Electrophysiological and behavioral responses of blister beetle Mylabris pustulata to plant volatiles

Plant volatiles, constitutive or induced, are perceived by insect pests to locate the host plant and also by natural enemies to locate the host insect. These plant volatiles can be utilized to develop attractive or repellant lures for pest management. Studies were carried out to identify the plant volatiles which are induced in pigeonpea, Cajanus cajan (L.) Huth due to the herbivory of blister beetle, Mylabris pustulata. The volatiles from healthy uninfested pigeonpea plants and blister beetle-infested plants were collected using the dynamic headspace collection method with Porapaq Q (80-100 mesh) as adsorbent. Using gas chromatography-mass spectrometry, 28 compounds were identified from uninfested pigeonpea plants whereas 16 compounds were identified from infested plants. A qualitative analysis showed that α-pinene and 3-hexen-2-one were exclusively detected in infested plants and (Z)-3-hexen-1-yl acetate and acetophenone were released in higher quantities from infested plants than from uninfested one. Electrophysiological evaluation of these volatiles along with other plant volatiles showed that blister beetle antennae eliciting higher responses to eucalyptol at a 1-μg dose, to nerol at a 10-μg dose and to benzyl acetate at 100- and 1000-μg doses. Beetle traps with lures of eucalyptol, benzaldehyde, benzyl acetate, and nerol attracted a very small number of blister beetle adults, suggesting the need for further efforts to standardize lure load and trap design.