, a recent study by Pedrazzini et al. (2024) has challenged the commonly held belief that B. brongniartii is the most relevant pathogen of M. melolontha, instead identifying B. pseudobassiana as the revalent pathogen in adult cockchafers (Pedrazzini et al., 2024). Thus, this study has two main goals (i) to develop a dispersible formulation based on B. brongniartii to control cockchafer larvae infestations in steep alpine meadows and (ii) to reevaluate the dominant pathogen of M. melolontha larvae, thereby exploring a potential complementary approach of using B. pseudobassiana for cockchafer control. As for the development of a dispersion formulation (i), ongoing tests involve formulating fungal biomass containing a mix of mycelial fragments, blastospores and submerged conidia of B. brongniartii (BIPESCO 2) into resuspendable pellets. While the vitality of the prototype formulation was promising, the pellets exhibited poor resuspendability, prompting further trials to focus on optimising the composition of the adjuvants. Furthermore, randomised block trials, consisting of four blocks with six treatments per block (total plots per site n = 24), were conducted at two locations in Austria (Tyrol and Vorarlberg) to evaluate fungal abundance following different inoculation treatments. All liquid products were applied using the MMExit application technique. The treatments included three fungal applications: a culture broth (a mix of fungal propagules), suspended aerial conidia, and the well-established granular product Melocont™ Pilzgerste. Additionally, suspended nematodes were applied as a reference product, alongside a water application to assess the impact of the application technique, and an untreated plot. The pest pressure was determined before application and will be reassessed in spring 2025. Soil samples were taken before application, 2-3 weeks after application, and again approximately 3 months post-application. These samples are currently under evaluation. A reapplication of the products is already planned in Tyrol, as only limited application success was observed in this region. To identify the most common pathogen of M. melolontha larvae (ii) a minimum of 130 larvae were collected from three locations in Austria - Salzburg, Vorarlberg, and Upper Austria – as well as one location in Switzerland – Wallis. All grubs were kept individually in quarantine and regularly monitored for signs of infection. Upon mycosis, the fungi were isolated from the cadavers then transferred into pure culture. From the sites in Salzburg, Vorarlberg and Wallis 17 Beauveria spp., Metarhizium spp. and 29 isolates from other fungal species were collected from mycosed grubs. The larvae from Upper Austria have only recently been collected and are yet to show signs of mycosis. Thus far, these isolates have been identified based on morphological characteristics, with sequencing planned for the upcoming year to confirm species-level identification. Given the overall mycosis rate, particularly the limited prevalence of Beauveria spp. isolates, additional white grub collections from other untreated field sites will be carried out in 2025. An increased number of isolates is necessary to determine the frequency of infection by B. brongniartii and B. pseudobassiana and understand infection patterns as well as host-pathogen dynamics.