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Using Candida tenuis, a yeast isolated from the digestive tube of the larva of Phoracantha semipunctata (Cerambycidae, Coleoptera), we were able to demonstrate the bioconversion of citronellal to citronellol. Response surface methodology was used to achieve the optimization of the experimental conditions for that bioconversion process. To study the proposed second-order polynomial model, we used a central composite experimental design with multiple linear regression to estimate the model coefficients of the five selected factors believed to influence the bioconversion process. Only four were demonstrated to be predominant: the incubation pH, temperature, time, and the amount of substrate. The best reduction yields (close to 90%) were obtained with alkaline pH conditions (pH 7.5), a low temperature (25°C), a small amount of substrate (15 ,ll), and short incubation time (16 h). This methodology was very efficient: only 36 experiments were necessary to assess these conditions, and model adequacy was very

Nine Scolytidae (Cryphalus piceae, Cryphalus abietis, Pityokteines curvidens, Dendroctonus micans, Ips sexdentatus, Ips typographus,Orthotomicus erosus, Tomicus piniperda, andPhloeosinus bicolor) were subjected to olfaction tests on ten conifer species taken two by two. These conifers wereAbies cephalonica, Abies nordmanniana, Picea abies, Picea orientalis, Pinus pinaster, Pinus sylvestris, Pinus brutia, Pinus laricio,Cupressus atlantica, andCupressus sempervirens. A statistical study of the results, by means of the factorial analysis of correspondence completed by the duo preference test, commonly used in sensory analysis, revealed a taxonomic clustering by genus of the plant species and analogous specific attraction behavior for the insects.Pityokteines curvidens has a behavior analogous to that of the twoCryphalus considered.Phloesinus bicolor shows a very strong specificity forCupressus. The essential oils of the conifers were analyzed to determine their terpene composition and the ten odor spectra thus obtained were compared. The hierarchical classification, using a Euclidian distance, brought out similarities in the spectra, especially in the case ofPinus. It is shown that definitive establishment of Scolytidae is not due to the presence in the odor spectrum of any particular terpenoid. The attractive power of a species results from the synergism of the different terpenes. Moreover the definitive establishment of the insects also depends on their sensorial adaptation to volatile substances which can be wider or narrower for the species studied.