Electrophysiological and behavioral responses of cabbage aphid (Brevicoryne brassicae) to rosemary (Rosmarinus officinalis) volatiles, a potential push plant for vegetable push-pull cropping system

Abstract

Abstract The cabbage aphid (Brevicoryne brassicae) is a major pest of kale (Brassica oleraceae var. acephala), an important vegetable that is grown worldwide due to its high nutritional and economic value. Brevicoryne brassicae poses a great challenge to B. oleraceae var. acephala production, causing significant direct and indirect yield losses. Farmers overly rely on synthetic insecticides to manage the pest with limited success owing to its high reproductive behavior and development of resistance. This necessitates search for sustainable alternatives to mitigate these challenges. This study assessed behavioral responses of B. brassicae to odors from rosemary (Rosmarinus officinalis) and B. oleraceae var. acephala headspace volatiles in a Perspex four-arm olfactometer. We identified and quantified volatiles emitted by each of the two plants and those eliciting behavioral response using coupled gas chromatography-mass spectrometry (GC-MS) and gas chromatography-electroantennogram (GC-EAG), respectively. Our findings revealed that B. brassicae spent more time in the arms of the olfactometer that contained B. oleraceae var. acephala volatiles compared to the arm that held R. officinalis volatiles. GC-MS analysis revealed diverse and higher quantities of volatile compounds in R. officinalis compared to B. oleraceae var. acephala. GC-EAG showed that B. brassicae was responsive to linalool, camphor, borneol, α-terpineol, verbenone, geraniol and bornyl acetate from R. officinalis and sabinene, γ-terpinene, and β-caryophyllene from B. oleraceae var. acephala. Our findings demonstrate that R. officinalis is repellent against B. brassicae and could be utilized as a ‘push’ plant in an intercropping strategy against this pest.