Chemical Composition and Insecticidal Activities of Essential Oils against the Pulse Beetle

Pulse beetles, Callosobruchus chinensis and Callosobruchus maculatus, are essential pests of cowpea, gram, soybean and pulses. Application of synthetic insecticides against the pulse beetle has led to insect resistance; insecticide residues on grains affect human health and the environment. Essential oils (EOs) are the best alternatives to synthetics due to their safety to the environment and health. The main objective of the investigation was to study the chemical composition and insecticidal activities of EOs, their combinations and compounds against the pulse beetle under laboratory. Neo-isomenthol, carvone and β-ocimene are the significant components of tested oils using GC-MS. Mentha spicata showed promising fumigant toxicity against C. chinensis (LC(50) = 0.94 µL/mL) and was followed by M. piperita (LC(50) = 0.98 µL/mL), whereas M. piperita (LC(50) = 0.92 µL/mL) against C. maculatus. A combination of Tagetes minuta + M. piperita showed more toxicity against C. chinensis after 48 h (LC(50) = 0.87 µL/mL) than T. minuta + M. spicata (LC(50) = 1.07 µL/mL). L-Carvone showed fumigant toxicity against C. chinensis after 48 h (LC(50) = 1.19 µL/mL). Binary mixtures of T. minuta +M. piperita and M. spicata showed promising toxicity and synergistic activity. EOs also exhibited repellence and ovipositional inhibition. The application of M. piperita can be recommended for the control of the pulse beetle.