首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   8篇
  免费   1篇
  2022年   1篇
  2021年   1篇
  2018年   1篇
  2006年   1篇
  2005年   1篇
  2000年   1篇
  1996年   1篇
  1995年   1篇
  1982年   1篇
排序方式: 共有9条查询结果,搜索用时 15 毫秒
1
1.
The distribution of Rastrococcus invadens among different host plants and the impact of the mealybug on mango growth were investigated on 2067 trees in three surveys across all the ecological zones of Benin. The first survey started in 1989, less than 1 year after the first release of the exotic parasitoid Gyranusoidea tebygi. Within 3 years, G. tebygi had colonized the entire area of infestation, and was found on practically all infested mango trees as well as other infested host plants. By 1991, the incidence of R. invadens on the secondary host plants had declined significantly. The percentage of infested mango trees declined from 31.0% in 1989 to 17.5% in 1991, highest populations being found in the coastal savanna. During the same period, the mean percentage of infested mango trees having indigenous predators declined from 42.3 to 20.9%. Average mealybug densities declined steadily from 9.7 females/48 leaves in 1989, with 3.2% of all mango trees having densities above 100 mealybugs, to 6.4 females/48 leaves in 1991, with 1.3% of all trees having densities above 100 mealybugs. In multiple regression analyses, based on 23 meteorological, agronomic and plant variables, the duration of the parasitoid's presence proved to be a major factor. It influenced mealybug population densities and sooty mould incidence, which, in turn, affected the production of new leaves. In all analyses, the impact of rainfall, for example, on the sooty mould or the mealybug was less important than the effect of G. tebygi. The present study demonstrates for the first time on a large scale the impact of G. tebygi on R. invadens and, indirectly, on its main host plant, mango.  相似文献   
2.
Many ant species are highly invasive and are a significant component of disturbed ecosystems. They can have a major suppressive effect upon indigenous invertebrates, including other ants. Despite overwhelming circumstantial evidence for the ecological resourcefulness of many ants, there appears to be no experimental evidence illustrating the habitat breadth of a potentially invasive ant species. We demonstrate here that a particularly opportunistic and locally dominant ant Anoplolepis custodiens, which is a major indigenous African pest, overrides habitat structure to maintain its population level. We compared A. custodiens activity, morphology, foraging behaviour and ant species diversity in artificially established surrogate habitats (cover crops) in a vineyard containing an ample food resource in the form of the honeydew-producing mealybug Planococcus ficus. These cover crops were chosen so as to create highly altered habitats. The ant's ability to overcome these potentially suppressive habitat conditions hinged on its tight mutualism with the mealybug, and on its chasing away mealybug parasitoids. This ant species is predicted to be a latent invasive beyond Africa. It is unlikely to be impeded once it has established a foothold in a variety of novel habitats. It could locally invade to obtain food resources in a wide range of habitat types. Furthermore, in agricultural systems, cover crops are unlikely to control such an ant. Potential invasives such as this ant should be flagged as important quarantine suspects.  相似文献   
3.
4.
This study investigated the impact of released exotic mango mealybug parasitoid Gyranusoidea tebygi on mango mealybug Rastrococcus invadens in Nigeria. Observations were also made on the occurrence of the mealybug on other host plants in the surveyed areas. The monitoring exercise started in 1991 about 2 years after the first release in Ibadan. By 1997 and 1998, G. tebygi was found to have crossed all agro-ecological barriers to colonize the entire area of infestation nationwide on mango as well as other host plants. During this period, the populations of R. invadens had greatly decreased from between 11.0 and 98.0 mealybugs per leaf in 1991 to between 0.0 and 18.2 mealybugs per leaf in 1998. This fall was attributed to the activities of the released parasitoid. At many sampling sites in 1998, mealybugs were virtually absent on both mango and other host plants. Predators that were observed during the survey, were the coccinellids: Exochomus promptus Weise, Chilocorus nigritus (F) and Nephus spp. Larvae of chrysopid species, Ceratochrysa autica (Walker) and Plesiochrysa sp. The hyperparasitoids reared from mummies were Marietta leopardina Motsch (Aphelinidae), Chartocerus hyalipennis Hayat and Chartocerus subaeneus (Forster) (Signiphoridea).  相似文献   
5.
The methylation status of the nuclear DNA from a mealybug, aPlanococcus species, has been studied. Analysis of this DNA by High Performance Liquid Chromatography and Thin Layer Chromatography revealed the presence of significant amounts of 5-—methylcytosine. Since analysis of DNA methylation using the Msp I/Hpa II system showed only minor differences in susceptibility of the DNA to the two enzymes, it seemed possible that 5-methylcytosine (5mC) occurred adjacent to other nucleotides in addition to its usual position, next to guanosine. This was verified by dinucleotide analysis of DNA labelledin vitro by nick translation. These data show that the total amount of 5-methylcytosine in this DNA is slightly over 2.3 mol %, of which 0.61% occurs as the dinucleotide 5mCpG, 0.68% as 5mCpA, 0.59% as 5mCpT and 0.45% as 5mCpC. 5mCpG represents approximately 3.3% of all CpG dinucleotides. The experimental procedure would not have permitted the detection of 5mCp5mC, if it occurs in this system. Unusually high amounts of 6-methyladenine (approximately 4 mol %) and 7-methylguanine (approximately 2 mol %) were also detected, 6-methyladenine and 7-methylguanine occurred adjacent to all four nucleotides. The total G+C content was 33.7% as calculated from dinucleotide data and 32.9% as determined from melting profiles.  相似文献   
6.
