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1.
We monitored winter cereal fields in a Mediterranean arable crop system to obtain information about the aphid parasitoid species composition and the aphid–parasitoid interactions through the whole cropping cycle. Nine species of aphid primary parasitoids (Hymenoptera, Braconidae, Aphidiinae) were identified. The most abundant species were Aphidius rhopalosiphi, Aphidius matricariae, Aphidius ervi and Lysiphlebus testaceipes. The genus Aphelinus sp. (Hym., Aphelinidae) was also identified. We determined seasonal host–parasitoid associations over the entire cereal crop cycle. A number of new such associations were recorded, which were previously unknown in Spain and Europe. Our results indicated broad associations of L. testaceipes and A. matricariae with cereal aphids; furthermore, the association of Aphelinus sp. with several cereal aphid species was also substantial. In the NE of the Iberian Peninsula, the cereal aphid parasitoids that we identified are able to develop throughout the crop season on one or more host species. Thus, the main aphid species can be parasitized effectively throughout the entire cereal crop cycle. We discuss the role of cereal aphid parasitoids in the region in the context of our experimental results.  相似文献   

2.
Studies conducted in the 2000 cropping season at two different localities, Flaeming and Magdeburger Boerde in Germany, have provided new information on cereal aphid (Sitobion avenae (F.), Metopolophium dirhodum (Walker), and Rhopalosiphum padi (L.)) parasitoids in winter wheat; their species composition, relative abundance, hosts, and location effects. The average aphid population density was higher at Magdeburger Boerde and lower at Flaeming. Among the aphid species, Sitobion avenae was more abundant at Flaeming and Metopolophium dirhodum at Magdeburger Boerde. In total, eight species of primary parasitoids were recorded: Aphidius colemani Viereck, Aphidius rhopalosiphi DeStefani Perez, Aphidius uzbekistanicus Luzhetzki, Aphidius ervi Haliday, Aphidius picipes (Nees), Ephedrus plagiator (Nees), Praon gallicumStarý, and Praon volucre (Haliday). The predominant parasitoid species were Aphidius colemani and Aphidius rhopalosiphi on Metopolophium dirhodum and Aphidius uzbekistanicus on Sitobion avenae. A low number of hyperparasitoids were also recorded. Aphidius colemani was recorded for the first time in the open winter wheat fields in Germany, although it has been used as a biocontrol agent in glasshouses in many European countries and overseas. An analysis of the aforementioned information shows that Aphidius colemani detected as a parasitoid of cereal aphids in Germany is likely a result of an accidental escape of parasitoids from a glasshouse, as well as their successful overwintering and establishment in the area. This study provides baseline information essential for assessing future changes in aphid parasitoid species guild and dynamics in cereal fields in Germany.  相似文献   

3.
Bees and wasps provide important ecosystem services such as pollination and biocontrol in crop-dominated landscapes, but surprisingly little information is available on hymenopteran communities in temperate forest ecosystems. Species richness and abundance of bees and wasps can be hypothesised to increase with plant diversity, structural complexity, and availability of food and nesting resources. By experimentally exposing standardised nesting sites, we examined abundance and species richness of cavity-nesting bees (pollinators), wasps (predators) and their associated parasitoids across a tree diversity gradient in a temperate deciduous forest habitat. In addition, spatial distribution of individuals and species across forest strata (canopy vs. understory) was tested. Abundance and species richness was high for predatory wasps, but generally low for pollinators. Species-rich forest stands supported increased abundance, but not species richness, of pollinators and predatory wasps, and also increased abundance and species richness of natural enemies. In addition, the forests showed a distinct spatial stratification in that abundance of bees, wasps and parasitoids as well as parasitism rates were higher in the canopy than understory. We conclude that particularly the canopy in temperate forest stands can serve as an important habitat for predatory wasp species and natural enemies, but not bee pollinators. Enhanced tree diversity was related to increased hymenopteran abundance, which is likely to be linked to an increase in nesting and food resources in mixed forest stands.  相似文献   

4.
采用典型样方法,对武汉市10个具有代表性的城市公园的165个植物群落进行调查,结果表明,所调查植物群落中共有植物219种,分属74科156属;运用组平均法(UPGMA)对165个植物群落进行聚类分析,分为21种植物群落类型;利用Partrick物种丰富度指数、Shannon-Wiener多样性指数、Simpson多样性指数和Pielou均匀度指数,比较不同群落类型的物种多样性特征,其中群落类型紫玉兰-杜鹃-小苜蓿的物种丰富度和物种多样性最高,圆柏-八角金盘+山茶的物种丰富度最低,水杉-杜鹃+洒金桃叶珊瑚-早熟禾+车前的多样性指数最低,植物群落的多样性程度表现为乔木层 ≈ 草本层 > 灌木层。在城市公园绿地中人工配置决定了植物群落物种多样性特征,其他环境和人为干扰因素也影响植物群落的物种多样性。建议适当增加观赏价值高的乡土植物,构建物种丰富、层次复杂、结构稳定的近自然植物群落。  相似文献   

