Chemical composition of the headspace volatiles of intact cowpea pods and cowpea pods infested by Riptortus dentipes and Nezara viridula pests

Abstract

Volatile organic compounds are released by plants in defense against herbivory feeding by insect pests. Pod-sucking bugs can cause 30–70 % yield losses in cowpea (Vigna unguiculata) which serves as a major source of rich proteins and vitamins for humans and animals, as well as a source of income for farmers. The purpose of this study was to determine the chemical composition of the headspace volatiles of intact cowpea pods (Vigna unguiculata) variety (Padituya), and when it is infested by two pod-sucking bugs Riptortus dentipes and Nezara viridula. Headspace volatile collection was employed to collect volatile organic compounds from the intact cowpea pods, cowpea pods infested with Riptortus dentipes, and cowpea pods infested with Nezara viridula. Entrainment was done for 96 h in each case. The entrained volatiles were analyzed by gas chromatograph coupled with a mass spectrometer (GC-MS). Analysis of GC-MS data led to the identification of 1-octen-3-ol, 3-octanol, 2-nonanone, oleic acid, octadecanoic acid and dodecanoic acid as the volatiles released by the cowpea pod without insect attack. Cowpea pods attacked by Riptortus dentipes released hexanoic acid, 3-hexenoic acid (E), hexanoic acid, 2-hexenyl hexanoate (E), 2-tridecanone, 1-(4-ethylphenyl)-ethanone and eicosanoic acid. Upon infestation with Nezara viridula, the pods released 2-pentanone, 4-hydroxy-4-methyl-, 3-ethylbenzaldehyde, 1-(4-ethylphenyl)-ethanone and 2-decenyl acetate (E). With the exception of 1-(4-ethylphenyl)-ethanone, different volatile organic compounds were released by the cowpea plant against the two pests upon infestation. These compounds could be synthesized and used in integrated pest management of these pests to reduce losses in yield of cowpea production.