The flathead oak borer (Coroebus undatus [= Coraebus undatus]) is a beetle of the Buprestidae family that, in the larva stage, lives under the bark of the cork oak, in the germ layer called cambium that produces wood towards the interior and bark –in this case cork- outwards.
In its larval stage, the flathead oak borer is one white worm 20 – 50 mm length. It spends 2 years in the larval stage mining the cambium and the cork. Once its larval period ends, it opens a gallery in the cork towards the outside where it will go to the pupal stage. Finally, in June or July, it will finish the gallery and emerge as adult leaving a hole in the trunk. The adult is a typical Buprestidae of stake shape, wider in the head and shoulder than in the abdomen. The adult of flathead oak borer is 10 to 14 mm in length. The head, the pronotum and the front half of the elytra are shiny tan or gold that discolor to black in the caudal half. In this black caudal half of the elytra there are 3 sinuous white stripes, the last one not as wavy as the remaining two.
The flathead oak borer damages significantly the quality and value of the cork. The mined by the galleries of the flathead oak borer cork can not be used to make caps, they won’t seal. The presence of bores in the cork still in the oak is revealed by white stains caused by spilled sap that outstand on the mahogany color provided the cork was already removed years ago.
The flathead oak borer is fought with pheromone traps to attract males in June and July and through meshes placed on the trunk of the cork oak to capture the adults that may emerge from it. Due to its negative impact on cork production, flathead oak borer has been studied mainly by forestry engineers from agricultural and forestry institutes and administrations.
The flathead oak borer does not affect only the cork oak (Quercus suber), although the cork oak is its main victim. In the district of Bages, where there are no cork oaks, the flathead oak borer is found in holm oak (Quercus ilex), although infections are smaller. The flathead oak borer in the holm oak is neglected since its bark does not have any prominent use. The individual of the image was photographed in a holm oak forest in the range of Montserrat.
In addition to Coroebus undatus, the flathead oak borer of the cork, there is C. florentinus, the flathead oak borer of the branchs, similar, whose larvae live and dry small branches of cork and holm oaks.
[photo Jordi Badia]