5.
The presence of a natural enemy in a habitat refuge is no guarantee of emigration by these into crop fields, when pest population outbreaks occur. Parasitoids from a refuge may not prefer foraging on the pest crop, exhibiting host fidelity, and therefore not constituting a source of natural enemies for improving biological control. An effective refuge must not only be a suitable sink for natural enemies, providing an acceptable host when these are not present in the crop, but it must also be a suitable source of parasitoids that readily accept the aphid-host on the crop. Therefore, crop-originated parasitoids would have to accept pests from the refuge as hosts to lay eggs in, and refuge-originated parasitoids would have to accept and lay eggs in pests from the crop. We here study the host fidelity of populations of Eriosoma lanigerum originating from two host plants (firethorn and apple) through reciprocal transfer experiments. Thereafter, the host fidelity of parasitoids from populations in the two host plants (firethorn and apple) was assessed. Reciprocal transfer experiments of parasitoids did not show an association between apple-originated parasitoids and their preference for any of the aphid hosts. Conversely, parasitoids from firethorn exhibited a higher number of attacks and in less time when aphids from apple were offered, suggesting a preference for apple-originated aphids. If future field work confirms these findings, firethorn could become an important management tool for enhancing biological control of woolly apple aphid in apple orchards, without being a substantial source of aphids.  相似文献   

6.
The vegetation of Pinus radiata plantation forests in New Zealand was studied to examine how the indigenous flora has responded to this novel habitat. A chronosequence of stands about 5, 16 and 27 years was assessed in each of four different biogeographic regions to test the effects of several stand and site factors on the succession of vascular understorey plant communities. A total of 202 indigenous and 70 adventive vascular plant species were found across all study areas, with considerable geographic variation among forests in species composition, species richness (range 48–135 species), and the percentage of indigenous species (50–86%). Both richness and cover of adventive species decreased significantly over time, whereas richness and cover of indigenous species was highest in the oldest stands, and overall species richness was lowest at mid-rotation. The guild composition changed from dominance of grasses and forbs in young stands to dominance of ferns and understorey trees in mature stands. These temporal changes were accompanied by a decrease in light-demanding pioneer species and an increase in shade tolerant, later seral species adapted to a forest environment. Measurements of the degree of canopy closure in stands with low or high stocking and modelling of temporal changes of canopy closure indicated that these understorey plant dynamics are influenced by changes in light availability as stands age. Despite the successional changes within forests, geographic variation more strongly influenced understorey communities because stands within a forest area were grouped together in DCA and TWINSPAN analyses, along rainfall and temperature gradients. Although the canopy species of such intensively managed plantation forests is an alien element in the New Zealand flora, the sheltered forest environment of older stands allows the establishment of a mostly indigenous forest understorey community with considerable similarities to indigenous forests located nearby.  相似文献   

7.
描述了埃塞俄比亚东南部Dello Menna森林植被的植物区系组成和植被结构。鉴定和描述了50个20m×20m的样方的植物群落类型、物种多样性、丰富度和均匀性,分析了已鉴定植物群落类型与环境因子的相关性,还描述了木本植物种群结构。每个样方内,均记录木本植物的物种、丰富度、高度和胸径以及海拔、坡度。利用PC-ORD软件对植被进行分类。用Sorensen相似性系数探测群落之间的差异性。计算Shannon-Wiener多样性指数、物种丰富度、Shannon均匀性来描述各种植物群落的物种多样性。共记录了53个科的171个维管植物种。豆科植物是主要的优势植物科系,包括13个属26种(1 5%),其次依次是菊科、唇形科和槭树科,各包括8个物种(4.6%)。根据植物分类结果,识别并描述了3个植物群落(Dalbergia microphylla群落、Grewia bicolar-Acaciabrevispica群落、Combretum molle-Combretum collinum群落)。植物区系之间的物种丰富度、多样性和均匀性存在差异。物种丰富度和多样性随海拔变化呈现出贝尔型分布。群落间植物随海拔梯度有一定的变化,表明海拔是决定植物群落分布的重要因素之一。Dalbergia microphylla群落物种丰富度和多样性均最高。优势种群落结构呈现出各种模型。植被可持续利用是今后的研究方向。  相似文献   

8.
Trees at low density and cereals may be combined in silvoarable agroforestry systems: tree rows and their companion vegetation introduce an heterogeneity in the cropped field that may modify the dynamics of insects crop pests and their predators. This hypothesis was tested in tree-wheat systems by monitoring aphids and their predators for two years in southern France, in two fields in 2006 and one in 2007. Tree row vegetation diversity was either suppressed by weeding or stimulated by seeding flowering species that could attract adult predators of aphids. The dynamics of aphids and predators were recorded by tiller sampling and yellow trap monitoring. Between 3500 and 5000 aphids were collected from each studied field. Surprisingly, no differences could be evidenced on the dynamics of both aphids and their predators between agroforestry and monocropping plots, nor between weeded and flowered plots. The heterogeneity induced by the tree row in the cropped field was probably not strong enough to alter the populations dynamics. A high landscape diversity in the area due to nearby forest patches and fallows may have blurred the impact of the tree lines. Different results may be expected in areas with lower biodiversity like cereal monocropping zones.  相似文献   

