Effects of white LED light on reproduction of Conopomorpha sinensis (Lepidoptera: Gracillariidae) and its field application

Abstract: 【Objective】In this study, we explored the effects of white LED light on the reproductive bio- loge of Conopomorpha sinensis adults, and comprehensively evaluated the field trial efficiency by uti- lizing white LEDs to control C. sinensis, so as to provide a theoretical basis for the large-scale promo- tion and utilization of white LED light to control litchi fruit borer in the future【. Methods】The effects on five behaviors were observed, including moving, nutrition supplement, resting, mating and oviposition of adults at different light intensities (0, 5, 10, 50, 100 and 500 lx) at night, and the difference in adults fecundity and longevity were rocorded. The observation was executed under weak red light every 60 minutes for 6 consecutive days. The light period was set from 06:00 to 19:00, and the dark period was set from 19:00 to 06:00 of the next day. To comprehensively evaluate the field trial efficiency by utiliz- ing white LEDs to control C. sinensis, the adult populations, fresh eggs number on the fruit and pedicle borer rate of fruits were continuously investigated. The experiment began in the evening of March 16, 2020. Initial population number of the adults in the treatment and control areas were investigated during  the first daytime. Thereafter, the investigation was conducted every 7 days until the litchi fruit harvest. With both the treatment and the control, 7 and 5 trees were randomly selected, respectively.【Results】Behaviors of adults were affected to different degrees under the various light conditions at night. In the absence of light interference (light intensity=0 lx), 2-3 day-old adults were extremely active at night, mainly crawling or flying, mating and feeding, which was approximately dominated 80% of the time. The resting frequency increased gradually from 4 day-old adults, and nearly 70% of the time were rest- ing at 6-day-old at night. The mating behavior mainly occurred in 2-3 day-old adults, and the peak of mating was 3 day-old adults. Oviposition behavior of 2-4 day-old adults was rarely observed, and the proportion of oviposition behavior began to significantly increase with 5 day-old adults. Comparing with the dark treatment, 5-10 lx light intensity significantly inhabited the activity of adult moving, mat- ing and oviposition behaviors; 50-100 lx light intensity inhabited not only the activity of moving, mat- ing and oviposition, but the time for the first mating, and oviposition was also delayed by 3-4 days; when the light intensity increased to 500 lx, the adults were basically in the resting state, occasionally moving or feeding, and no mating and oviposition occurred. After the white LED light was utilized to control litchi fruit borer, adult populations, fresh eggs number on the fruit and pedicle and borer rate with treatments were significantly lower than those with the control. The results indicated that the initial population number of the treatment and control was 0.86 and 1.50 per tree, respectively. Subsequently, the adult population number of the treatment was rarely fluctuant in the various investigation periods, only 1.57 per tree at a maximum. However, the adult population number in the control rapidly in- creased, significantly higher than the treatment in the same period. At peak period, 18.75 per tree were recorded, 10 times more than the treatment. Fresh eggs number on the fruit (FENF) of the treatment and the control were 0.11 and 0.15 per fruit, respectively. Subsequently, the FENF of the treatment began to decrease dramatically, which was significantly lower than that of the control during the same period. The FENF with the control rapidly increased after the experiment began. At peak period, 0.81 per fruit was recorded, 50 times more than FENF of the treatment. Pedicle borer rate of dropped fruits (PBRDF) of the treatment and control was very low, only 5.71% and 6.25% , respectively. After 7 days, the PBRDF of the treatment and the control dramatically increased, with average of 57.86% and 70.25%, re- spectively. Subsequently, the PBRDF with the treatment rapidly decreased in the last three investiga- tions, while the control still remained at 50%-80%, significantly higher than the PBRDF of the control during the same period.The initial pedicle borer rates of fruits (PBRFT) of the treatment and control were 1.43% and 2.5%, respectively. The low PBRFT with the treatment maintained before harvest, not exceeding 5%. On the contrary, subsequent PBRFT with the control gradually increased in the subse- quent six-time investigations, floating between 9%-20%.【Conclusion】The LED white light at night can inhibit the behaviors of C. sinensis, and the inhibitory effect increased along with crescent light in- tensity. However, there was no significant effect on biological characteristics such as fecundity, egg hatchability and longevity. Utilization of LED white light in the litchi orchard can significantly reduce the adult populations and oviposition on the fruit, thereby protecting the fruit from this pest damage.