L.G. Moraal

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 Qualitative and quantitative data on O. brumata outbreaks were obtained from published sources and previously unpublished material provided by authors of this article.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.

Studies on the efficacy of the sex attractant of Paranthrene tabaniformis Rott. (Lep., Sesiidae)

The sex attractant of the poplar clearwing moth, Paranthrene tabaniformis Rott. (Lep., Sesiidae) was applied during 3 years in ‘lure and kill’ and ‘mass trapping’ experiments to prevent infestations in young poplar plantations. Although the number of males was reduced, there was no statistically significant decrease in infestations by comparison with untreated plots. The sex attractant was also used to study the moths flight behaviour. In poplar stands with trees about 15 m tall, the numbers of males captured, increased with increasing height of the traps. In young plantations, most (90 %) males fly at lower levels, up to 3.0 m, roaming along the tops of trees and other vegetation.

Artificial rearing of the poplar clearwing moth, Paranthrene tabaniformis

The poplar clearwing moth, Paranthrene tabaniformis Rott. (Lepidoptera: Sesiidae) was successfully reared through two generations on a semi‐artificial diet. Because of the long period required for larval development, three diets were used in a labour‐extensive method. The mean times required for rearing the first and second generations to adulthood on the most suitable diet averaged about 352 and 250 days, respectively. The survival to the adult stage was 6.8% for the first generation and 43.5% for the second. Biological data on sex ratio, longevity and number of eggs per female are given for adults obtained from the wild.

The effect of the game deterrent Wöbra on attacks by the poplar clearwing moth,Paranthrene tabaniformis Rott. (Lep., Sesiidae)

The game deterrent “Wöbra”, a copolymer containing quartz sand, is smeared on trees to deter mammals from damaging the bark. An experiment showed that Wöbra might act as a physical barrier against woodboring insects but it did not prevent infestations by larvae ofParanthrene tabaniformis (Lep.; Sesiidae) in one-year-old poplars. Wöbra had not adversely affected the annual height increment of the treated trees up to three years after application.ZusammenfassungDas Wildabwehrmittel „Wöbra”, ein Quarzsand enthaltendes Copolymer, wird an Baumrinden geschmiert, um Säugetiere vom Verzehr der Rinden abzuschrecken. Ein Experiment zeigte, daß Wöbra zwar als physikalische Barriere auch gegen holzbohrende Insekten dienen kann, daß es jedoch nicht bei einjährigen Pappeln gegen die Raupen des PappelglasflüglersParanthrene tabaniformis wirksam war. Auf den Höhenzuwachs der Bäume zeigte Wöbra innerhalb von 3 Jahren nach Applikation keine beeinträchtigende Wirkung.