Repellent and Lethal Effects of Different Wavelengths of Light-Emitting Diodes (LEDs) Against Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae Koch, is a major agricultural pest that causes economic losses in the cultivation of most crops worldwide. Pesticide resistance and the phase-out of many active pesticidal substances have accelerated research into alternative methods for pest management. The effects of light-emitting diodes (LEDs) on plants, as well as their potential use in pest management, have attracted the attention of researchers for the last 25 years. In this study, the repellent effects of UV-A, blue, and red LEDs on T. urticae were investigated using choice tests in laboratory conditions. The lethal effect of red LED light on adult individuals was determined by a no-choice test. Importantly, red LED caused 67.0 ± 4.5% (mean ± SE) mortality in adults in the no-choice test. Second, the UV-A LED clearly had a strong repellent effect on T. urticae in the choice tests. In the “UV-A vs. white LED” and “UV-A vs. darkness” choice tests, the egg-laying percentage in the UV-A part remained below 0.55%. Furthermore, UV-A also had a significant repellent effect on T. urticae larvae. In the choice tests, the larval ratio in the UV-A part was less than 5%. The results of laboratory experiments indicated that red and UV-A LEDs have significant lethal and repellent effects on T. urticae. Comprehensive investigations should be performed in greenhouses using different strategies to optimize how these potential effects can be used in pest management.