The essential oil (EO) from different genotypes of Lippia gracilis Schauer (Verbenaceae) present two distinctive chemotypes containing either thymol or its isomer carvacrol as major compounds, both of which have proven bioactivity against several agricultural pests. Recently, we have shown that L. gracilis accession LGRA 106 and its major compound thymol are toxic and repellent against the coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), a key pest of coconut plantations in Asia, Africa and America. Since intraspecific variation affects the chemical composition of EO and hence, its bioactivity, here we assessed the acaricidal and repellent effects of L. gracilis accession LGRA109 to A. guerreronis. Leaves of this accession contain carvacrol (49.35%) as major compound. The LC 50 of the EO and of carvacrol estimated for A. guerreronis were 28.01 and 6.84 mg/mL, respectively. Carvacrol, at its LC 50, as well as the EO and carvacrol at their LC 99, repelled the mite. Our results indicated that carvacrol and the EO of L. gracilis accession LGRA109 were bioactive against A. guerreronis; however, the EO was less effective than its major compound.
The aim of this study was to evaluate whether volatile compounds released by melon genotypes interfere in the attractiveness and repellency of Liriomyza sativae Blanchard (Diptera: Agromyzidae), and to characterise the phenolic compounds of melon genotypes, as well as the antibiotic action of these compounds on L. sativae. Through experiments, it was shown that the volatiles of the melon genotypes CNPH 06-1047-343, CNPH 06-1047-333 and CNPH 06-1047-341 showed little attractiveness to L. sativae, while the volatiles of the Goldex commercial hybrid were more attractive. By analysing the volatile profiles, it was possible to identify the compounds acetic acid, (Z)-3-hexen-1-ol, α-pinene, (Z)-β-ocimene, (E)-β-ocimene, linalool, allo-ocimene and neo-allo-ocimene. The CNPH 06-1047-343, CNPH 06-1047-333 and CNPH 06-1047-341 melon genotypes show resistant characteristics due to the non-preference of L. sativae because of the smaller number of volatiles and the higher concentration of acetic acid in their volatile composition. The phenolic compounds characterised were hydroxybenzoic-hexoside acid, ferulic acid and trihydroxy-octadecadienoic acid. The CNPH 06-1047-333 and CNPH 06-1047-341 melon genotypes presented, respectively, the highest and lowest levels of total phenolics, but there was no difference in the larval or pupal viability of L. sativae, indicating a lack of any relationship between total phenols and antibiotic resistance of the melon genotypes to L. sativae. In general, based on the analysis of volatile and phenolic compounds, the CNPH 06-1047-343, CNPH 06-1047-333 and CNPH 06-1047-341 genotypes are less attractive to L. sativae than the commercial hybrid genotypes (Goldex).
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