Stanislav Trdan

The invasive Halyomorpha halys is a serious pest for several fruit trees, causing millions of dollars of crop damage every year across the world’s major fruit-growing regions. Once established in an orchard, H. halys quickly becomes the predominant stink bug species and is a major season-long pest. Annual increases in the population size of H. halys have resulted in increased pest pressure and a growing risk of severe crop damage. Reliable monitoring is indispensable for H. halys control and management, providing comprehensive information on the seasonality of pest population dynamics, abundance, and interaction with the environment, and is essential for the successful implementation of integrated pest management (IPM) strategies to prevent crop damage. Our study followed the seasonal population dynamics of H. halys in three apple orchards in the Goriška region of western Slovenia over the period 2019–2021. Pherocon® Dual Panel Adhesive Traps (Trece Inc.) and pyramidal Rescue® Stink Bug Traps, both baited with Trécé lures (two-component H. halys aggregation pheromone + pheromone synergist), were used to monitor H. halys adults and nymphs weekly from late March to the end of November. Captures taken with both types of trap clearly describe the seasonal dynamics of H. halys, with the first occurrence of overwintering adults in April and May, and with two peak occurrences in adults, in the middle of summer and in the beginning of autumn, corresponding to the appearance of two generations per year in the study area. The growing trap captures observed during the 3-year monitoring period suggest that H. halys was only recently introduced to the area and that natural enemies have not yet been fully recruited. Pyramid traps captured significantly more adults and nymphs than clear sticky traps and provided accurate monitoring of H. halys life stages throughout the season. Regardless of the lower trap catches of adults and juveniles, clear sticky traps clearly displayed H. halys seasonal dynamics pattern. Therefore, their use is recommended as an early detection tool in areas where pests are not yet present, or in areas with small H. halys populations. Halyomorpha halys adult trap captures were higher in Šempeter orchards, within areas of great landscape diversity and a large share of urban land. The seasonal dynamics of H. halys over the 3-year period were closely related to weather conditions, with temperature and relative humidity as the major factors affecting population growth.

Between July and September 2021, researchers collected 100 specimens of the Spanish slug, Arion vulgaris, and dissected their cadavers to examine them for parasitic nematodes. Molecular techniques were used to identify the nematodes, which confirmed the presence of Oscheius myriophilus, marking the first recorded instance of this nematode in a gastropod host. To test the virulence of Slovenian strains of O. myriophilus and Phasmarhabditis papillosa and their effects on the feeding behavior of the Spanish slug, grey field slug (Deroceras reticulatum), and vineyard snail (Cernuella virgata), laboratory bioassays were conducted using nematodes grown in vivo. Nematodes were applied at various doses ranging from 10 to 500 nematodes/gastropod. The results showed that O. myriophilus and P. papillosa caused significant mortality (82.5% ± 2.5% at 15 °C) of the Spanish slug while being less effective against the vineyard snail and grey field slug. Nematodes were more virulent at a lower temperature (15 °C) than at the higher temperature (20 °C) tested in the experiment. Additionally, both nematode species significantly reduced gastropod herbivory. The potential use of O. myriophilus and P. papillosa as biological control agents against gastropods is discussed.

In Slovenia, only the native natural enemies of plant pests that are on the EPPO Positive List of biological control agents can be used in agricultural production to control plant pests. The List of native species of organisms for biological control, which is an important part of the Regulations on biological control, currently includes a total of 35 species of beneficial insects and mites and entomopathogenic nematodes. Compared to the number of species on the first list that was established in 2006, the number of beneficial species that Slovenian growers of food and ornamental plants can currently use in everyday practice has doubled. This is the result of intensive professional and research work in the investigation of the occurrence and distribution of natural enemy species in Slovenia, which has been systematically supported by the state for many years. Natural enemy species, which are an integral part of the EPPO Positive List of biological control agents, can be included on the list of native biological control species via a special procedure. However, many natural enemy species that are not yet included on the EPPO Positive List have been identified in the period 2007–2022. In this paper, we list 75 such species and we present 5 candidates (Cotesia glomerata [L.], Diadegma semiclausum [Hellen], Anisopteromalus calandrae [Howard], Neochrysocharis formosa [Westwood] and Kampimodromus aberrans [Oudemans]) that, in our opinion, have high potential as biological controls and will be suitable in the future for mass rearing and use in augmentative biological control.