首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到10条相似文献,搜索用时 125 毫秒
1.
Altitudinal patterns in host suitability for forest insects   总被引:4,自引:0,他引:4  
Conspecific trees growing at high and low-elevations encounter different growing conditions and may vary in their suitability as hosts for herbivorous insects. Mountain tree populations may be more resistant to herbivory if low temperatures constrain growth more than they constrain photosynthesis, resulting in increased secondary metabolism (temperature hypothesis). Alternatively, mountain trees may be fertilized by atmospheric nitrogen deposition and become more palatable to insects (atmospheric deposition hypothesis). We evaluated these two hypotheses by comparing high- and low-elevation trees with insect bioassays and analyses of foliar nitrogen and condensed tannin. Contrary to the temperature hypothesis, high-elevation foliage had higher leaf nitrogen (six of six tree species) and allowed higher growth rates of Lymantria dispar larvae (five of six tree species). The nitrogen deposition hypothesis was broadly supported by measurements from two mountains showing that high-elevation trees tended to have higher leaf nitrogen, lower leaf tannins, and support higher insect growth performance than conspecific trees from lower elevations. The deposition hypothesis was further supported by fertilization studies showing that simulated atmospheric nitrogen deposition changed the foliar chemistry of valley trees to resemble that of high-elevation trees. Predictions that the altitudinal gradient in foliar chemistry and host suitability should be steepest on mountains receiving more deposition were largely not supported, but interpretations are complicated by lack of replication among mountains. In the northeastern United States, increased host suitability of high-elevation trees seems sufficient to influence the population dynamics and community composition of herbivores. Atmospheric nitrogen deposition offers a promising hypothesis to explain and predict some important spatial patterns in herbivory. Received: 21 September 1997 / Accepted: 12 June 1998  相似文献   

2.
Host specificity tests carried out in the laboratory in Australia during 1977, showed thatMicrothrix inconspicuella Ragonot could develop on young apple leaves (Harley et al., 1979). Field studies in unsprayed apple orchards in South Africa showed that some feeding occurred, but fewer than 40% of late instar larvae developed to adults when confined in sleeves on apple tree branches. No feeding or survival occurred in large field cages or in the open. Adults which developed from apple fed larvae were smaller, deformed, occasionally mated and laid fertile eggs but their progeny did not feed or develop on apple fruit or leaves. In conclusion,M. inconspicuella larvae did not develop on apple fruit or leaves in the field, damage was mainly limited to apples already injured and feeding on leaves was minimal. Under normal pest control practicesM. inconspicuella populations did not survive on any part of the apple tree or onE. australis growing under the trees.   相似文献   

3.
A population of the butterfly Luehdorfia japonica dependent on a small stand of an unusual host plant, Asarum caulescens, was found and observed for 5 years. The plant was growing in patchy clumps in a forest and in an adjoining clearing, but the number of leaves in the clearing decreased during the 5 year study period. Butterflies laid eggs mostly in or near the clearing, and the number of eggs steadily decreased year by year, along with the decrease in the number of leaves. The survival rate of the larvae was similar to that of the same species feeding on the usual host plant, Asarum takaoi, in an adjacent habitat. It is considered that A. caulescens is rarely a host of L. japonica because the plant grows in shady conditions and the butterfly prefers a host plant growing in a sunny locations for oviposition.  相似文献   

4.
The long-term population dynamics of the swallowtail butterfly, Papilio xuthus, were studied by means of life table analysis in a deforested area, where the host tree, Zanthoxylum ailanthoides, was growing. The number of eggs laid on host trees in the deforested area decreases as secondary succession progresses. When the trees were classified into three groups, i. e. tall, medium and short, according to their height relative to the surrounding vegetation, less eggs were laid on tall than on short host trees. Life tables for the natural populations in each generation were developed on the basis of mean values for 6 years. Eggs and larvae in early stages were attacked chiefly by small- and middle-sized predators, such as ants, spiders, bugs and orthopterids, while later stage larvae were attacked chiefly by birds or Polistes wasps. An inchneumonid wasp was the most important mortality factor in the pupal stage. Key-factor analysis was tested on the life table data of each immature stage. The late larval stage was a key stage, and most mortality factors were considered to operate independently. The test for density dependency did not show any tendencies. The analysis of variance in two-way classifications was carried out for the difference of survival rate among the tree groups. It was suggested that tall host trees were unsuitable for P. xuthus. The construction of life tables for artificially inoculated populations on large host trees showed that high physiological death rate were characteristic of such trees in comparison with natural populations on smaller trees. The characteristics of the population dynamics of P. xuthus in the deforested area are compared among some kinds of the habitat, and the interrelationship between P. xuthus and its host plant are discussed.  相似文献   

