Research

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).

The oak lace bug Corythucha arcuata (Hemiptera: Tingidae), native to North America, has already colonized millions of hectares of forests in Europe, Asia and Russia in recent years and continues to expand towards Central and Western Europe. Nymphs and adults suck on leaves and cause yellowing and premature leaf drop when trees are heavily infested. The aim of the project is to document the spread of this invasive species and to survey the current infestation of oak forests in Austria and Bulgaria. The data will be complemented by laboratory experiments on the biology and ecology of the oak lace bug, in particular generation development at different temperatures and mortality rates of overwintering imagines will be investigated. This information is critical for forecasting future damage trends. In addition, insects from the field will be examined for the presence of parasitoids and pathogens that can significantly dampen population development of the pest. A key aspect of the project is the mutual exchange of information and experience between the research groups of both countries, which will allow to fill knowledge gaps on the regulation of the population dynamics of this invasive species by abiotic (e.g. temperature) and biotic factors (e.g. natural counterparts). Translated with www.DeepL.com/Translator (free version)