9.
大关县3种筇竹群落生物多样性研究   总被引：2，自引：0，他引：2  
对大关县乔木-筇竹群落、灌木-筇竹群落和筇竹-草本群落3种群落,采用二元属性数据测度方法进行了生物多样性的调查。结果表明:3种筇竹群落类型中以乔木-筇竹群落物种总种数(178种)为最多。各层次物种丰富度的顺序依次为,乔木-筇竹群落的物种丰富度为乔木层>草本层>灌木层;灌木-筇竹群落和筇竹-草本群落的物种丰富度一致,其物种丰富度顺序依次都为灌木层>草本层>乔木层。乔木-筇竹群落的乔木层的Shannon-Wiener(H’)指数最高,灌木-筇竹群落的灌木层和草本层的H’指数最高,筇竹-草本群落各层的H’指数都较低。灌木-筇竹群落与筇竹-草本群落在环境梯度上不同点之间的共有种最少,相似性最低,群落间的差异大,群落间物种替代速率较高。  相似文献   

10.
Savanna vegetation is characterized by high and variable ground layer species richness regulated by functional group interactions with fire regimes and canopy cover. Frequent fire selects for C4 grasses and prairie forbs in canopy openings and C3 graminoid species and shade-adapted forbs and shrubs in canopy shade. Frequent fire also maximizes heterogeneity in partial canopy cover and species richness across the full canopy gradient. However, few studies have linked fire induced change in tree canopy cover with groundlayer vegetation dynamics in relation to this model. In 1986 and in 2007, we measured canopy cover and sampled groundlayer vegetation in 1 m2 plots along 53 transects at the Tefft Savanna, a fire managed 197 ha eastern sand savanna with strong canopy cover and elevation gradients. We analyzed temporal change in canopy cover and groundlayer vegetation, correlating percent change in canopy cover with change in ground layer functional groups. After 20 years of burning at 3 fires/decade, elevation accounted for 62% of the variation in an NMS ordination of groundlayer vegetation. However, canopy cover, which averaged 24-86% in 2007, had a significant secondary effect on the ordination. Five vegetation types classified by TWINSPAN varied significantly in elevation and canopy cover. Woody vegetation comprised 8 of the 12 species with greatest niche breadths, and tended to predominant in woodland or forest, where tree cover averaged 50% or more. Forbs had greater richness in savanna, which averaged less than 30% canopy cover. The C3 sedge Carex pensylvanica was the dominant graminoid species under woodland canopy cover, and was co-dominant with the C4 grasses Andropogon scoparius and Sorghastrum nutans under savanna canopy cover. As in other savannas, N-fixing species sorted across shade and canopy openings, and heterogeneity among transects was maximized at mid-canopy cover. Over time, canopy cover decreased up to 50%, creating more open savanna conditions at mid to high elevations. This decrease was associated with a 20-100 % increase in species richness and was significantly correlated with increasing richness and cover of C4 grasses and summer flowering prairie and woodland forbs. These results support a canopy cover model of fire-maintained savanna vegetation, with greater abundance of C4 grasses and prairie forb species associated with lower canopy cover, greater heterogeneity at mid-canopy cover, and species richness maximized across the light gradient. They also indicate that decreasing canopy cover caused by repeated burning increases species richness and abundance of C4 and prairie forb species.  相似文献   

11.
Intensive forest management practices often disturb understory vegetation, and the recovery of these plant communities may depend on the type and severity of the disturbance. We examined the effects of stump removal and N-fertilization on understory plant communities and functional group (shrubs, graminoids, forbs, and introduced species) cover and diversity at five study areas in the Pacific Northwest of North America 24–28 years after treatment. Treatments at each study area included stumped and non-stumped controls as well as four levels of broadcast ammonium nitrate (0, 336, 672, and 1345 kg N ha−1) in all combinations. Stumping had significant effects on community composition at all sites, and several plant species were associated (p < 0.05) with either controls or stumped plots. Diversity of graminoids, forbs and introduced species increased in stumped areas region wide. Stumping reduced cover and diversity of shrubs at some sites. Cover of graminoids and forbs also increased in stumped plots at some study areas. Forbs like Viola sempervirens were often indicators of stump removal while shrubs such as Acer circinatum tended to be associated with non-stumped plots. N-fertilization affected community composition at only one study area, and had no effects on cover or richness of functional groups. Stump removal has lasting impacts on plant communities and may make them more vulnerable to colonization by introduced species.  相似文献   

12.
Management treatments involving multiple herbicide applications are standard procedure on most industrial pine plantation sites in the southern USA, raising concerns about biodiversity impairment. Management decisions impact not only plant communities but also the habitat potential they create for wildlife. We tested the effects of five intensities of stand establishment treatments on vegetation communities in loblolly pine plantations (n = 4) to age 5 in the Middle Coastal Plain (MCP) of Mississippi. Measurements were species richness, diversity, coverage, and community composition. Treatments were combinations of mechanical site preparation (MSP), chemical site preparation (CSP), and herbaceous weed control (HWC) both banded or broadcast for 1 or 2 years using the same herbicide mixtures. