Combining essential oils and kaolin clay increased repellency against Bemisia tabaci (Hemiptera: Aleyrodidae): implications for management

The sweetpotato whitefly, Bemisia tabaci (Gennadius) (Hemiptera: Aleyrodidae), is a major pest of vegetable crops worldwide. Management of this pest relies on insecticides, but overuse has led to resistance development and negative effects on non-target organisms. Repellent essential oils can be a sustainable alternative to insecticides. The residual efficacy of essential oils is relatively short, but combining them with kaolin clay provides enhanced repellency against whiteflies and a slower release rate. While many essential oils have been evaluated against whiteflies, most studies utilize different protocols, making comparisons between compounds challenging. In this study, 12 essential oils were screened against B. tabaci using a Y-tube olfactometer. Limonene, E-cinnamaldehyde, citral, cumin oil, and geraniol had a significant repellent effect on whiteflies, while the other oils did not. A dual-choice bioassay evaluated the significantly repellent oils, with and without kaolin clay, on whitefly-infested squash plants. Plants treated with E-cinnamaldehyde displayed phytotoxicity symptoms at the concentration tested. Among the remaining 4 compounds, citral applied alone repelled more whiteflies than limonene, geraniol, and an untreated control. Combining each oil with kaolin clay significantly improved their repellency compared to just the oil or kaolin alone. Combining limonene and kaolin was as effective as combining citral and kaolin despite citral being the most repellent compound on its own. This study demonstrates that kaolin clay has an additive effect for each oil tested, which may be used in an integrated pest management (IPM) program to extend the repellency duration against whiteflies in squash.