5.
Globally, Euphydryas maturna is a polyphagous butterfly species. At our study sites in Italy and Germany however, the plant used for egg-laying was almost exclusively Fraxinus excelsior. Nevertheless, in Germany, two egg-batches were found on Ligustrum vulgare and one on Viburnum opulus. Females lay their egg-batches at low heights and mostly on small trees (but not <1 m). At the end of the flight season, small egg-batches are laid and we conclude that these are late batches laid by “old females”. Egg-batches and pre-diapause larval webs are often clustered on certain trees and even leaves. This was shown to be a result of female behaviour and not of habitat quality, since the trees chosen were different in subsequent years. Individual females may return for laying further egg-batches to the place of the first egg-deposition and other females follow, since the survival of pre-diapause larvae is higher when more larval webs are on one tree. A further possible advantage during hibernation is discussed. In Italy, post-hibernation larvae form two distinct cohorts: larvae feeding on herbaceous plants (Plantago major, P. minor, Veronica hederifolia), and larvae feeding on Fraxinus excelsior. Although the latter group starts feeding later and pupates later, it reaches the same pupation weight. At our German site, post-hibernation larvae were found almost exclusively on F. excelsior. In fact, we observed larvae searching for food on F. excelsior while the buds of this tree were still closed. We also found larvae searching for food in the herbal layer without finding suitable plants. In some areas, larvae have to wait for the buds of the ash tree to open. Our data suggest that conservation strategies for E. maturna must be site specific according to food plant use of pre- and post-hibernation larvae and habitat type.  相似文献   

6.
In just a few years, the Asian fly Drosophila suzukii has invaded several continents and has become a very serious pest of many fruit crops worldwide. Current control methods rely on chemical insecticides or expensive and labour‐intensive cultural practices. Classical biological control through the introduction of Asian parasitoids that have co‐evolved with the pest may provide a sustainable solution on condition that they are sufficiently specific to avoid non‐target effects on local biodiversity. Here, we present the first study on the development of three larval parasitoids from China and Japan, the Braconidae Asobara japonica and the Figitidae Leptopilina japonica and Ganaspis sp., on D. suzukii. The Asian parasitoids were compared with Leptopilina heterotoma, a common parasitoid of several Drosophilidae worldwide. The three Asian species were successfully reared on D. suzukii larvae in both, blueberry and artificial diet, in contrast to L. heterotoma whose eggs and larvae were encapsulated by the host larvae. All parasitoids were able to oviposit one day after emergence. Asobara japonica laid as many eggs in larvae feeding in blueberry as in artificial diet, whereas L. heterotoma oviposited more in larvae on the artificial diet and the Asian Figitidae oviposited more in larvae feeding on blueberry. Ganaspis sp. laid very few eggs in larvae in the artificial diet, suggesting that it may be specialized in Drosophila species living in fresh fruits. These data will be used for the development of a host range testing to assess the suitability of Asian parasitoids as biological control agents in invaded regions.  相似文献   

7.
We investigated patterns of winter feeding tree choice in 4 groups of Sichuan snub-nosed monkeys (Rhinopithecus roxellanae) in Shennongjia Nature Reserve, China. We collected data during 2 winters from 1998 to 2000. The monkeys used mature forest, young forest and shrub forest, but not grassland. Groups used tree species in a significantly nonrandom pattern. There was a similar composition of preferred tree species between different habitats for each group and among the same habitat types for different groups. They preferred Abies fargesii, Pinus armandii and Salix walliciana for foraging. The 3 species occur in varying degrees of abundance in different habitats and were used differently by the 4 groups. The difference is probably due to interhabitat differences in availability of tree species, in addition to microclimate. The mean circumference of a tree had little effect on its preference score, but preferred species tend to be larger. A Wilcoxon signed-rank test indicated that the percentage of trees used and average number of feeding bites per tree is significantly greater for larger trees. For all trees in a given habitat, the percentage of trees used and average number of bites per tree have a significant positive correlation with average tree circumference. Our results indicate that Rhinopithecus roxellanae prefer to feed in large trees more than small trees in a given habitat, thereby preferring mature forest habitat. There is also a group-size effect; larger groups used higher-quality habitats than those of smaller groups. Both tree species and size are the major determinants of feeding choice, but tree species is more important than tree size. Our results have at least three implications for winter habitat conservation of Sichuan snub-nosed monkeys. Conservation efforts should be focused on mature forest because it is better habitat at Rhinopithecus than young forest, as long as the same tree species are present. Secondly, Pinus armandii, Abies fargesii and Salix walliciana should be conserved as top priority in forest communities. Third, the largest trees in each habitat should be given greatest possible protection.  相似文献   

