| Myzus persicae (Sulzer), also known as green peach aphid, is the main pest for tobacco and widely distributed in each tobacco growing area in China. In this dissertation, we took M. persicae as the object of the research, and combined the push-pull principle with geo-statistical analysis to investigate the population dynamics and the field distribution pattern of M. persicae in Enshi tobacco growing area. Based on the influence of Aphidius gifuensis (Ashmead), Harmonia axyridis (Pallas), aromatic plants and tobacco varieties to M. persicae population, we formulated and evaluated the effect of ecological control measures to M. persicae in tobacco fields, all of which provided a scientific basis for integrated control of M. persicae. The results of the research were as follows:1The distribution patterns of M. persicae and its natural enemies A. gifuensis and H. axyridisThe density of M. persicae was minimum in tobacco seedling stage, and maximum at tobacco fast-growth stage in Enshi. The coefficients of variation were large in all developmental stages of tobacco, indicating the inhomogeneity in spatial distribution. Population density distribution curve was right skewed, proving the growing rate was faster than the extinction rate. The kurtosis of population distribution curve in tobacco seedling stage was significantly larger than those in other stages and showed a higher aggregation at that time.The population dynamics of alate M. persicae presented bimodal curve. It peaked at the third week after tobacco transplanting and the second week after tobacco decapitation. The population dynamics of apterous M. persicae, however, presented unimodal curve and peaked one week later than did the alate ones. In the vertical direction, there were two distribution peaks in the curve of population dynamics of alate M. persicae, while only one in that of apterous M. persicae in all tobacco stages.In different horizontal directions, the spherical model and the nested model of spherical+Exponential are the main spatial distribution models to fit the spatial distribution of M. persicae, of which both fall into the category of aggregated distribution. The nugget and sill increased with the field population density, and the range varied with time and place, indicating that the spatial correlation distance varied with conditions. A. gifuensis occurred three weeks later than did M. persicae in Enshi, and the lag time was longer than that in Yunnan (10days). H. axyridis naturally occurred2weeks later than did M. persicae. The time niche breadth values of apterous M. persicae and A. gifuensis were respectively0.2368and0.2527and the niche overlap index was0.9011, showing a high degree of niche overlap and an obvious interspecific interaction effect. The niche overlap index between apterous M.persicae and H.axyridis was0.9446, showing an obvious interspecific interaction as previously noted. However, the niche overlap index between A. gifuensis and H. axyridis was low, indicating an unobvious interspecific competition within the scope of the investigation.The population variation coefficients of M. persicae, A. gifuensis and H. axyridis were all large, indicating the inhomogeneity of population distribution. Skewness was skewed to the right, indicating the faster growing rate than the extinction rate. The population kurtosis of M. persicae was larger than that of A. gifuensis and H. axyridis. The occurrence of M. persicae peak was shorter and more gathered under the action of natural enemies. Throughout the tobacco growing stages, A. gifuensis and H. axyridis can be fitted with spherical model and nested model of spherical+exponential, both presenting aggregated distribution. A. gifuensis and H. axyridis had a following effect with M. persicae. At the occurring peak of H. axyridis, the number of M. persicae decilined more rapidly, and the effect was more obvious when compared with A. gifuensis.2Ecological control of M. persicae2.1Parasitic capacity of A. gifuensis to M. persicaeA. gifuensis is the dominant parasitoid of M. persicae in the tobacco growing area of Enshi. Experimental results showed that the parasitism rate of A. gifuensis to M. persicae was highest, up to63.2±15.8%, followed by that to turnip aphid Lipaphis erysimi (Kaltenbach) which was24.2±12.7%, but A. gifuensis was unable to effectively parasitize pea aphid and alfalfa aphid. The half-time of emergence of M. persicae mummies caused by A. gifuensis was15.6±1.5days, while that of L. erysimi was23.2±4.1days, and the difference reached a significant level. As the best host for A. gifuensis, M. persicae can be used as the main host for mass-rearing of A gifuensis.2.2Controlling effects of H. axyridis on M. persicae H. axyridis is the dominant predator of M. persicae. The developmental duration of the larval H. axyridis feeding on M. persicae and L. erysimi was significantly shorter than that on the Acyrthosiphon pisum (Harris) and Aphis medicaginis (Koch). H. axyridis preyed527M. persicae in total at the larval stage. One adult preyed135aphids every day and about10000aphids in total at the whole adult stage which last