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Study on Bioligical Characteristics and Control Techniques of Dendrolimus Superans in Aershan

Author: WangJiaFu
Tutor: LuoLiZhi
School: Chinese Academy of Agricultural Sciences
Course: Rural and Regional Development
Keywords: Dendrolimus superans Biology Ecology Cold hardiness Control
CLC: S763.421
Type: Master's thesis
Year: 2009
Downloads: 17
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Abstract


The larch caterpillar moth Dendrolimus superans Butler (Lepidoptera:Lasiocampidae) is an serious insect pest of the pine forest in the northeastern China and great yield has been loosed due to the serious damage of this pest. Focusing on the problems presented in the management and monitoring of D. sperans in Aeshan region, the biological and ecological characteristics and various management means for the D. superans in Aershan region were investigated to develop a better control strategy and techniques and reduce the economical loss caused by this pest and maintain the sustainable development of the forest industry in this region. The followings are the major significant results obtained in this study.The bionomics of adults, eggs, larvae and pupae of D. superants were studied by combined the analysis of the field and laboratory data. After the characteristics of emergency and mating, average fecundity and lifespan of the adult were confirmed, the fecundity of female adults were found to correlate to her pupal weight positively (y=-136+118.73x, R= 0.869, P< 0.05). which indicates the heavier the female pupae are the larger the fecundity of their adults have. The eggs are mainly located on the leaves, branches gaps of the bark of the pine trees which was determined by the investigations of all possible ovipositiong sites selected by the adults. The eggs experienced four different colors changed during their developments, and hutching of the eggs peaked in the first and second 10 days of August in the fields. The variations in the instars and developmental durations of the larvae were confirmed by comparison of the ontogeny of larvae from 1 generation per year (GPY) and 1 generation bi-year (GBY). There are 9 instars for larvae in GBY but only 7 instars for those in GPY. Larvae from GBY need around 660 days distributed in 3 years to complete their development while those from GPY need 290 days in two years to do it. The feeding periods for larvae in GPY and GBY are 155 and 290 days, respectively. The pupation began after the larvae stopped feeding and completed cocooning. The pupae could be found in the field from the last 10 days of May to the first 10 days of July, with a peak occurred in the middle 10 days of June. The characteristic of life history in D. superans in Aershan region is demonstrated and summarized as a life history graphic based on the above data.Damage and population density of D. superans in relation to the landscape ecology were further investigated after its life history characteristics in Aershan region was determined. Results obtained showed that the damage of the trees by D. superans in the sunny slope and at elevation 800-950m were more serious than other comparable locations. In addition, trees grown in the thin layer of soil subjected more serious damage than those grown in the thick soil profile.15 to 30a Health Larix forest seriously injured. D. superans occurred in a big cycle by10 years in Aershan region. However, mechanisms for the presence of these phenominan are not underestund at the present. There are 30 species of natural enemies attacked D. superans in Aershan region, including 19 species of parasitoids and 11 species of predators. The mortality rate caused by natural enemies could reach as high as 80% and they therefore play an important role in regulating the population dynamics of D. superans. D. superans populations behaved a cyclic outbreak based on analysis of the outbreak area in this region from 1979 to 2008. There is an outbreak in 10-years period each consisted of 3 to 7 years. And the later outbreak looks more serious than the previous ones indicating the damage of D. superans in Aershan region will be heavier and heavier. The cold hardiness of hibernating larvae was firstly investigated in Aershan region after the hibernating stages of D. superans were determined for the GPY and GBY. The supercooling point for the diapause and non-diapause larvae is-18.7℃and-5.7℃, respectively while the freezing points for them is-11.0℃and-2.4℃, respectively. The diapause larvae had a greater cold hardiness than the non-diapause ones for they had greater fat and free fatty acid but less water content. These results suggest that only the diapaused larvae could surpass the winter in Aershan region.The spatial distribution pattern of larvae distributes aggregately after their respective location on the trees were systematically sampled and analyzed. And a formula for calculating the optimum sample sizes was synthesized based on these data.Where x means the population density, and n means number of samples. This formula provides not only the referees for determining the sample sizes, but play a great role in reduction of the sampling labors.In order to develop effective control means of the D. superans population, several management means to control its damage have been tested and evaluated, which included artificial removing cocoon and egg masses, application of light traps, nest-trapping birds and bio-pesticides. All these skills are effectively reduced the damage of the pest population and can be used as a means in the integrated control program. In turn of the application of insecticides, several bio-pesticides with more than 85% of control efficacy were screened out, which included the 1.8% of avermectine,25% of diflubenzuron, and 20% of trifluralin and a couple of microcapsules. At the same time, the control efficacies of insecticide application methods including smoking, spraying, and ultra-low concentration spraying by aircraft were individually evaluated. All these insecticides and application means provided an effective means for suppressing the outbreak populations of D superans. Finally, reforming the manmade forest was also an effective manage means to suppress the population of D. superans. This is exemplified by the facts that 7.4 and 15.2 individuals of D. superans/tree are found in the reforming and the pure forest stands, respectively.All these results offer a firm basis for further demonstrating the bionomics and population dynamics, improving monitoring and management skills and reducing economical loss of D. superans in the given area.

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CLC: > Agricultural Sciences > Forestry > Forest Protection > Forest Pest and Disease Control > Pest and its control > Lepidoptera pests > Dendrolimi
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