Essential oils, which are mixtures of terpenes, frequently show stronger insecticide activity, i.e., lower lethal dose 50 (LC50), than their most abundant terpenes. Synergy between terpenes provides a plausible explanation, but its demonstration has been elusive. In the present work, we look for an alternative explanation, by considering the influence of insect metabolic detoxification. Basically, we propose a model (metabolic model, MM) in which the LC50 of the major terpene in a mixture is expected to include a fraction that is detoxified by the insect, whereas a minor terpene would act unimpeded, showing a lower LC50 than when acting alone. In order to test this idea, we analyzed the effects of inhibiting the cytochrome P450 detoxification system with piperonyl butoxide (PBO), on the lethal concentration of terpenes as fumigants against Musca domestica. We found that, within a group of 10 terpenes [linalool, citronellal, (R)-α-pinene, 1,8-cineole, γ-terpinene, limonene, α-terpinene, (S)-β-pinene, thymol and (R)-pulegone], seven showed the LC50PBO (the lethal concentration for PBO-treated flies) between 1.7 and 12.4 times lower than the corresponding LC50 when P450 was not inhibited. Only in one case, that of (R)-pulegone, was the LC50PBO greater than the LC50, while two terpenes [(S)-β-pinene and thymol] showed no changes in toxicity. The increased activity of most terpenes (particularly linalool and citronellal) in PBO-treated flies supports our hypothesis that normally the LC50 includes a fraction of inactive compound, due to detoxification. Having previously determined that M. domestica preferentially oxidizes the most abundant terpene in a mixture, while terpenes in smaller proportions are poorly or not detoxified by the P450 system, we assessed whether the toxicity of minority terpenes in a mixture is similar to their activity under P450 inhibition. We chose suitable binary combinations in such a way that one terpene (in greater proportion) should be the target of P450 while the other (in smaller proportion) should intoxicate the fly with LC50PBO or similar. Combinations of 1,8-cineole-citronellal, 1,8-cineole-linalool, linalool-citronellal, (R)-pulegone-linalool, (R)-pulegone-1,8-cineole and (R)-pulegone-citronellal were assayed against M. domestica, and the LC50 of each mixture was determined and compared to values predicted by MM (considering the LC50PBO for minor component) or by the classical approach (LC50 for both components). The MM showed the best fit to the data, suggesting additive rather than synergistic effects, except for the combination of (R)-pulegone-citronellal that was clearly synergistic. Thus, the experimental data indicate that the insect preferentially oxidizes the major component in a mixture, while the terpene in lesser proportion acts as a toxicant, with higher toxicity than when it was assayed alone. These findings contribute to a deeper understanding of the higher toxicity of essential oils compared to their component terpenes and provide important information for the design of...

The purpose of this research study was to examine the rater reliability and the concurrent validity of the Language Center oral assessment rubric (LCR) with the KET (Key English Test) and PET (Preliminary English Test), Cambridge Examinations. Thirty two students from beginning and intermediate levels participated in the study. Validity estimations included both logical and empirical analyses. Results from logical analyses indicated that the rubric has construct validity. Empirical analyses were conducted by establishing patterns of correlations between the two sets of measures. Results showed low correlations between KET and LCR and from moderate to strong among LCR evaluators. Further, strong correlations between PET and LCR were found suggesting that both measure a similar construct. The results indicate the need to adjust the rubric to low level students and to develop teacher education programs where training toward consistency in evaluation will br conducted.

Frustrations with traditional testing led a group of teachers at the English for adults program at Universidad eafit (Colombia) to design tests aligned with the institutional teaching philosophy and classroom practices. This article reports on a study of an item-by-item evaluation of a series of English exams for validity and reliability in an effort to guarantee the quality of the process of test design. The study included descriptive statistics, item analysis, correlational analyses, reliability estimates, and validity analyses. The results show that the new tests are an excellent addition to the program and an improvement over traditional tests. Implications are discussed and recommendations given for the development of any institutional testing program.Key words: Classroom tests, integrated language skills, reliability, validity.Las frustraciones con la evaluación tradicional llevaron a un grupo de profesores del programa de inglés para adultos de la Universidad eafit (Colombia) a diseñar pruebas alineadas con la filosofía de enseñanza institucional y las prácticas de clase. Este artículo describe un estudio de validez y confiabilidad de exámenes de inglés, ítem por ítem, para garantizar la calidad del diseño de pruebas. El estudio incluyó estadística descriptiva, análisis de ítems, análisis de correlación, confiabilidad de las estimaciones y análisis de validez. Los resultados muestran que las pruebas son una excelente adición al programa con respecto a exámenes tradicionales. Igualmente se discuten las implicaciones y se hacen recomendaciones para el desarrollo de cualquier programa institucional de pruebas.Palabras clave: confiabilidad, habilidades lingüísticas integradas, pruebas, validez.