g. on higher trees and trees located at stand edges may be explained by three main non-exclusive hypotheses. The first

one (H2.1) is that PPM female moths are rather unselective when ovipositionning as suggested by Hódar et al. (2002). As imagos usually emerge from the soil outside pine stands, female pine processionary moths find more would just by chance first encounter edge trees or be intercepted by trees with larger crown. According to this hypothesis, the within stand distribution of PPM nests may simply result from passive interception of gravid females by particular trees. Alternatively (H2.2), a better survival of eggs and larvae on taller trees or on trees located at stand edges may be expected because they would benefit from more sunshine and then higher

temperatures in winter, thus leading Roxadustat to better conditions for development (Battisti et al., 2013). The last hypothesis (H2.3) is that the probability of an individual tree being attacked by the PPM would result from an active PPM female choice for more apparent trees, either due to their location at stand edge (Dulaurent et al., 2012) or their higher height. The edge effect on PPM infestation can account to both “random interception” and “active host selection” hypotheses (H2.1) and (H2.3). Pérez-Contreras and Tierno de Figueroa (1997) showed that the number of PPM egg batches increased with pine height and was significantly different between the two pine species (Pinushalepensis and P. pinaster) in mixture. More recently Pérez-Contreras et al. (2014) showed again that, independently of the pupation site, gravid females of pine processionary moth

were able to choose for ovipositionning between two host pine species (P. halepensis and P. pinaster), even if these pine species were randomly distributed within a stand. Although these findings indicate that females can discriminate and actively select their host between two pine species, they do not bring information on female selection amongst individual pines of the same species. Therefore, despite a partial support for H2.3 (i.e. active host selection), the alternative hypothesis not (random interception H2.1) cannot be fully discarded. Further experiment should focus on female flight behavior during the oviposition period in order to arbitrate between these two hypotheses (H2.1 vs. H2.3). The main reason put forward for the lower mortality of PPM on taller trees and/or trees located at the stand edge (H2.2) is that they receive more sunshine, resulting in a more favorable microclimate for the offspring (Battisti et al., 2005, Battisti et al., 2013 and Buffo et al., 2007). PPM larvae are thought to prefer spinning their nests on parts of the tree crown exposed to sunshine, where they can absorb warmth and are likely to be more resistant to low winter temperatures (Geri, 1980, Geri, 1984 and Hoch et al., 2009). In our experiment, we found no significant difference in egg survival, in relation to distance from stand edge.