Fabrication of a vertical Y-tube olfactometer for the assessment of spatial repellency of essential oils against Helopeltis theivora waterhouse

Pesticide resistance, cross-resistance, and limitation of potential biopesticide on Helopeltis theivora Waterhouse [Commonly known as tea mosquito bug (TMB)] have strongly triggered notable economic losses in tea [Camellia sinensis (L.) O. Kuntze] industries across African and some selected Asian countries like India and Bangladesh. Repellent agents like essential oils (EOs) could be quite promising to reduce the adverse and numerous side effects of synthetic pesticides; however, scientific study on chemoreception through olfaction, as a sensory modality on this pest, is yet to be done. In this study, therefore, spatial olfactory response of few selected essential oils (N=7) has been highlighted in a modified vertical Y-tube olfactometer (VYTO), which is based on the negative geotaxis crawling movement (NGCM) of the pest within the confined environment of the olfactometer. The NGCM distance covered by the TMBs was 80 cm in 16.02 ± 1.47 (Mean ± SD) min with a speed of 8×10-3 m/s. This study is also first to report the spatial repellency, as spatial activity index (SAI), of transfluthrin as a positive control (0.88%) against TMBs [SAI of 0.849 ± 0.042 (Mean ± SD)]. Based on EOs yield, natural abundance, and growth, wild Agerartum conyzoides (L.) was found to be a potential spatial repellent agent [SAI of 0.925 ± 0.036 (Mean ± SD)] against adult female TMBs. GC-MS analysis of A. conyzoides detected precocene I and precocene II, as the most probable metabolites within the highest peak area (%). This study will definitely help in the behavioral study on TMBs in the future; especially, in the elucidation of spatial bio-insecticidal properties of the abundant volatile aromatic compounds in the natural environment.