for80days or so. The adult did not lay eggs in the first7days, which was refered to as pre-oviposition stage; the oviposition peak was in day8to17, with a daily fecundity of32.5eggs in average. The18-57th days were the mid-oviposition stage, with a daily fecundity of11.64eggs on average, followed by post-oviposition stage after58days, with a daily fecundity of3.78eggs in average. A female laid1006eggs on average the whole life. Collectively, H. axyridis could effectively control the populations of M. persicae.Under the starvation condition, the hunger-enduring time for1st-4th instar larvae of H. axyridis were27.8h,46.5h,60.6h and144.1h on average, respectively; the crawl speeds of1st-4th instar larvae were respectively0.16cm/s,0.76cm/s,0.87cm/s and1.57cm/s; and the crawl distances were respectively143.48m,1207.36m,1787.91m and7631.43m. Except the adult H. axyridis, the4th instar larvae of H. axyridis crawled the most quickly, and had a strongest ability of foraging and preying in the field, so they could be used for field releasing.2.3The lure and expelling characteristics of aromatic plants to M. persicaeAmong all the aromatic plants, perilla had a relatively higher ability to expel M. persicae. Intercropped in the tobacco fields, perilla can expel M. Persicae from tobacco. Konghuang had the strongest ability to lure and trap the M. persicae, it would contribute to aphid management when intercropping around the tobacco fields. Kongcheng and marigold had no prominent ability to lure or expel M. persicae.2.4The effect of tobacco varieties on population density of M. persicaeAmong84varieties in five categories of tobaccos growed Enshi tobacco-growing areas, Oriental tobacco and Sun-cured yellow tobacco saw a higher population density of M. persicae, while Burley tobacco and Maryland tobacco had a higher resistence to M. persicae. Canik was the most susceptible among the three Oriental tobacco varieties. Hunan Ningxiang sun-cured tobacco, Baihuatiegan Mao Yan and Mazixi Mao Yan were more susceptible among13Sun-cured yellow tobacco varieties. ZhongYan103, guangdong smoke98, CB-1, HB074, HB023and Honghua Dajinyuan were more susceptible among20Flue-cured tobacco varieties. Tennessee90, Ebai21, Jianshi2, Kentucky16and YNBS1were more susceptible among40Burley tobacco varieties. Wufeng1was the most susceptible among five Maryland tobacco varieties. In addition, Hunan Ningxiang sun-cured tobacco, Baihuatiegan Mao Yan, Canik, Mazixi Mao Yan were the most susceptible among all tobacco varieties. Those should not be planted in areas the M. persicae frequently occurred.2.5The effect of ecological control of M. persicae in the fieldH. axyridis, A. gifuensis and aromatic plants were used and evaluated for the effect on ecological control of M. persicae in the field. The results showed that four days after A. gifuensis release at the parasitoid/host ratio of1:100, the population of M. persicae was still increasing, but declined to below0.5after14days, indicating an obvious hysteresis effect. The population of M. persicae, however, continuously declined and the population density index fell below0.5in8th days when H. axyridis was released at the predator/prey ratio of1:200. Although both A. gifuensis and H. Axyridis can effectively control M. persicae, it seemed that H.axyridis is the best ecological control agent due to its immediate effect and lasting role in controlling M. persicae.Intercropping with anthelmintic aromatic plants such as perilla in field could effectively expel and reduce the population size of alate M. persicae, but also expelled A.gifuensis and H.axyridis to an extent. While intercropping with insect-luring aromatic plants like Konghuang in the field, the population of M. persicae on the tobacco still growed. Therefore, insect-luring aromatic plants can not be used as ecological control agents.Based on the research mentioned above, we formulated an ecological control system for M. persicae suitable in Enshi tobacco-growing area.(1)According to the industrial demand and local characteristics, variety Segedinska Buca, Eyan1, and Yunyan85should be given priority in growing when it comes to Cigar, Burley, and Flue-cured tobacco, respectively. Meanwhile, intercropping with insect-resistant aromatic plants such as perilla in the tobacco fields can further reduce the population number of M. persicae.(2) Because of industrial demand and local characteristics, the susceptible varieties must be cultivated in some tobacco growing areas. In that case, the adult of H.axyridis can be released at the predator/prey ratio of1:200within one month after transplanting, when the M. persicae density is low (less than30aphids/plant), to control the population of M. persicae in the fields.(3) M. persicae often break out in local areas (The population reached100aphids/plant) due to special reasons. Then, the4th instar larvae of H.axyridis can be released in tobacco fields at the predator/prey ratio of1:200. In addition,100adult H.axyridis individuals per mu can be released as supplement to effectively control the M. persicae. |
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