QSAR Study of Biologically Active Essential Oils against Beetles infesting the Walnut in Catamarca, Argentine

Abstract

Repellent and contact toxicity activity of the essential oils of Laurus nobilis (Lauraceae), Lippia integrifolia (Verbenaceae), Aloysia polystachya (Verbenaceae), Tagetes minuta (Asteraceae), Pimpinella anisum (Apiaceae) and Cuminum cyminum (Apiaceae) growing in Catamarca, Argentina against weevils of the genus Carpophilus and Oryzaephilus that infesting the production of walnuts were evaluated. Yields of essential oils obtained by hydrodistillation range from 1.0 to 4 % (v/w). Analysis by gas chromatography-mass spectrometry of the EOs led the identification of their major constituents and their relative proportions. Repellence/toxicity test assayed by impregnation on filter paper discs were performed using different doses. Experimental data were analysed using Generalized Estimating Equations (GEE; IBM SPSS Statistics 23.0) with normal distribution and the identity link function. The dependent variables were the mean repellency values of 5 repetitions. Predictors entered into the model were oil treatment, employed doses, the time points and all 2-way interactions between them. The working correlation matrix was assumed to be unstructured. From the tested essential oils spectral information, we work their molecular modeling as mixtures from the development of one descriptor combining the molecular descriptors of each component in the mixture and its molar fraction , i.e. . The application of chemoinformatic approaches determined that a combination of mixture descriptors related with molecular size, branchedness, charge distribution and electronegativity is useful to explain the repellent activity profile against Carpophilus spp and Orizaephilus spp. According PCA calculations, while repellency against Carpophilus spp increase with EOs containing molecules composed of flexible substructures formed by saturate aliphatic carbon chains and a number reduced of non-hydrogen substituents, the activity profile against Orizaephilus spp appears to be favored by aliphatic hydrophobic functions linked to one hydrogen bond acceptor function. These models were validated with 9 and 4 EOs (test sets) reported with repellent activity against weevils of the Nitidulidae and Silvanidae family. Each PCA model confirm to each EOs as repellent with a comparable performance to the experimental reports.