Abstract:  【Aim】To clarify the effects of low concentrations of imidacloprid on the olfactory behavior of Hippodamia variegata adults. 【Methods】The behavioral responses of H. variegata adults to healthy cotton plants and adult Aphis gossypii-infested cotton plants after ingestion of low concentrations (LC₂₀ and LC₅₀) of imidacloprid were evaluated by a Y-olfactometer, while the volatiles from healthy and adult A. gossypii-infested cotton plants were collected separately by solid-phase microextraction and analyzed by gas chromatography-mass spectrometer to identify the volatile components. In addition, the response of H. variegata adults to each volatile component was further tested. 【Results】In the absence of imidacloprid ingestion, H. variegata adults showed a significant positive preference for adult A. gossypii-infested cotton plants, but had no significant tendency to healthy cotton plants or clean air. Besides, H. variegata adults that ingested imidacloprid at low concentrations had no significant tendency to adult A. gossypii-infested cotton plants, healthy cotton plants, or clean air. We identified eight significantly increased volatile compounds from the volatiles of adult A. gossypii-infested cotton plants compared with healthy cotton plants, including myrcene, limonene, 1-decyne, 3-carene, (3E)-4, 8-dimethyl-1, 3, 7-nonatriene (DMNT), β-caryophyllene, α-humulene and (3E,7E)-4, 8, 12-trimethyltrideca-1, 3, 7, 11-tetraene (TMTT). The olfactory selection behavior of H. variegata adults to the above eight compounds measured with Y-olfactometer illustrated that H. variegata adults without imidacloprid ingestion had a significant positive tendency towards TMTT and no significant tendency to the other seven volatile compounds, while H. variegata adults that ingested imidacloprid at low concentrations had no significant positive preference for any of the eight volatile compounds. In the behavioral selection tests, the numbers of unselected individuals in H. variegata adults treated with low concentrations of imidacloprid to both volatiles from cotton plants and their single components were significantly higher than that of the control.【Conclusion】 Our results revealed that low concentrations of imidacloprid weakened the olfactory recognition of cotton plant volatiles by adult H. variegata, providing a scientific basis for the conservation and utilization of H. variegata and the rational use of pesticides in Xinjiang cotton fields.

Key words: Hippodamia variegata, imidacloprid, olfactory selection behavior, volatile, sublethal effects