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61.
Biological control is proposed as an ecological strategy to manage the threat of invasive plants, especially in natural areas. To pursue this strategy, we need to know that the host specificity criteria used to evaluate ecological risk with deliberate introduction of an exotic insect for biocontrol are sufficient to predict potential impact on native species. Host specificity is defined by adult feeding and oviposition preferences and larval development. One way to evaluate the criteria is to re-examine case histories where ecological effects are recorded, such as that of Rhinocyllus conicus Frölich. This flower head weevil, released in North America in 1968 to control exotic thistles like Musk thistle (Carduus nutans L), is now reducing seed production by multiple native North American thistle species (Cirsium spp.), and local population density of Platte thistle (Cirsium canescens Nutt.). We hypothesized that host specificity of R. conicus has changed since pre-release testing, providing an explanation for the unexpected magnitude of the documented ecological effects. Instead, when we re-tested host specificity of weevils naturalized over 28 generations, we found that host specificity has not changed. Naturalized adults of R. conicus showed strong feeding and oviposition preference for Musk thistle over Platte thistle. In addition, larval development by these weevils was faster and more successful (to larger size) on Musk thistle than on Platte thistle. Thus, our results indicate that a change in host specificity cannot explain the unexpectedly large build-up of R. conicus and significant ecological effect on Platte thistle. We conclude that accurate prediction of the potential level of impact on native host plants in the field requires further ecological information in addition to host specificity. 相似文献
62.
T. N. Ul'janova 《Genetic Resources and Crop Evolution》1997,44(1):5-8
The paper presents a survey of the situation existing now in nature with wild relatives of crop species from the group of segetal and ruderal plants, found within the territories of Russia and of other CIS countries. The majority of non-specialized annual and perennial weeds have been shown still to occur in the territory of the former USSR. For the past 50 years they have not seriously vanished from agriculture. Some of them even have a tendency to expand their areas and to become more abundant. Hence they need not be conserved in gene banks. It is only for a relatively small group of species of specialized contaminants that care should be taken to preserve them and to store their seeds in gene banks. 相似文献
63.
Exotic plant invasions threaten ecological communities world-wide. Some species are limited by a lack of suitable pollinators, but the introduction of exotic pollinators can facilitate rapid spread. In Tasmania, where many non-native plants are naturalised, exotic honeybees (Apis mellifera) and bumblebees (Bombus terrestris) have become established. We determined how these species affect the pollination of Lupinus arboreus, an invasive, nitrogen-fixing shrub, which is rarely visited by native pollinators. The proportion of flowers setting seed and the number of ovules fertilised per flower were positively related to the visitation rates of both exotic bee species. There was no effect of bee visitation rates on the proportion of seeds aborted prior to maturity, possibly due to post-fertilisation environmental constraints. We conclude that the spread of B. terrestris may not alter the fecundity of L. arboreus because of the pollination service provided by A. mellifera, and discuss potential interactions between these two bee species. 相似文献
64.
北方地区的旱直播稻田杂草群落属于水旱共生型复合群落,具有2个杂草发生高峰期,第1次高峰期为旱生型杂草,第2次高峰期以水生及湿生型杂草为主导群落.用百草枯除苗前大草,秧苗3叶期用“快杀稗+苯达松”茎叶处理,杂草综合防效可达95%以上. 相似文献
65.
采用农民乐防除休闲地杂草,结果表明,74.7%农民乐对苣荬菜的防除适宜剂量为1 500g.hm-2;对野胡萝卜为750—1 050g.hm-2;赖草、硬枝早熟禾为2 250g.hm-2;对西伯利亚蓼、三脉紫菀、茵陈蒿为3 000g.hm-2。 相似文献
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沿江圩区主要农作物病虫草害演替呈现以下特点 :种类增加 ,不断出现新的病虫为害 ;危害期拉长 ,发生程度加重 ;突发性病虫暴发成灾 ;螟虫危害趋于复杂化等。为此制定了近期与长远期综合治理措施 ,及时有效地控制其危害 相似文献
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