Wolfgang Völkl (1960 - 2015)

This page is dedicated to the memory of Wolfgang Völkl and the contributions he made to a number of fields, ranging from the behavioural, population and community ecology of insects to questions of conservation. Wolfgang Völkl was a rare case of a scientist with a firm background in the natural history of many organisms, who used his observations of living organisms to derive novel hypotheses, which he subsequently put to test using carefully designed field and laboratory experiments. His main interest was to explain patterns in community and population ecology by linking them to the behaviour of the interacting species. Many of the phenomena that Wolfgang Völkl discovered were subsequently analysed in more molecular detail by fellow scientists in the laboratory, e.g. mechanisms of chemical mimicry. His initial work was, however, vital to start those lines of research. Scientific progress in ecology starts with the detection of patterns in nature, and Wolfgang Völkl was one of those ecologists who contributed many observations of plant-insect, insect-insect, and more generally, animal-animal interactions to science. He was a great admirer of the work of Jean-Henri Fabre, the French naturalist who pioneered the observation of living insects, and painstakingly documented their behaviour. Wolfgang Völkl was similar to Fabre in the importance he paid to behavioural observations.

Wolfgang Franz Völkl was born on 21. April 1960 and grew up in Bärnreuth, a small village near Bad Berneck in the Fichtelgebirge near Bayreuth. Until German re-unification in 1990, this area, Upper Franconia (Oberfranken), was one of the remote places in West Germany, as it bordered to Czechoslovakia in the East, and to the German Democratic Republic (DDR) in the North. Population density in this hilly area was low. Forests and grasslands dominated the area, and, among natural habitats, bogs. Wolfgang Völkls love of nature started when he was a child, where he spent a large part of his time outdoors, and derived from his own curiosity, as neither his parents or relatives had any strong tradition in nature observation or conservation. After elementary school in Bad Berneck (1966-1970) he went to secondary school (Graf-Münster-Gymnasium) in nearby Bayreuth, where he also graduated in 1979. Here, his love for biology was fostered by his biology teacher, who also suggested to him to study biology rather than forestry, which Wolfgang had considered towards the end of his school time.

After the then obligatory one-year military service he started his studies in Biology at the University of Bayreuth in the winter 1981. Bayreuth University had only been founded in 1972 as one of the political measures aimed at supporting the declining areas along the German border to Eastern Europe. Fortunate for Wolfgang, the Biology and Geoecology departments at Bayreuth specialized in Ecology and were a hotspot for ecological research in Germany in the 1980s. A number of internationally known scientists (e.g. Ernst-Detlef Schulze, Helmut Zwölfer, Wolfgang Zech, Erwin Beck) worked in Bayreuth, connecting the rather remote and small university to the rest of the scientific world.

In his studies, Wolfgang quickly specialized in ecology and started to work as a student helper in the Department of Animal Ecology of Helmut Zwölfer. The Zwölfer group specialized on investigated plant-insect interactions, focussing on insects in the flowerheads of thistles (Asteraceae: Cynareae) (Zwölfer 1988). In addition to helping collecting thistles and rearing Tephritid flies (Diptera: Tephritidae, fruit flies) and their natural enemies, Wolfgang worked as a student helper for Dirk Stechmann, who was interested in the biological control of aphids, mainly cereal aphids. This work gave him first insights into the biology of aphid predators and aphid parasitoids, i.e. parasitic wasps of the specialized sub-family Aphidinae of braconid wasps, that reproduce by laying eggs into living aphids. Wolfgang formally joined the Animal Ecology group and combined his new expertise on aphids with the focus on thistles of the department, i.e. he started to work on thistle aphids. His Diploma thesis under the supervision of Dirk Stechmann “Investigations on the biology of thistle aphids (Homoptera), their natural enemies and mutualistic ants in Upper Franconia)”, was completed in 1986 (Völkl 1989).

After graduation, Wolfgang joined Dirk Stechmann on a 3-months trip to Tonga, to work on the biological control of the banana aphid, Pentalonia nigronervosa Coq. The aim was to introduce the aphid parasitoids Lysiphlebus testaceipes (Cresson) and L. fabarum (Marshall) to Tonga, and to test the suitability of these and other species for biocontrol (Völkl et al. 1990, Stechmann & Völkl 1990). While the introduction of the species was successful, Wolfgang noticed the importance of ant-aphid interactions for the success of aphid biocontrol – when aphids were tended by ant species that viciously attacked all aphid natural enemies including the supposed control agents, biocontrol will not work (Stechmann et al. 1996). These interactions between aphid, ants, and aphid natural enemies became an important theme of his work.

Ecology at the University of Bayreuth was booming in the 1980s and ecological research was supported by funding of the German Science Foundation (DFG) in the form of a collaborative research centre (SFB 137 ¹). This enabled Wolfgang to start, in 1986, a PhD entitled “Reproductive strategies of aphid parasitoids (Hymenoptera: Aphidiidae): consequences of their interactions with hosts and ants”, under the supervision of Helmut Zwölfer. He thus stayed at the Department of Animal Ecology, where he had in the meantime met his future wife, Maria Romstöck, also a keen insect ecologist.

