The violet click beetle (Limoniscus violaceus) is an endangered beetle that is protected in Europe. Its conservation required better knowledge on its biology. Recently, a study revealed that the probability of occurrence of L. violaceus in hollows increases with increasing tree circumference at 30 cm above ground and with increasing hollow decay stage (Gouix et al., submitted). However, the model showed that it was easier to identify unoccupied hollows than to identify the occupied ones. As tree hollows harbour a ränge of associated and facultative species living within a relatively small habitat, we may suspect some species interactions (competition and/or predation) that prevent Limoniscus violaceus from occupying suitable basal hollow trees. We studied beetle and Spider assemblages emerging from 73 basal hollow trees located within a Single forest site of 3500 ha (in France). All trees were considered to be suitable for Limoniscus violaceus (i.e. trees with a circumference at 30 cm above ground greater than 235 cm and cavity at an advanced stage of decay). We used the probabilistic approach to test for statistically significant pair-wise patterns of species co-occurrence. In total, 4805 species pairs were analyzed and 9.6 % had non-random patterns. We detected very few negative co-occurrence patterns (19) compared with positive ones (444). Regarding Limoniscus violaceus, we highly linked to the presence of tree hollows in mature trees. Moreover, the interaction between saproxylic insects and hollows shows specialised interacting patterns that model the structure and stability of these saproxylic assemblages. The objective of this work is to evaluate how interacting patterns of saproxylic insect networks vary according to woodland sites. We selected three representative Mediterranean woodlands in the Park: one sclerophyllous oak woodland of Quercus rotundifolia; one mixed deciduous oak woodland of Quercus pyrenaica and Quercus faginea; and one ash riparian woodland of Fraxinus angustifolia. We considered 30, 30 and 27 tree hollows, respectively, which were covered with emergence traps. Our study lasted one year, during which traps were emptied monthly and pots were replaced. We selected Coleoptera and Syrphidae (Diptera) as study groups. They were sorted according to trophic guilds: xylophagous, saproxylophagous, saprophagous, xylomycetophagous and predators. We used Aninhado and Modular programmes to evaluate the network architecture, and bipartite for R programme to study interacting attributes in the hollow-saproxylic insect interaction in each woodland site. Saproxylic insect-hollow networks presented a significant nested pattern, which means that most of the interactions are established with the most generalist nodes/species at both trophic levels (in this case, the lower trophic level is composed of hollows and the higher trophic level is composed of insects). Not all studied forests showed the same level of connectance (proportion of possible links between trees and species), the deciduous oak woodland being the forest with the most densely interconnected network
