Effect of host tree density and apparency on the probability of attack by the pine processionary moth

Abstract

a b s t r a c tThe pine processionary moth (PPM, Thaumetopoea pityocampa) is the main defoliator of pines in the Mediterranean area, necessitating constant surveillance and regular pest management. A sound understanding of the spatial distribution of infested trees, both within and between stands, is required to increase management efficiency. We hypothesized that both host tree density at stand scale and tree apparency at individual tree scale were responsible for between-and within-stand patterns of PPM infestation. We tested these hypotheses on a sample of 171 maritime pine stands in the Landes de Gascogne, the largest plantation forest in Europe. We showed that PPM infestation (percentage of infested trees) decreased significantly with stand density, and was therefore greater in older than in younger stands. The probability of a pine tree being attacked increased significantly with tree height and proximity to the edge of the stand. Mortality rates of exposed sentinel egg batches did not differ with distance from the stand edge. We discuss three likely explanations for higher infestation of taller trees at stand edges: better survival of larvae on sun-exposed trees, and random interception vs. active host selection by gravid females. Our findings suggest that stand management could be adapted in order to decrease the risk of damage by the pine processionary moth, and that predictive tools for infestation dynamics can be based on forest growth models.

Individual tree traits shape insect and disease damage on oak in a climate‐matching tree diversity experiment

“…Here, we found that taller trees experienced higher herbivory and mildew, especially when growing in the context of less vigorous surrounding trees. For insect herbivores, apparency may determine host searching efficiency, as has been suggested previously for the pine processionary moth (Régolini et al, 2014). For powdery mildew, a passive, wind-dispersed pathogen (Marçais & Desprez-Loustau, 2014), spore interception may be more efficient when hosts are taller and therefore more prominent in the landscape.…”

“…Direct effects of nonhost neighbor trees may cause associational resistance by influencing the microclimate of plots with knock‐on impacts on insects (Muiruri & Koricheva, ), or by interfering with olfactory cues used by pests to find hosts (Jactel, Birgersson, Andersson, & Schlyter, ). Tree species diversity may also modify plant apparency, which can be defined the height of focal trees relative to their surroundings, and has been shown to be an important predictor of insect herbivore loads on individual trees (Castagneyrol, Giffard, Péré, & Jactel, ; Régolini et al, ). Moreover, complex indirect effects of plant neighborhood identity on insect herbivory and pathogens may be mediated via modifications to plant traits, including foliar nutritional quality and defenses against herbivory (Castagneyrol et al, ; Forey et al, ).…”

Background losses of woody plant foliage to insects show variable relationships with plant functional traits across the globe

“…; Regolini et al . ). We demonstrated that herbivory differs among woody plant life forms, generally increasing with increases in average plant height (from dwarf shrubs to shrubs and then to trees).…”

Evaluation of damage caused by Ectinogonia buquetti (Coleoptera: Buprestidae) in dendroenergetic plantations of Eucalyptus camaldulensis

“…However, Régolini et al (2014) found that there is no effect between tree density and the probability of attack of Thaumetopoea pityocampa on pure stands of Pinus pinaster between four and 61 years of age. These authors found that trees were more likely to be affected on edge plots than on inner plots, and the chance of attack increases with tree diameter; suggesting that taller trees were more likely to be attacked than smaller ones.…”

“…However, adult insects were detected at native forest fragments in ravines, using exotic plantations to feed and reproduce. According to Régolini et al (2014), it is probable that feeding resources (Eucalyptus camaldulensis trees) were abundant enough regarding Ectinogonia buquetti population, ensuring that females were able to find suitable habitats throughout the landscape. However, these assumptions could not be tested with data collected in this study, but may allow the design of future research in this area.…”