Host plant specificity and multi-level infestation patterns of scale insects in semi-arid forests of North Africa.

Scale insects (Hemiptera: Coccomorpha) are important sap-feeding herbivores that influence plant physiology and contribute to forest ecosystem functioning. Despite their ecological importance, their host specificity and infestation dynamics remain insufficiently documented in Mediterranean semi-arid forests. This study investigated the distribution and ecological specialization of scale insects in Belezma National Park (Algeria), focusing on host tree species, plant communities, and infested plant parts. Significant variations (p = 0.006) in infestation rates were observed among host tree species. Pinus halepensis exhibited the highest mean infestation level (58.0 ± 27.7%), followed by Juniperus phoenicea (33.0 ± 29.9%) and Juniperus oxycedrus (29.5 ± 27.4%), whereas Olea europaea (6.3 ± 2.5%) and Pistacia lentiscus (10.0 ± 8.7%) showed low susceptibility. Hierarchical analyses revealed significant associations between scale insect species and plant communities (p < 0.001). Carulaspis atlantica (Diaspididae) and Quernaspis lepineyi (Diaspididae) were associated with specific plant communities, whereas Cupressaspis mediterranea (Diaspididae) and Lineaspis striata (Diaspididae) were associated with conifer-dominated communities. At the host level, species-specific associations, such as Leucaspis pusilla (Diaspididae) with Pinus halepensis and Quernaspis lepineyi (Diaspididae) with Quercus ilex, indicated host-plant specificity. Infestation also varied among plant parts, with leaves and fruits representing the most frequently colonized structures. These findings demonstrate that scale insect distribution is primarily driven by biotic factors, particularly host plant identity and plant community. The coexistence of specialist and generalist species highlights substantial ecological plasticity and provides important insights for biodiversity conservation and sustainable forest management in Mediterranean ecosystems.