Similarly, Floater and Zalucki (2000) found that taller trees were more easily located by the processionary caterpillar Ochrogaster lunifer. Plant odors also play an important role in host recognition and location by insects ( Visser, 1986, Bruce et al., 2005 and Tasin et al., 2006), but are more likely to be used over long distances, for the identification of suitable habitats ( Zhang and Schlyter, 2003), or to distinguish between host and non-host plants in mixed patches of vegetation with high levels of diversity. The presence of non-host trees, such as birch, has been shown to disrupt pine recognition by PPM, due to the release of non-host volatile compounds ( Jactel et al., 2011). We hypothesize
that the probability of a tree being attacked, for a given local PPM density, Lumacaftor depends primarily on two key features related to different spatial scales: (H1) host density at the stand scale, with a higher probability of attack in older stands in which tree density is lower, Selleck Dabrafenib and (H2) tree proximity to edge and host
apparency, where proximity to edge might reflect either random choice from imagos emerging from the soil outside pine stands (H2.1), a better survival of eggs and larvae at the edges because of higher temperatures (H2.2), or active PPM female choice for more apparent trees (H2.3). We tested these hypotheses by determining the percentage and distribution of the trees attacked by PPM in 145 stands of the largest pine plantation in Europe during a period between outbreaks. To investigate the mechanisms underlying PPM winter nests distribution, we experimentally tested whether the mortality rate of PPM egg batches differed according to their location within pine stands. The study was carried out in the Landes de Gascogne forest, in South West France. This region is dominated by 800,000 hectares of single species plantations of maritime pine (Pinus pinaster), of
similar age. We used and re-analyzed two datasets Sucrase described in detail by Samalens, 2009 and Castagneyrol et al., 2014, an overview of which are provided below. The first dataset was used to study the effects of host density (H1), tree distance to stand edge and host apparency (H2.1 vs. H2.3) on PPM infestation, whereas the second dataset was used to test the effect of temperature on egg survival (H2.2). Data for PPM infestations were collected in 2005 from 145 pure stands of maritime pine (P.pinaster) sampled along a systematic grid of 2 km near Pontenx-Les-Forges (44°14′N, 00°07′W) and covering a 16 × 16 km area (i.e. 25,000 ha) in the heart of the Forêt des Landes de Gascogne ( Fig. 1A). The aspect (i.e. North [N], North-East [NE], East [E], South-East [SE], South [S], South-West [SW], West [W], or North-West [NE]) of the sampled edge was recorded. Stands were between four and 61 years old and their density ranged from 113 to 2500 trees/ha.