Behavioural Responses of Spodoptera frugiperda (Lepidoptera: Noctuidae) to Powders of Three Invasive Alien Plants, Gleditsia triacanthos, Chromolaena odorata, and Schinus terebinthifolia: Repellence and Locomotion Patterns

Although the sublethal effects of botanical pesticides are critical for pest management, their role in modifying insect behaviour is frequently overlooked. In a laboratory bioassay utilising powder prepared from the leaf, stem, and root of the invasive alien plants (IAPs) Gleditsia triacanthos, Chromolaena odorata, and Schinus terebinthifolia, this study evaluated the behavioural reactions, notably repellence and locomotion, of Spodoptera frugiperda larvae. For repellence, six second instar larvae of S. frugiperda were individually placed in 30 mL vial that remained unsealed to allow larvae to exit freely if repelled and were exposed to 22% of leaf, stem and root powders of all three plant species over a 12 h period before recording the number of repelled insects. For locomotion, ten-second instar larvae were directly coated with different powder quantity 1.5 g and 2.5 g of leaf, stem, and root of all three IAPs, then released and allowed to move for 60 s on a 90 × 60 cm whiteboard. The running speed was calculated as the distance travelled per unit time. All plant-part powder exhibited significantly higher repellence than the control (0%). Gleditsia triacanthos leaf, root and stem powders showed minimal repellence, with values of 16%, 29% and 21%, respectively. However, higher rates were observed for C. odorata and S. terebinthifolia. Specifically, C. odorata stem powder achieved the highest overall repellence at 54%, whereas S. terebinthifolia performed best with its root powder at 45%. Compared to the control group, the running speed of the insects experienced a substantial reduction, decreasing by 60 to 80% when exposed to powders derived from all parts of the three IAPs. Our results suggest that the IAP powders used in this study both repel S. frugiperda and strongly limit their ability to move, highlighting their potential for behaviour-based pest control strategies.