¹ Gesetzmäßigkeiten und Strategien des Stoffumsatzes in ökologischen Systemen

In his Ph.D., Wolfgang investigated how the behaviour and life-history of aphid parasitoids can be understood by the constraints imposed by aphid behaviour, ant-aphid interactions, and the predation pressure of aphid natural enemies including aphid hyperparasitoids, i.e. other wasps species that reproduce by laying eggs on the larvae or pupae of the aphid parasitoids (cf. Sullivan & Völkl 1999). Starting with surveys on the occurrence of Aphis fabae on creeping thistle, Cirsium arvense (L.),  and aphid rates of parasitisms by two of the main parasitic wasps, Lysiphlebus cardui (Marshall) and Trioxys angelicae (Haliday), he proceeded to perform a suite of behavioural experiments exposing individual parasitoids to different settings. This work produced a number of very interesting findings. Most spectacular, he found that the parasitoid Lysiphlebus cardui was not attacked by ants, as the ants mistakenly took them for being aphids. Wolfgang suspected that the parasitoids used chemical mimicry (which was later proven by cuticular analysis, Liepert & Dettner 1993), and also showed that the cryptic behaviour of the species with slow movements and long (20 seconds) oviposition times, contributed to the ability of this parasitoid to exploit ant-tended colonies. Other parasitoids such as Trioxys angelicae are attacked by ants, and couple fast movements with short oviposition times (1-2 seconds) to be able to lay a few eggs into an aphid colony. In addition, they mainly attack aphids not tended by ants. Rates of parasitism at the aphid colony level (Trioxys: few aphid parasitized, independent of aphid colony size; L. cardui: up to 100% parasitized, more eggs laid in larger colonies) can thus be explained by the behaviour of the species. In one of the main papers resulting from the thesis (Völkl 1992), that continues to be cited, he showed that the parasitoid L. cardui actually profits from ant attendance, as ants also attack the aphid hyperparasitoids that endanger the larvae of L. cardui. Aphids parasitized by L. cardui, while living, produce more honeydew than unparasitized aphids, intensifying ant tending and increasing protection. In contrast, T. angelicae suffered from high rates of hyperparasitism. Thus, the different patterns of occurrence of aphids, ants aphid parasitoids and hyperparasitoids in the field, as well as levels of parasitism, can be explained by the behaviours of the interacting species. This way of explaining population-level patterns by understanding the behavioural interactions of species became a main theme in the work of Wolfgang Völkl. During his Ph.D. he became to know Prof. Manfred Mackauer of Simon Fraser University in Vancouver, Canada, who had visited Bayreuth before. Prof. Mackauer was in expert in aphid parasitoid taxonomy, and also explored the interaction between aphids and their parasitoids in careful laboratory experiments. In 1988, Wolfgang stayed for several weeks at Simon-Fraser-University. This visit was the start of a long and fruitful collaboration.The dissertation was handed in in 1990 and passed with distinction (“summa cum laude”). Wolfgang immediately started a position at Federal Research Institute for Nature Protection and Landscape Ecology in the Department of Prof. Josef Blab. Conservation had always been an interest of Wolfgang Völkl and this prestigious position strongly appealed to him. He moved to Bonn with his family, now including his first son Johannes (*1990), and became involved in a number of studies, e.g. on efficiency control in conservation (Blab and Völkl 1994). In the end, however, he only stayed about 2.5 years at the Institute, despite the fact that he was given a lifetime position. One of the reasons was that the institute at that time had already started to reduce research in its portfolio and concentrated on administrating conservation in Germany (today’s name ‘Bundesamt für Naturschutz, BfN’ is conspicuous for the absence of the word ‘research’). A more important reason was, however, that he himself felt uneasy to live far away from Upper Franconia. These factors led him to take up the position of a research assistant back at the group of Helmut Zwölfer in Bayreuth, where he stayed from 1993 to 2002. His second son, Matthias (*1993), was born soon after he returned to Bayreuth.

During his time as assistant at the University of Bayreuth Wolfgang continued his work on parasitoid reproductive strategies, but extended the range of species to those attacking various trees. In November 1997 the completed his habilitation at the University of Bayreuth entitled “From individual behaviour to population dynamics: optimal foraging in aphid parasitoids”. An overview of his achievements is given below, in the ‘main findings’ section. Prof. Zwölfer retired in 1996 and the insect physiologist Prof. Klaus H. Hoffmann took over the Chair of Animal Ecology. Wolfgang Völkls position was, however, continued as Prof. Hoffmann, as Völkl’s expertise as ecologist was still needed, and because his work was widely appreciated by the group including Prof. Hoffmann.

Wolfgang Völkl’s work increasingly diversified during this second time at Bayreuth, to also include questions of conservation. Together with the regional water authorities, he carried out a large restoration project of the river Main in Upper Franconia, that assessed the impact of this restoration on a number of organisms including plants, birds, and spiders. One other group of species where he was always interested in were reptiles, in particular the adder (Vipera berus berus L.). One project carried out at the river Lech aimed to find conservation measures for the adder, the Smooth snake (Coronella austriaca Laurenti), and the Slow worm (Anguis fragilis L.), based on studies of habitat choice and reproductive biology of these species.

After his habilitation, Wolfgang applied to various open professorships. He was offered a position at Graz, Austria, which he eventually declined. After his contract at Bayreuth expired, he and his family decided to stay in the area and continue to work in the area by founding an ecological consultancy specialized on conservation projects.