8.
Environmental disturbances such as deforestation, urbanization or pollution have been widely acknowledged to play a key role in the emergence of many infectious diseases, including mosquito-borne viruses. However, we have little understanding of how habitat isolation affects the communities containing disease vectors. Here, we test the effects of habitat type and isolation on the colonization rates, species richness and abundances of mosquitoes and their aquatic predators in water-filled containers in northwestern Thailand. For eight weeks water-filled containers were monitored in areas containing forest, urban and agricultural habitats and mixtures of these three. Mosquito larvae of the genera Aedes and Culex appeared to be differentially affected by the presence of the dominant predator; Toxorhynchites splendens (Culicidae). Therefore, a predation experiment was conducted to determine predator response to prey density and its relative effects on different mosquito prey populations. Colonization rates, species richness and abundances of mosquito predators were strongly related to forest habitat and to the distance from other aquatic habitats. Areas with more tree cover had higher predator species richness and abundance in containers. Containers that were close to surface water were more rapidly colonized than those further away. In all habitat types, including urban areas, when predators were present, the number of mosquito larvae was much lower. Containers in urban areas closer to water-bodies, or with more canopy cover, had higher predator colonization rates and species richness. T. splendens (Culicidae) preyed on the larvae of two mosquito genera at different rates, which appeared to be related to prey behaviour. This study shows that anthropogenic landscape modification has an important effect on the natural biological control of mosquitoes. Vector control programmes and urban planning should attempt to integrate ecological theory when developing strategies to reduce mosquito populations. This would result in management strategies that are beneficial for both public health and biodiversity.  相似文献   

9.
1. Although numerous studies have examined the ecology of plant resistance to herbivores and the distribution of herbivores within plant hybrid zones, few have examined how plant hybridization influences herbivore growth, development, or life history. The experiment reported here examines variation in survivorship, development time, and final adult body size of Stator limbatus reared on seeds of parental and hybrid Cercidium floridum-×-C. microphyllum trees from a paloverde hybrid zone in eastern California. Because S. limbatus exhibits egg size plasticity in response to host species, the size of eggs that females lay on hybrid and parental plants is also examined. 2. The hypotheses (a) that seeds of hybrid trees are intermediate between those of the two parental species in their resistance to penetration by S. limbatus larvae; (b) that seeds of hybrid trees are intermediate in their suitability for the growth of larvae that successfully penetrate the seed-coat; (c) that female S. limbatus can distinguish between hybrid trees and pure-bred trees, as quantified by the size of eggs they lay on seeds of each taxon, and (d) that female S. limbatus can distinguish among individual hybrid trees, are tested. 3. On average, S. limbatus survivorship was lower, development time longer, and emergence body mass lower on seeds of C. floridum than on seeds of C. microphyllum. Seeds of hybrid trees were, on average (across trees), intermediate between seeds of the parental species in the resistance of their seed-coats to penetration by S. limbatus larvae and in their suitability for larval growth. Individual hybrid trees also varied in the resistance of their seeds to, and the suitability of their seeds for, S. limbatus larvae. 4. Female S. limbatus laid significantly larger eggs on seeds of C. floridum than on seeds of C. microphyllum, and, on average, intermediate size eggs on hybrid trees. The size of eggs laid by females also varied among hybrid trees, with females laying C. floridum-sized eggs on some trees, and C. microphyllum-sized eggs on other trees. These results suggest that females have at least some ability to distinguish among hybrid trees, but there was no evidence that females laid larger eggs on poorer quality hybrid trees.  相似文献   

10.
萧氏松茎象的生活史、产卵和取食习性   总被引:39,自引:0,他引:39       下载免费PDF全文
萧氏松茎象Hylobitelus xiaoi是严重蛀害国外松的新害虫。在江西赣南地区两年发生一代,以幼虫在蛀道、成虫在蛹室或土中越冬。卵和蛹的发育起点温度分别为8.4℃和7.5℃,有效积温分别为215.9和345.3日·度。各虫态历期:13~28℃间,卵为52.9~11.4天;13~30℃间,蛹为60.1~16.4天; 25℃恒温下,幼虫128.9天。成虫靠爬行活动,极少飞翔。成虫具夜出性活动节律:即傍晚上树行取食、交配和扩散等活动,早晨回到树干基部或土缝中。成虫需取食松枝作为补充营养,产卵前期46.3天,产卵期 105.3天,卵产于近表土的寄主树皮内,每雌产卵35.7粒。幼虫5~7龄,以幼树危害最烈。  相似文献   

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