Abstract:The oak decline is probably the most severe plant health problem faced in the Mediterranean region which is one of the habitats of community interest under the EU's environmental legal regime. More information on the role of Cerambycids species in this decay is still needed. This paper reports the apparent survival rate (Phi) and recapture rate (P) for a population of Cerambyx welensii Küster (Coleoptera cerambycidae) in a highly degraded cork oak grove near the Doñana National Park (Huelva, Spain) as calculated using the mark-capture-recapture method. High and constants in the time values of apparent survival rates for males and females are detected. The male overall recapture rate (P) exceeded that of the female group with relatively low, but significant, values. The presence of transient individuals suggests a nucleus of population with many immigrants and emigrants in the study plot. The results are used to discuss various aspects of the insect biology, and the potential effect of the gradual deterioration of the studied ecosystem on the insect population it supports.

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Abstract. The dehesa is a silvopastoral system of a high economic and ecological signifi cance in the Iberian Peninsula that is protected under the EEC/92/43 Habitat Directive. One of the most serious problems the dehesa system is currently facing is oak decline. This tree decay process is largely caused by three xylophagous cerambycids of which Prinobius myardi is the least known. In this study, we used a capture-mark-recapture method to identify the models best fi tting the behaviour of this species with a view to estimating basic population parameters such as survival rate (phi), recapture rate (p) and transiency index (T). Prinobius myardi adults were captured by hand following visual detection in the trees of a cork oak (Quercus suber) plot located in the close vicinity of the Doñana National Park (SW Spain). Males exhibited a constant survival rate exceeding 85.4% throughout their fl ight period, a maximum transiency index of 1.82% and a recapture rate ranging from 42.50% to 76.90%. These results are suggestive of a sedentary behaviour in P. myardi males. By contrast, the small number of females captured precluded calculation of the previous parameters for this gender; in any case, fi eld observations revealed a fl eeing, less sedentary behaviour with respect to the males.Résumé. Analyse de la dynamique de population de Prinobius myardi Mulsant dans un peuplement de chêne-liège. La dehesa est un système sylvopastoral de grande importance économique et écologique pour la Péninsule Ibérique. Elle est protégée par la directive «Habitat» EEC/9243. Un des problèmes les plus sérieux qui menace le système de la dehesa est le déclin du chêne-liège (Quercus suber). Ce processus de dégradation de cet arbre est largement dû à trois cérambycides parmi lesquels Prinobius myardi est le moins connu. Dans cette étude, nous avons utilisé une méthode de capture-marquage-recapture pour identifi er le modèle qui s'adapte le mieux au mode de vie de cette espèce. Dans ce but, on a estimé les paramètres de base comme le taux de survie (phi), le taux de recapture (p) et l'index de transition (T). Les Prinobius myardi adultes ont été capturés à la main, après une détection à vue, dans des placeaux de chêne-liège au voisinage du Parc National de la Doñana (SW Espagne). Les mâles ont présenté un taux de survie constant qui dépasse 85,4% tout au long de leur période de vol, un index de transition maximal de 1,82% et un taux de recapture de 42,5 à 76,90%. Ces résultats suggèrent un mode de vie sédentaire chez les mâles de P. myardi. Par contraste, le faible nombre de femelles capturées empèche de calcul de ces paramètres pour ce sexe. De toute façon, les observations montrent qu'elles sont moins sédentaires que les mâles au cours de leur période de vol.

& Key message Cork oaks highly infested by Cerambyx welensii emit an amount of limonene at dusk, when C. welensii adults become active. In contrast, emissions by neighboring cork oaks free of C. welensii are dominated by pinene-type compounds. & Context The activity of the woodborer Cerambyx welensii Küster is a key factor in the decline of Quercus suber L. dehesas. & Aims This study aimed to estimate whether trees highly infested by C. welensii exhibited a peculiar emission profile, with known antennally active compounds. & Methods Monoterpenes were sampled in situ in 2006 (day/late evening) and 2008 (early evening) from Q. suber stratified by whether or not trees were highly infested by C. welensii and analyzed by gas chromatography. & Results Limonene, α-pinene, β-pinene, sabinene, and myrcene accounted for over 87.2% of overall monoterpene emissions. Monoterpene composition and emission rates differed between the two groups, both during daytime and early evening, with a high presence of limonene in infested trees and dominance of pinene-type compounds in non-infested trees. & Conclusion This work evidenced differences in foliar monoterpene emissions between Q. suber trees highly infested by C. welensii and non-infested trees, with a high presence of limonene in the former and dominance of pinene-type compounds in non-infested trees. We hypothesize that the detection-especially during the onset of insects daily flight-of certain compounds (e.g., limonene), together with the detection of specific ratios of several monoterpenes (e.g., those of limonene to pinenetype compounds), has a role in the intraspecific host selection by C. welensii.

The dehesa is a traditional agrosilvopastoral ecosystem characterized by a savanna-like structure. It has been in decline since the middle of the last century, in particular in agricultural environments where it has been relegated to isolated forests. This paper presents a study into the reduction over the past 50 years. One of the main causes of this decline has been identified as xylophagous insects, specifically the wood borer Cerambyx welensii Kuster (Coleoptera: Cerambycidae). Based on estimations in both the population size, using Jolly Seber models, and the level of tree injury, using a single-index model, the study investigates the role the insect has played in the decline of the dehesa. Surface area loss was found to be greater than 50%, while canopy cover has diminished linearly over the period studied, with the risk of disappearance of the woodland increasing in the same magnitude as borer population density. The highest wood borer population densities observed corresponded to stands with an average canopy cover loss of 1.68% a year, indicating a risk of completely losing the forest cover in the short term (10–30 years). The proposed tree injury index was successful in categorizing the size of the insect population, and seems to be a useful indicator for describing the relationship between the two variables. According to this indicator, woodlands with more than 10% of trees with severe or very severe injuries are at risk. Follow-up work should be undertaken to investigate long-term demographic changes in wood borer populations, and management practices should be developed to reduce the population size, minimize forest loss and preserve these relict oak trees in unconnected landscapes.