Evaluation of fumigant toxicity and behavioral effect of mint and rosemary essential oils in the cowpea weevil

The cowpea weevil is one of the most important pests of legumes in the farm and warehouse, which causes a lot of damage. Plant essential oils are an excellent alternative to many pesticides to control pests. In this study, the behavioral response of newly emerged cowpea weevil was compared against the fumigant toxicity of two essential oils of mint and rosemary, and then the differences in their mode of action were examined according to the constituents. Insects behavioral changes under the influence of essential oil treatment were investigated, and the mortality of insects was recorded up to 24 hours after treatment, every two hours, without opening the Petri dish lid. The results showed that the toxicity of both essential oils was statistically similar, but the type of insect behavior before death was different in the mint and rosemary essential oils. Unlike the mint essential oil, insects exposed to rosemary essential oil showed signs of overstimulation, the opening of the upper and lower wings, tremors, and death-related seizures. According to the research results, both essential oils had strong insecticidal properties on the cowpea weevil, but according to the symptoms of death, it seems that rosemary essential oil can affect GABAergic receptors on the one hand and acetylcholinesterase enzyme inhibition on the other hand and affects the nervous system and causes insect death, but under the influence of mint essential oil insect death occurred without specific symptoms, requiring further research about the mode of action of the essential oil in this insect.