Site condition and predation influence a bark beetle's success: a spatially realistic approach

Abstract

1 Spatial pattern in abundance of Dendroctonus micans was studied in a 600-ha spruce stand in the Massif Central (LozeÁ re, France). The proportion of trees attacked was measured in 38 plots and these data were used to estimate spatial pattern of attack density in the stand and to identify a transect of decreasing attack density (80% to 30%) over less than 1000 m. 2 Spatial variation in attack density was analysed in relation to (i) data on site and stand characteristics (altitude, slope, tree density, tree average height, yield class and average age) collected from 63 points in the stand and (ii) the releases of the predator Rhizophagus grandis (localization and number of beetles released). 3 The proportion of attacked trees was analysed using geostatistics and showed a strong spatial structure reflecting the spatial scale of interaction of D. micans with its environment. The spatial structure was modelled in order to estimate the spatial distribution of attack density at unsampled locations. 4 A linear model relating interpolated attack density to the number of predators released 6±10 years before the survey in a 300-m radius and to the average slope over a 250-m radius explained 67% of the observed variability. Spatial autocorrelation was taken into account in a spatial regression model.

Terrestrial insects along elevation gradients: species and community responses to altitude

“…Equivalent examples of species replacement along altitudinal gradients are found among such diverse groups as grassland bugs (Auchenorrhyncha) and dung-feeding flies (Sepsidae) in northern England (Randall et al, 1981 ;Eyre, Woodward & Luff, 2001), horseflies and grasshoppers in the French mountains (Claridge & Singrao, 1978;Raymond, 1979) and satyrid butterflies in Venezuela (Adams & Bernard, 1981). Gilbert & Gregoire (2003) The availability of particular host plant species to a particular set of related insect species can also change with altitude, as in the bruchid beetle Bruchidius complex feeding on Acacia species in Saudi Arabia (Abdullah & Abulfatih, 1995). In this situation the relative performance of insect species is likely to vary between different host plants, potentially shifting the competitive balance between the insect species present at any particular altitude.…”

Multiscale spatial variation of the bark beetle Ips sexdentatus damage in a pine plantation forest (Landes de Gascogne, Southwestern France)

“…Their distribution therefore reflects management options and landscape structure and may dramatically affect the spatial pattern of bark beetles populations. Although the mechanisms by which bark beetles colonize individual living trees are well understood there is still a limited amount of spatially explicit information on the pattern of attacks and most notably studies at the landscape scale are lacking (but see Coulson et al, 1999;Gilbert et al, 2005;Gilbert and Gré goire, 2003).…”

Spatial pattern of invading Dendroctonus micans (Coleoptera: Scolytidae) populations in the United Kingdom

“…Short-distance stand-to-stand dispersal in D. micans is probably accomplished mainly by flight of individual adults. Flight ability is assumed to be quite high (over 10 km in good climatic conditions ;Forsse 1989), but this flight distance may be significantly lower where host trees are abundant (Gilbert and Grégoire 2003). Thus D. micans can be assumed to present "stratified dispersal" (Hengeveld 1989;Shigesada and Kawasaki 1997), which combines longdistance "jump spread" performed by passive transportation, with local population movements ("smooth spread") carried out by flight.…”