Evaluation of repellent effects of plant-based essential oils, red dye, and kaolin on Asian citrus psyllid

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera: Psyllidae), vector of the pathogen causing Huanglongbing disease, is currently the most devastating pest of citrus. Despite intensive control efforts, the disease continues to spread. Diaphorina citri typically relies on tactile, visual, and odor cues for host selection. By combining an irritant (kaolin clay), a visual masking (red or blue dye), and true odor repellents, we aim to repel D. citri from citrus trees. In laboratory conditions, we conducted closed-cage bioassays to compare D. citri response to the following treatment combinations: (1) kaolin + food colorants (blue or red); (2) kaolin + odor repellents (thyme, lavender, fir, and coriander oil), and (3) kaolin + red food colorant + thyme oil. The red kaolin treatment exerted a greater deterrent effect on D. citri adults than the blue and uncolored kaolin treatments. We also observed an additive effect in terms of D. citri repellency with the combination of thyme-oil and kaolin and, to a lesser extent, coriander-oil and kaolin. However, the combination of lavender or fir oils and kaolin did not increase repellency against ACP as compared with kaolin alone. Thyme-oil + red kaolin oil combinations induced similar ACP repellency to that of thyme-oil + uncolored kaolin. Finally, fecundity was significantly reduced by the kaolin-based treatments compared to the thyme oil treatment and control plants. Our findings suggested the possible use of red kaolin or the combination of thyme and kaolin as a means of reducing D. citri infestation in citrus.