Oak open woodlands are widespread in southwestern Iberia and present outstanding ecological, biodiversity and socio-economic values. Evergreen species (holm and cork oaks) are prevalent but deciduous oaks may be also locally important. Three large xylophagous cerambycids are associated to these oaks, Cerambyx welensii (Cw), C. cerdo (Cc) and Prinobius myardi (Pm). Like other saproxylic insects, these cerambycids are essential to the nutrient cycle, wood degradation and tree hollow formation, significantly contributing to biodiversity in oak forests. These cerambycids may also potentially colonise healthy living trees and become harmful or pest species. Factors driving their larval ecology are almost unknown, especially in oak forests harbouring mixed populations living in sympatry. Wood samples (n = 500 bolts) from 348 colonised trees were examined during 2011–2016 across the Extremadura region (41,634 km2). Bolts were measured, scored into five wood quality classes, dissected, and all target cerambycids were collected, measured, reared and taxonomically identified. We then determined species-specific prevalence, niche breadth, niche overlap, age structure and population density depending on wood quality, host preference, tree part, wood size, altitude and sun exposure. Wood quality and host preference were major factors segregating interspecific resource partitioning. Cw was prevalent on cork oak decayed wood, and Pm on holm oak degraded wood. Host tree part was involved in Cerambyx larval niche segregation, with Cw prevalent in the fork/branches and Cc in the trunk/base. Pm was never found inhabiting deciduous oaks. Our results may be useful to improve sustainable forest management practices in Iberian oak open woodlands.