The study of thermal tolerance and acclimation capacity in Jack Beardsley mealybug, Pseudococcus jackbeardsleyi Gimpel and Miller is the crucial step in determining their abilities to cope with climate change. Thus, the aim of this research was to determine the effects of acclimation temperatures on the changes in thermal tolerance of P. jackbeardsleyi. The influences of acclimation temperature at moderate (25?°C) and high (35?°C) temperatures on their lower and upper thermal limits were measured composed of critical thermal minimum (CTmin), maximum (CTmax), chill coma temperature (CCT) and heat coma temperature (HCT) for first instar nymphs and adults. The important information derived from this study revealed that the upper thermal limits of adults are constrained to a relative narrow range that will make them sensitive to relative small changes in temperatures, whilst all mean upper thermal indices at 35?°C were significantly higher than at 25?°C for nymphs. For this highlight notice, nymphs have more potential to change their upper thermal limits which will allow them to withstand high temperatures in the field. These results are a sign to warn us that P. jackbeardsleyi could become highly noxious which cause severe outbreaks damage to the crops in the tropics under global warming.  相似文献   
7.
Chlorpyriphos is one of the major organophosphorus pesticides used widely to control a range of insect pests across several crops. This insecticide is hazardous to the environment and toxic to mammals, thus, it is essential to remove the same from the environment. Similarly, use of polythene is also increasing day by day. Therefore, it is highly important to identify ways to degrade chlorpyriphos and other pesticides from the environment. We studied the degradation of chlorpyriphos and polyethylene by Citrus mealybug (Planococcus citri) bacterial endosymbionts such as Bacillus licheniformis, Pseudomonas cereus, Pseudomonas putida and Bacillus subtilis. This investigation revealed that bacterial endosymbionts use the polythene as a source of carbon and solubilize them by their enzymatic machinery. The degradation of polyethylene by endosymbionts showed a significant reduction in weight of polyethylene sheet after 15, 30 and 45 days of treatment. The SEM images showed localized degradation of the polyethylene around the bacterial cells in the biofilm. Further, the tensile strength (percentage elongation) was significantly reduced after 45 days of incubation. The weight of paraffin wax showed significant reduction in B. cereus. A significant reduction in total amount of chlorpyriphos in soil was observed at an interval of 7, 14 and 21 days after treatment by the bacterial isolates. Among the bacteria, B. cereus and P. putida were found to be most effective. The results from this study show that endosymbionts can be significantly implicated in degrading chlorpyriphos and polyethylene from the environment.  相似文献   
8.
粉蚧是农林经济作物的一类重要害虫,由于体表覆盖一层蜡粉,化学防治常需要大剂量反复用药该虫才能得以控制,易造成环境污染及害虫再猖獗。本文从昆虫化学生态学的角度综述了粉蚧类害虫的寄主植物范围、天敌应用以及三重营养关系研究进展,归纳已鉴定粉蚧性信息素化学结构特点及其在综合防治中应用概况,探讨粉蚧类害虫化学生态学未来研究方向,为其绿色防控提供理论基础。  相似文献   
9.
Coccidoxenoides perminutus achieves only low levels of parasitism of its host Planococcus citri in southeast Queensland citrus. Two possible causes were investigated. Adult survival under natural conditions was assessed to determine whether providing adult food sources could enhance survival. Behavioural changes of hosts, induced by C. perminutus parasitism, was also investigated to establish if parasitised P. citri move from their feeding site to seek protected shelters some distance away and are thus not accounted for in field assessments of parasitism rates. Unparasitised mealybugs placed in the field for two periods were retrieved before the effects of parasitism were manifested and parasitism rates were still low (0.3% at 5 days and 1.2% at 10 days). Levels of locomotion of P. citri exposed to C. perminutus were compared with those of “unexposed” ones. Parasitised mealybugs, regardless of instar, undergo behavioural changes. In comparison to unparasitised controls, the mealybugs become highly active 7–14 days after exposure to wasps. All parasitised mealybugs undergo physical changes, their body becomes cylindrical, their legs go so rigid that the mealybugs become immobile, and this signifies the typical mummy appearance. All mealybugs that became mummies eventually fell from the host lemon fruit because of impaired locomotion and were caught on sticky traps that had been placed beneath the lemons. Consequently, their final site of mummification was not established. C. perminutus adults provided with nectar or honey survived longer (about 5 days) in the field than those without food (about a day). Nectar from two plant species, Alpinia zerumbet and Datura candida, proved to be good sources of food for the adult wasps, and were comparable in quality to honey. The low level of parasitism achieved by C. perminutus in southeast Queensland citrus thus appears to be a consequence of the short adult life and the negative effects of a harsh environment. Provision of a suitable food source (e.g., nectar) may well enhance levels of parasitism in the field.  相似文献   
1
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号