Bioactivity-guided isolation of rosmarinic acid as the principle bioactive compound from the butanol extract of Isodon rugosus against the pea aphid, Acyrthosiphon pisum.

Saira Khan,Clauvis Nji Tizi Taning,Elias Bonneure,Muhammad Asif,Guy Smagghe,Sven Mangelinckx,Raza Ahmad,Nighat Fatima,Mohammad Maroof Shah,Ahmed Ibrahim Hasaballah

doi:10.1371/journal.pone.0215048

Saira Khan, Clauvis Nji Tizi Taning + Show 8 more

Open Access

https://doi.org/10.1371/journal.pone.0215048

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Abstract

Aphids are agricultural pest insects that transmit viruses and cause feeding damage on a global scale. Current pest control practices involving the excessive use of synthetic insecticides over many years have resulted in aphid resistance to a number of pesticides. In nature, plants produce secondary metabolites during their interaction with insects and these metabolites can act as toxicants, antifeedants, anti-oviposition agents and deterrents towards the insects. In a previous study, we demonstrated that the butanol fraction from a crude methanolic extract of an important plant species, Isodon rugosus showed strong insecticidal activity against the pea aphid, Acyrthosiphon pisum. To further explore this finding, the current study aimed to exploit a bioactivity-guided strategy to isolate and identify the active compound in the butanol fraction of I. rugosus. As such, reversed-phase flash chromatography, acidic extraction and different spectroscopic techniques were used to isolate and identify the new compound, rosmarinic acid, as the bioactive compound in I. rugosus. Insecticidal potential of rosmarinic acid against A. pisum was evaluated using standard protocols and the data obtained was analyzed using qualitative and quantitative statistical approaches. Considering that a very low concentration of this compound (LC90 = 5.4 ppm) causes significant mortality in A. pisum within 24 h, rosmarinic acid could be exploited as a potent insecticide against this important pest insect. Furthermore, I. rugosus is already used for medicinal purposes and rosmarinic acid is known to reduce genotoxic effects induced by chemicals, hence it is expected to be safer compared to the current conventional pesticides. While this study highlights the potential of I. rugosus as a possible biopesticide source against A. pisum, it also provides the basis for further exploration and development of formulations for effective field application.

Highlights

Aphids are among the most important agricultural pest insects of many crops worldwide
We evaluated the aphicidal properties of the hexane, dichloromethane, butanol and ethyl acetate fractions of a crude methanolic extract from I. rugosus, and confirmed that the butanol fraction showed the best activity against the pea aphid, A. pisum [27]
Rosmarinic acid as a pesticidal compound isolated from Isodon rugosus against aphid, Acyrthosiphon pisum extraction with ethyl acetate, two phases, ethyl acetate and aqueous, were obtained

Summary

Introduction

Aphids are among the most important agricultural pest insects of many crops worldwide. They feed exclusively on plant phloem sap by inserting their needle-shaped mouthparts into sieve elements, usually resulting to plant discoloration, stunting and deformation. The pea aphid, Acyrthosiphon pisum (Hemiptera: Aphididae), adversely affects economically important legume crops worldwide. It is oligophagous, comprising of a number of biotypes or races living on a number of legume hosts (red clover, pea, broad bean and alfalfa races) [6,7,8,9]. Current aphid control strategies predominantly rely on the use of insecticides such as carbamates, organophosphates, pyrethroids, neonicotinoids and pymetrozine [10]. The repeated use of these insecticides for many years has resulted in aphid resistance to most insecticides, making it very difficult to control aphids [11]

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