The European Spongy moth, Lymantria dispar (L.) (Lepidoptera: Erebidae), is an abundant species found in oak woods in Central and Southern Europe, the Near East, and North Africa and is an important economic pest. It is a voracious eater and can completely defoliate entire trees; repeated severe defoliation can add to other stresses, such as weather extremes or human activities. Lymantria dispar is most destructive in its larval stage (caterpillars), stripping away foliage from a broad variety of trees (>500 species). Caterpillar infestation is an underestimated problem; medical literature reports that established populations of caterpillars may cause health problems to people and animals. Inflammatory reactions may occur in most individuals after exposure to setae, independent of previous exposure. Currently, chemical and mechanical methods, natural predators, and silvicultural practices are included for the control of this species. Various insecticides have been used for its control, often through aerial sprayings, which negatively affect biodiversity, frequently fail, and are inappropriate for urban/recreational areas. However, bioinsecticides based on various microorganisms (e.g., entomopathogenic viruses, bacteria, and fungi) as well as technologies such as mating disruption using sex pheromone traps have replaced insecticides for the management of L. dispar.

This paper provides the first detailed presentation of research and professional activities in the field of biological control in Slovenia during the period of 1990–2020. It presents information on the important pioneering role of Prof. Dr. Lea Milevoj in biological control research in Slovenia, especially in regard to the inventorying and laboratory rearing of indigenous beneficial organisms, evaluation of the influence of food type on the feeding behaviour of beneficial organisms, participation in the first introduction of a natural enemy within the context of classical biological control in Slovenia, preparation of rules on the biological control of plant pests and publication of the first Slovenian monograph on biological control. The paper also describes the activities of Slovenian researchers in regard to entomopathogenic nematodes, especially related to the assessment of their presence and efficiency in suppressing harmful insects and the identification of indigenous parasitic nematodes associated with economically harmful slugs. The paper also notes some applicative and basic research projects pertaining to parasitoids, especially in terms of their function as natural enemies of aphids, and in regard to predators of harmful insects and mites, especially predatory mites. The main goal of these activities is to implement the use of as many natural enemies as possible in food and ornamental plant production systems to replace the use of plant protection products.

In a laboratory experiment, we studied the insecticidal effects of invasive alien plants on the rice weevil. The research was carried out in two parts. In the first part, we studied the insecticidal properties of seven different plant species, namely, Bohemian knotweed (Fallopia × bohemica), Japanese knotweed (Fallopia japonica), false indigo-bush (Amorpha fruticosa), tree of heaven (Ailanthus altissima), staghorn sumac (Rhus typhina), Canada goldenrod (Solidago canadensis), and giant goldenrod (Solidago gigantea). Mixtures of powders and wheat were prepared in two different concentrations, namely, 2.5 w% and 1.25 w%. The experiment was performed at temperatures 20 °C and 25 °C and at two humidity levels, 55% R.h. and 75% R.h. Very low mortality (below 8%) was found when using combinations with the higher relative humidity. No significant differences were observed between the effects of these concentrations. In the second part of the experiment, Norway spruce wood ash and diatomaceous earth (product SilicoSec®) were added to the powder obtained by milling leaves of four different invasive plant species (Canada goldenrod, staghorn sumac, tree of heaven, false indigo). In the independent application, wheat was added to the powder at a concentration 2.5 w%. In the treatments that involved mixtures of powder and wood ash/diatomaceous earth, we applied 1.25 w% plant powder and 1.25 w% wood ash or 1.25 w% plant powder and 450 ppm of a SilicoSec® preparation. The positive control was carried out as two separate treatments with 2.5 w% wood ash of Norway spruce and 900 ppm of the SilicoSec^® product, while untreated wheat represented the negative control. The experiment was performed at two temperatures (20 °C and 25 °C) and two R.h. values (55 and 75% R.h.). The mortality of beetles was recorded on the 7th, 14th, and 21st day after the start of the experiment. Higher mortality rates of rice weevil adults were found at the higher relative humidity, and an important factor of mortality was also the day of exposure, as a higher mortality was found when the exposure of individuals to the tested substances was for a longer time period. After 21 days at 25 °C and 55% R.h., the combinations in which the lower concentration of Norway spruce wood ash was added to the powder of invasive alien plants achieved more than 90% mortality of beetles. By adding the plant powder of invasive alien plants to wood ash, we achieved a greater insecticidal efficacy of invasive plants and lower concentrations of wood ash. Nevertheless, the results of our research do not indicate any great usefulness of the plant powder of invasive plants in suppressing the rice weevil. Additional studies should primarily focus on the insecticidal efficacy of powder from the genus Solidago, which in our study, displayed the greatest insecticidal potential among the tested invasive plants.

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.