| Tea green leafhopper(Empoasca Cicadellidae) is one of the most harmful pests in tea plantations in China. The species has 9-11 generations per year and only feeds on tea plant whole year (without heteroecism). The nymphs and adults suck sap from young tea shoots and leaves causing damage called hopperburn. Until recently, most tea farmers used chemical pesticides as the main method for the leafhopper control, which results in serious pesticide residue on tea leaves. Alternative control methods such as yellow sticky traps and light traps are expanding and widely used in tea plantations in China, to replace pesticides in organic farms. In this thesis, the changes of three important behavioral activities and mating behavior of adult tea green leafhopper were examined when treated under varying photoperiods or light wavelengths indoor. The study also expressed the difference of phototaxis between females and males, both in daytime and at night, and the controlling effects of illumination without trap at night under varying wavelength treatments. Here are the main results:1. Identification of tea green leafhopper in Fujian, ChinaI sampled tea green leafhoppers from south, central and north regions of the Fujian province to determine which species were present and which one was dominant. The main taxonomic characteristics were the male adult genitals. Our results showed that all 514 male adult leafhoppers identified in this study belonged to Empoasca onukii Matsuda (1952). Hence, the dominant species of tea green leafhopper in the mentioned tea plantations have great potential to be E. onukii, instead of E. vitis, which was thought for a now time to be the main pest in the province.2. Behavioral responses of adult E. onukii under varying indoor light conditionsThe behavior of the tea green leafhopper, Empoasca onukii Matsuda, was examined when exposed to different light photoperiods or wavelengths. Observations included the frequency of locomotion and cleaning activities, and the duration of time spent searching. The results confirmed that the adults of E. onukii, both females and males, are more active in darkness (or at night when under normal photoperiod) than in light. In continuous darkness (DD), the locomotion and cleaning events in Period 1 (7:00-19:00) were significantly increased, when compared to the leafhoppers under normal photoperiod (LD). Leafhoppers, especially females, changed their behavioral patterns to a two day cycle under DD. While in continuous illumination (LL), yellow light at night (LY) and green light at night (LG), the activities of locomotion, cleaning and searching were significantly suppressed during the night (19:00-7:00) and, locomotion activities of both females and males were significantly increased during the day (7:00-19:00). Our study also demonstrated that the suppressing effects varied among LL, LY and LG. Under green light the suppression was higher than the other conditions. My work suggests that changing of light conditions, including photoperiod and wavelength, can influence the behavioral activities of leafhoppers, which probably influence their reproductive behavior.3. Mating responses of adult E. onukii under varying indoor light conditionsIn this work, mating behavior of one couple alone and ten couples together of E. onukii under normal photoperiod was observed and described. The mating responses by adding different wavelength illuminations (yellow light or green light,) during Period 2 were recorded and analyzed. When under standard photoperiod, no matter whether it was one or ten couples, after emergence, the mating started on day 5 and peaked on day 6 to 8. For the 10 couples, there was an average of 7.6 mating events, and 70.2 minutes for one mating event. Most,73.7%, of the copulation happened during Period 2 (19:00-7:00), and among them, more than 50% occurred between 19:00 and 21:00. Changes in light conditions significantly affected the mating activities, such as delayed the peak of mating events (1 day delay under yellow light at night and 5 days delay under green light at night), deceasing of mating events (6.8 for yellow light treatment and 5.6 for green light treatment), shortened the mating duration (63.4 minutes under yellow light treatment and 59.9 minutes under green light treatment), and increasing trend of more mating events in daytime (46.2% of mating happen at night with yellow light, only 16.3% happen at night with green light). My work suggests that light can affect the mating performance of E. onukii, therefore may influence the oviposition and the population size of the next generation.4. Responses of adult E. onukii under varying outdoor light conditionsIn this study, an open field experiment was designed to test the phototaxis of tea green leafhopper in day time (by yellow sticky card) and at night (by three different wavelength light traps). The effects of pest management using yellow sticky cards and three light traps in tea plantation were also examined. Weather conditions were taken into consideration in this experiment. In addition, the effects of population dynamics of E. onukii under different light conditions were tested with an exclosure experiment. The results proved that all the three LED light traps (white, green and yellow) and yellow sticky cards attracted much more E. onukii male adults than females during the course of open field experiment, with fewer than 30% of trapped adults being females. The weather conditions significantly influenced the number of tea green leafhopper trapped, but this variation was also influenced by the trapping methods. The daily number of leafhoppers trapped by green and yellow lights was positively related to the rainfall. There was no significant relationship between rainfall and yellow sticky card treatment, but there was a significant negative correlation with solar radiation. In the exclosure experiment, I went further to prove that the yellow sticky cards were not an effective control method. Compared to the control, the population of leafhoppers in the yellow sticky card treatment did not decline significantly. On the other hand, the green and white light treatments (without traps) showed significant control of E. onukii. These results suggest that yellow sticky traps and light traps have limited capacity to control adult tea green leafhoppers, especially for the females. On the other hand, they could be a promising population control system for leafhoppers in tea plantations or agricultural crops, not as death traps, but rather as a behavioral control system. |
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