| Rubber tree is a perennial rainforest deciduous tree, which is native to South America. Natural rubber is a kind of latex obtained by collecting from rubber tree, solidification and processing. It is different from genera industrial stuff and a kind of crucial strategic material. Natural rubber, coal, oil and steel are known as the four industrial raw materials, among which natural rubber is the only renewable raw material. China is the biggest country consuming natural rubber and the largest import nation in the world, but80%of the rubber depends on import.In recent years, the natural rubber industry has developed rapidly meanwhile the occurrence and harm of rubber plant diseases and pests become more and more serious, which restricts the stablility and yield of the natural rubber production. Parasaissetia nigra Nietner is a serious harmful, large in number and wide-spread pest in all rubber tree insects, it can do harm to the rubber seedlings and mature trees seriously, resulting in leaves becoming yellow, falling off and even the death of the whole tree. It has strong reproductive capacity, each female adult can lay1345eggs. The adults and nymphs feed on the tender branches and buds or leaves, the honey dew rich in sugars and amino-acids secreted by P. nigra Nietner can cause sooty mold and affect the photosynthesis. For a long time, the prevention and control of P. nigra Nietner mainly depended on chemical pesticides because the body wall of the pest is covered with hard shell and the rubber tree is too tall. It’s very difficult to prevent and control P. nigra Nietner. Recently, the concentration and frequency of chemical pesticide has been increasing, so the environment is polluted and insects get drug-resistant. At the same time the pesticides also cause damage to their natural enemies. Therefore, making full use of natural enemies to control and prevent P. nigra Nietner, the Ecological pest management(EPM) which pay more attention to ecological balance, will become the developmental trend of controlling pests.There are many natural enemies against P. nigra in nature. Metaphycus parasaissetiae Zhang and Huang is a kind of parasitoid and large in populations, which is an endoparasite living in P. nigra Nietner. This article investigated P. nigra Nietner in Rubber forest of Shatian team in the Baodao new village in Danzhou city, Heqing farm in Heqing town and Huaqiao farm in Dafeng town in Chengmai city in Hainan province. And the effect of different densities of M. parasaissetiae on the parasitic rate and the control efficiency is studied. The results are as follows:1.The spatial distribution pattern of P.nigra adults, nymphs and P.nigra adults parasitized by M.Parasaissetiae were studied by the methods of aggregation index and 2.Taylor’s law. The results of two methods showed that the spatial distribution pattern of the three insects talked above were aggregated distribution.3.1n tapped rubber plantation, when the density of M.Parasaisseliae released was1releasing implement per666.7m2(Ⅰ,about1724),2releasing implements per666.7m2(Ⅱ,about3448),4releasing implements per666.7m2(Ⅲ, about6894), the parasitic rate of M. Parasaissetiae was more than30percentage, and its control efficiency was more than39percentage; when the density of M. Parasaissetiae was Ⅲ and the tests lasted for90days, both the parasitic rate and the control efficiency reached the highest, its parasitic rate has reached47.96percentage, increasing3.22times compared with non-released, and the control efficiency was as high as64.21percentage.4.1n mid-age rubber plantation, when the density of M.Parasaissetiae released was1releasing implement per666.7m2(Ⅰ, about1936),2releasing implements per666.7m2(Ⅱ, about3872),4releasing implements per666.7m2(Ⅲ, about7744), the parasitic rate of M.Parasaissetiae was more than27percentage, and the control efficiency was more than30percentage; when the density of M.Parasaissetiae was Ⅲ (4releasing implement per area) and the tests lasted for90days, both the parasitic rate and control efficiency reached the highest, the parasitic rate was close to40percentage, increasing2.69times compared with non-released, and the control efficiency was nearly43percentage.5.1n young seedlings rubber plantation, when the density of M.Parasaissetiae released was1releasing implement per666.7m2(Ⅰ, about1856),2releasing implements per666.7m2(Ⅱ, about3712),4releasing implements per666.7m2(Ⅲ, about7424),the parasitic rate of M. Parasaissetiae was more than24percentage, and its control efficiency was more than27percentage; when the density of M.Parasaissetiae was Ⅲ (4releasing implement per area) and the tests lasted for90days, both the parasitic rate and control efficiency reached the highest, the parasitic rate reached32.79percentage, increasing2.25times compared with non-released, and its control efficiency was up to36.72percentage.6.1n three experimental locations where have different phenological phases of rubber trees, the parasitic rate of M.Parasaisseliae and the control efficiency were significantly different:tapped rubber plantation> mid-age rubber plantation> rubber young seedings; under the same density of M. Parasaissetiae released, with time of releasing lasted there was significant difference in the parasitic rate and the control efficiency:90d>60d>30d; At the same releasing time after M.Parasaissetiae released, with the increasing of its density there were significant differences in the parasitic rate and the control efficiency:Ⅲ>Ⅱ>Ⅰ.7.1n three study plots under three densities, the populations of P. nigra in the plantation released M.Parasaissetiae were all significantly lower than CK. Among the 8.densities, when the density is III, the reduction rate of P. nigra number was the fastest. In tapped plantation, mid-age plantation and rubber seedings plantation, the population of P. nigra has reducted65%,44%,42%after90days, respectively.This experiment studied the parasitic rate of encyrtids living in P. nigra Nietner and its control efficiency to P. nigra Nietner, providing a theory evidence to control and prevent P. nigra. |
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