Composition of the Essential Oil and Insecticidal Activity of Launaea taraxacifolia (Willd.) Amin ex C. Jeffrey Growing in Nigeria

Moses S Owolabi,Akintayo L Ogundajo,Kafayat O Ajelara,Azeezat O Alafia,William N Setzer

doi:10.3390/foods9070914

Moses S Owolabi, Akintayo L Ogundajo + Show 3 more

Open Access

https://doi.org/10.3390/foods9070914

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Abstract

The rice weevil (Sitophilus oryzae) is a pest of stored grain products such as rice, wheat, and corn. Essential oils represent a green environmentally-friendly alternative to synthetic pesticides for controlling stored-product insect pests. Launaea taraxacifolia is a leafy vegetable plant found in several parts of Nigeria. The leaves are eaten either fresh as a salad or cooked as a sauce. The essential oil obtained from fresh leaves of L. taraxacifolia was obtained by hydrodistillation and analyzed by gas chromatography/mass spectrometry (GC-MS). Twenty-nine compounds were identified, accounting for 100% of the oil composition. The major component classes were monoterpene hydrocarbons (78.1%), followed by oxygenated monoterpenoids (16.2%), sesquiterpene hydrocarbons (2.1%), oxygenated sesquiterpenoids (0.3%), and non-terpenoid derivatives (3.3%). The leaf essential oil was dominated by monoterpene hydrocarbons including limonene (48.8%), sabinene (18.8%), and (E)-β-ocimene (4.6%), along with the monoterpenoid aldehyde citronellal (11.0%). The contact insecticidal activity of L. taraxacifolia essential oil against Sitophilus oryzae was carried out; median lethal concentration (LC50) values of topical exposure of L. taraxacifolia essential oil were assessed over a 120-h period. The LC50 values ranged from 54.38 μL/mL (24 h) to 10.10 µL/mL (120 h). The insecticidal activity of the L. taraxacifolia essential oil can be attributed to major components limonene (48.8%), sabinene (18.8%), and citronellal (11.0%), as well as potential synergistic action of the essential oil components. This result showed L. taraxacifolia essential oil may be considered as a useful alternative to synthetic insecticides.

Highlights

Insects such as Callosobruchus maculatus (Fabr.), Sitophilus granarius (L.), S. oryzae (L.), S. zeamais (Motsch.), and Tribolium castaneum (Herbst), are important pests that attack stored grains, causing widespread economic losses [1,2,3]
The essential oil from L. taraxacifolia was obtained by hydrodistillation with a yield of 1.68% as a pale-yellow essential oil, which was analyzed by gas chromatography/mass spectrometry (GC-MS)
The leaf essential oil was dominated by monoterpene hydrocarbons including limonene (48.8%), sabinene (18.8%), and (E)-β-ocimene

Summary

Introduction

Insects such as Callosobruchus maculatus (Fabr.) (bruchid beetle), Sitophilus granarius (L.) (wheat weevil), S. oryzae (L.) (rice weevil), S. zeamais (Motsch.) (maize weevil), and Tribolium castaneum (Herbst) (red flour beetle), are important pests that attack stored grains, causing widespread economic losses [1,2,3]. The long-term use of synthetic insecticides to control these pests has become problematic, . Compounds such as chlorinated hydrocarbons, organophosphates, carbamates, etc., tend to be toxic to non-target organisms such as mammals, birds, and fish [4,5,6], they are persistent in the environment [7,8,9,10], and many stored-grain insect pests have developed insecticide resistance [11,12,13]. The present research was undertaken with the aim of investigating the essential oil composition and evaluating the insecticidal potential of L. taraxacifolia leaves from southwestern Nigeria

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