Research

The invasive Tree-of-Heaven (Ailanthus altissima) is increasingly migrating into habitat types worthy of protection, where, due to its rapid growth, its low soil, site and climate requirements, its high capability of reproduction via root suckers and stump sprouts, its strong vegetative reproduction and massive production of seeds and due to its allelopathic properties, it endangers rare plant species and associated animal species. In the present project, an attempt is being made to combat invasive Tree-of-Heaven on the dry grassland site Dürrham (Heißlände) in the Lower Lobau, which is worthy of protection, and in the FFH habitat types 91G0 (Pannonian oak-hornbeam forest), 91H0 (Pannonian downy oak forest) and in the FFH habitat type 6210 (Trespen-fescue-limestone dry grassland) on the Bisamberg, respectively. Furthermore, soil as well as potentially susceptible dicotyledonous plants will be sampled and screened for the agent V. nonalfalfae (see below) on both sites in spring 2024 and 2025. The control is to be carried out using the biological control method developed at the Institute of Forest Entomology, Forest Pathology and Forest Protection (BOKU University) in 2011 on the basis of the native wilt fungus Verticillium nonalfalfae, which has already proven to be sustainable, cost-efficient, but also quickly and specifically effective in numerous series of experiments. The control is therefore also in line with the biodiversity strategy Austria 2030+ of the BMK.

Winter dormancy is a recurring period of suspended development and reproduction, allowing insects to survive harsh conditions. It may occur as an immediate response to adverse conditions (quiescence), or as diapause, a more complex and dynamic process. Facultative diapause is triggered by specific environmental cues that precede unfavourable conditions, typically by decreasing photoperiod. Obligate diapause is genetically fixed, independent of environmental conditions. Winter dormancy is associated with reduced activities and metabolic adjustments. The oligophagous, koinobiont endoparasitic wasp Glyptapanteles liparidis is a key natural enemy of the spongy moth, Lymantria dispar, a major defoliating pest in oak forests. Despite of a long history of research in this parasitoid-host-system, the overwintering biology of G. liparidis is still poorly understood. Eggs or first instar wasp larvae overwinter inside a caterpillar host. Since the univoltine spongy moth passes the winter months inside the egg, the multivoltine G. liparidis is dependent on alternative lepidopteran hosts that overwinter as larvae. A possible overwintering host is Lasiocampa quercus, a common species in oak forests with a wide ecological amplitude. The moth passes the winter months as early or intermediate instar larva; however, their overwintering biology has not been studied sufficiently. Our goal is to investigate the overwintering strategy of the parasitic wasp and its potential overwintering host, and whether the system might also be susceptible to asynchronicity due to changing environmental conditions. We will characterize and compare the induction, duration, and depth of winter dormancy in G. liparidis and L. quercus in laboratory and semi-field trails. Specifically, various day lengths and temperature combinations will be used in different phases of the life cycle of host and parasitic wasp. Parasitized hosts will be dissected at specific intervals to determine the developmental progress of the wasp larvae inside the host. Metabolic changes such as food consumption and feces production, oxygen consumption, the ability to supercool, and specific metabolites such as glycogen, trehalose, polyols, amino acids, and proteins will be assessed.

Maple species (Acer spp.), silver fir (Abies alba), pine species (Pinus spp.) and oak species (Quercus spp.) are regarded as promising tree species for the future, because compared to other species, particularly Norway spruce (Picea abies), they are more adapted to drought stress and increasing temperatures. However, these species can also be affected by novel pathogens and pests, some of which, as shown in recent decades, have already been increasing in importance nowadays. This “Waldfonds” project aims at clarifying the causes of emerging diseases as well as increasing and deepen knowledge on the distribution, biology and ecology of selected pathogens on the mentioned tree species. The project is divided into the following five work packages (WP): • WP 1: Diseases of maple • WP 2: Damaging organisms on fir • WP 3: Needle diseases of pine species • WP 4: Oak decline • WP 5: Knowledge transfer The project is conducted jointly in close collaboration by the Federal Research and Training Centre for Forests, Natural Hazards and Landscape (BFW), the Department of Botany and Biodiversity Research of the University of Vienna and the University of Natural Resources and Life Sciences, Vienna (BOKU).