Dinka Matošević

Geometrid outbreak waves travel across Europe

We show that the population ecology of the 9- to 10-year cyclic, broadleaf-defoliating winter moth (Operophtera brumata) and other early-season geometrids cannot be fully understood on a local scale unless population behaviour is known on a European scale. Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article. Data cover six decades from the 1950s to the first decade of twenty-first century and most European countries, giving new information fundamental for the understanding of the population ecology of O. brumata. Analyses on epicentral, regional and continental scales show that in each decade, a wave of O. brumata outbreaks travelled across Europe. On average, the waves moved unidirectionally ESE-WNW, that is, toward the Scandes and the Atlantic. When one wave reached the Atlantic coast after 9-10 years, the next one started in East Europe to travel the same c. 3000 km distance. The average wave speed and wavelength was 330 km year(-1) and 3135 km, respectively, the high speed being incongruous with sedentary geometrid populations. A mapping of the wave of the 1990s revealed that this wave travelled in a straight E-W direction. It therefore passed the Scandes diagonally first in the north on its way westward. Within the frame of the Scandes, this caused the illusion that the wave moved N-S. In analogy, outbreaks described previously as moving S-N or occurring contemporaneously along the Scandes were probably the result of continental-scale waves meeting the Scandes obliquely from the south or in parallel. In the steppe zone of eastern-most and south-east Europe, outbreaks of the winter moth did not participate in the waves. Here, broadleaved stands are small and widely separated. This makes the zone hostile to short-distance dispersal between O. brumata subpopulations and prevents synchronization within meta-populations. We hypothesize that hostile boundary models, involving reciprocal host-herbivore-enemy reactions at the transition between the steppe and the broadleaved forest zones, offer the best explanation to the origin of outbreak waves. These results have theoretical and practical implications and indicate that multidisciplinary, continentally coordinated studies are essential for an understanding of the spatio-temporal behaviour of cyclic animal populations.

Phoretic mites of three bark beetles (Pityokteines spp.) on Silver fir

The species composition and abundance of phoretic mites of the bark beetles Pityokteines curvidens, P. spinidens, and P. vorontzowi on Silver fir (Abies alba) were investigated in 2003 at two locations (Trakoscan and Litoric) in Croatia. Stem sections and branches from A. alba trees infested by Pityokteines ssp. were collected and incubated in rearing cages. Bark beetles emerging from the stem sections and branches were examined for photetic mites. A total of ten mite species were documented for the first time as associates of Pityokteines spp. on A. alba. These included Dendrolaelaps quadrisetus, Ereynetes scutulis, Histiostoma piceae, Paraleius leontonychus, Pleuronectocelaeno japonica, Proctolaelaps hystricoides, Schizostethus simulatrix, Tarsonemus minimax, Trichouropoda lamellose, and Uroobovella ipidis. T. minimax was the most frequent phoretic mite of all the three scolytines and U. ipidis was also common, whereas, the other mite species occurred less frequently. The species spectrum and relative abundance of mite associates were similar for all three Pityokteines species. Another species, Pleuronectocelaeno barbara was commonly found phoretic on P. curvidens, captured in pheromone traps in 2005 at the location Litoric. Furthermore, two previously collected mite specimens from Switzerland, phoretic on P. curvidens, were identified as Nanacarus sp. and Bonomia sp. The records from Croatia and Switzerland in the present study increase the number of known mite associates of Pityokteines spp. from one previously documented species to 14 species. None of the phoretic mites found in the survey in Croatia appear to have the potential to be used for biological control of Pityokteines spp., although the feeding habits are unknown for many species recorded.

Climate Warming and Past and Present Distribution of the Processionary Moths (Thaumetopoea spp.) in Europe, Asia Minor and North Africa

Pine processionary moth, Thaumetopea pityocampa, is a model insect indicator of global warming, the northwards and upwards range expansion of this Mediterranean species being directly associated with the recent warming up. The knowledge about the drivers of moth expansion is synthesized. A first standardized mapping of the northern expansion edge, from Western Europe to Turkey, is presented, then detailed for 20 countries of Europe, Asia Minor and North Africa, including future trends. Additional data about the responses of the other Thaumetopoea species are given. Finally, the chapter points out the importance of the man-mediated introductions in the expansion process.

Success of classical biocontrol agent Torymus sinensis within its expanding range in Europe

Torymus sinensis Kamijo (Hymenoptera, Torymidae), a classical biocontrol agent of chestnut gall wasp Dryocosmus kuriphilus (Hymenoptera, Cynipidae), was released in Croatia, Slovenia and Hungary in 2015. Following the introduction, the research of parasitism rates and population genetic indices on 40 different sites was performed to monitor and evaluate the success of establishment. The observed parasitism rates were unexpectedly high and negatively correlated with the distance from westernmost locality, while population genetic indices showed that populations of T. sinensis did not suffer from bottleneck‐induced founder effect phenomenon. Moreover, lack of genetic differentiation demonstrates that all populations share similar genetic structure, which could be shaped only by high levels of gene flow. We conclude that T. sinensis established viable and genetically diverse populations and successfully spread naturally from Italy across Slovenia to Croatia and Hungary.

The Asian chestnut gall wasp Dryocosmus kuriphilus : a global invader and a successful case of classical biological control

Native to China, the Asian chestnut gall wasp, Dryocosmus kuriphilus (ACGW), was first found outside its native range in Japan and the Korean peninsula in the mid-twentieth century. After appearing in North America in 1974, it was found in Europe a few decades later. Since then, the gall wasp has spread throughout the distribution of chestnut in Europe. The ACGW’s discovery in North America and Europe elicited numerous studies to understand its invasive potential in these areas and how to control its spread and impact on chestnut production. Although endemic parasitoids responded positively to D. kuriphilus with low parasitism rates, the most effective management tactic has been classical biological control via the introduction of the parasitoid Torymus sinensis from its native range in China. This review summarizes the history of introduction, spread, and current distribution of D. kuriphilus, and highlights one of the most successful cases of classical biological control against a forest pest.