Long‐distance dispersal and human population density allow the prediction of invasive patterns in the horse chestnut leafminerCameraria ohridella

Abstract

Summary 1.After its initial discovery in Macedonia in 1985, during the last 19 years the leafminer moth Cameraria ohridella has invaded most of Central and Western Europe. The species, which causes aesthetic damage to horse chestnuts, is generally observed first in highly populated locations before colonizing the countryside. This pattern is consistent with a stratified dispersal process combining long-distance movements and local diffusion. 2. Using large-scale spatial data on damage caused by Cameraria ohridella in Germany, three stochastic spatial models of spread are compared: a diffusion model, a leptokurtic dispersal model and a stratified dispersal model that assumes a two-scale dispersal process. In addition, the association between human population and moth invasion is tested in this last model by linking long-distance infestation probability to human population density. Finally, these spatial models constructed with data from Germany are tested at the European scale and compared to historical records of first occurrence. 3. The fat-tailed dispersal kernel models (leptokurtic and stratified dispersal models) allowing for long-distance dispersal provide better predictions than the diffusion model. Among these models, the stratified dispersal model incorporating the effect of human population density provides the best description of the spread of Cameraria ohridella in Germany in predictive (lowest sum of squared errors) and qualitative (similar fractal dimension) terms. 4. The roles of short-distance and long-distance dispersal in Cameraria ohridella invasion ecology in relation to human population are discussed, together with the models' scale-dependence and limitations.

Temporal and spatial variations in the parasitoid complex of the horse chestnut leafminer during its invasion of Europe

“…This suggests that the parasitoid complex of the NW-cluster is based on the accidental introduction of the leafminer into Austria in 1989. In this region, C. ohridella established after long-distance human transport (see Gilbert et al 2004) and parasitoids from other regions could not accumulate in the course of the host's spread, as postulated in the ''geographic spread hypothesis'' (Cornell and Hawkins 1993). In addition, the short residence time strongly limited parasitoids' chances for behavioral, phenological or biological adjustment, prerequisites for the increase of parasitoid richness in the ''adjustment-hypothesis''.…”

“…Around 1993, the two waves of spread met in Croatia and southern Hungary. Maps visualizing the spread of C. ohridella are given in Š efrová and Laštůvka (2001), Tomiczek and Krehan (1998) and Gilbert et al (2004Gilbert et al ( , 2005.…”

Applying a spread model to identify the entry points from which the pine wood nematode, the vector of pine wilt disease, would spread most rapidly across Europe

“…In addition to short distance spread, pine wilt disease can also be introduced several hundred kilometres from previously infested areas through the accidental transport of infested material by man (Robinet et al 2009). Human population density was found to be a good indicator for the risk of human assisted transportation of the pine wood nematode (Robinet et al 2009) and other insect species e.g., the horse chestnut leafminer, Cameraria ohridella (Gilbert et al 2004) and the emerald ash borer, Agrilus planipennis (Muirhead et al 2006). …”

“…However, possible long distance jumps combined with short-distance movements, so-called stratified dispersal, can significantly increase the speed of expansion (Shigesada and Kawasaki 1997;Liebhold and Tobin 2008). Increasingly, studies have shown that human-mediated dispersal plays an important role in the long-distance dispersal of invasive terrestrial invertebrates (e.g., Gilbert et al 2004;Muirhead et al 2006;Lippitt et al 2008;Pitt et al 2009;Robinet et al 2009). Since these long-distance jumps have a low probability of occurrence and are difficult to predict, the most appropriate models to describe this type of spread are stochastic although hundreds of replicate simulations may be required to obtain a representative estimate of potential spread (Pitt et al 2009;Robinet et al 2009).…”

Fronts, jumps and secondary introductions suggested as different invasion patterns in marine species, with an increase in spread rates over time

“…The front may be a continuous feature, with most suitable sites behind the front occupied, or the front may be a more diffuse feature with outlying colonies established by rarer long-distance dispersal events. Such variability in invasion pattern can be generated with different dispersal kernels, as shown when comparing the spread patterns produced under diffusion, leptokurtic and stratified diffusion models (Gilbert et al 2004). A view of invasion patterns as the consequence of an often unknown dispersal kernel may, however, underestimate the importance of other processes at a regional scale.…”