Abstract
The coconut mite, Aceria guerreronis Keifer (Acari: Eriophyidae), is a major pest of coconut plantations (Cocos nucifera L.) worldwide. Here, we conducted a bioguided phytochemical approach using toxicity and repellency bioassays of nonpolar extract and its fractions of Vitex gardneriana Schauer (Lamiaceae) leaves to this pest. Nonpolar crude extract was fractionated by column chromatography using solvents with increased polarity and binary mixtures, resulting in five semipurified groups. The biomonitoring bioassay provided active fractions and led to the isolation and characterization of the bioactive compound squalene, a biosynthetic precursor of 20-hydroxyecdysone, which plays an important role in plant defense against arthropods. The LC50 of the crude extract of V. gardneriana for A. guerreronis was estimated to be 0.185 mg·mL-1 and LC80 = 4.123 mg·mL-1. Also, the extract was highly repellent to this pest for up to 24 h. The fractions of V. gardneriana, and also squalene, caused mortality to A. guerreronis. The potential of V. gardneriana fractions/squalene as biopesticides for controlling A. guerreronis in coconut plantations is discussed herein.
Highlights
The Lamiaceae family constitutes taxa composed of about 236 genera and around 7000 plant species widely distributed worldwide [1] [2] [3]
The biomonitoring bioassay provided active fractions and led to the isolation and characterization of the bioactive compound squalene, a biosynthetic precursor of 20-hydroxyecdysone, which plays an important role in plant defense against arthropods
The 1H Nuclear magnetic resonance (NMR) proton spectrum (600 MHz, CDCl3) showed the presence of five signals: δH 1.28 singlet attributed to methylenic groups; δH 1.63 singlet associated with water present in the deuterated chloroform solvent; δH 1.70 singlet attributed to methyl hydrogens linked to olefinic carbons; δH 1.98 - 2.07 multiplet associated with methylene hydrogens linked to olefinic carbons; and δH 5.10 - 5.20 multiplet associated with the presence of olefinic hydrogens
Summary
The Lamiaceae family constitutes taxa composed of about 236 genera and around 7000 plant species widely distributed worldwide [1] [2] [3] Species of this family are known for their medicinal and insecticidal properties, serving as raw material for the pharmaceutical and agrochemical industry [3] [4] [5]. The bracts act as physical barriers against acaricide spraying [17] [19] The attack of this pest leads to premature fruit drop, reduced fruit size, weight and water volume. Aesthetic skin necrosis reduces the value of fruits intended for the fresh market [12] [19]
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