Why does the effectiveness of light trapping for tea leafhoppers decline sharply in late autumn?

Light trapping is a common monitoring and control method for Empoasca onukii Matsuda (Hemiptera: Cicadellidae), a major pest in tea gardens. However, in late autumn (late October), despite large populations of leafhoppers in tea gardens around 30°N latitude, the effectiveness of light trapping declines sharply. The factors causing this decline are unclear. In this study, field experiments revealed significant differences in ambient temperature and photoperiod corresponding to variation in light trapping effectiveness across different leafhopper peaks. Through a series of bioassays, we found that leafhoppers on and off of the host plant showed opposite behavioral responses to light stimulation; leafhoppers on the host exhibited negative -phototaxis, while those off the host showed positive phototaxis. Both behaviors were influenced by the light wavelength and intensity, with response intensity increasing linearly with light intensity. The phototactic rate increased with temperature within 10°C to 30°C, reaching a maximum at 30°C before decreasing. For males, the phototactic rate increased with the photophase of the rearing photoperiod extended. These results provide the first evidence that changes in photoperiod affected the -phototactic behavior of E. onukii. Low temperatures and short photoperiods caused the sharp decline in light trapping effectiveness for tea leafhoppers in late autumn, providing crucial information for the application of light trapping in leafhopper control.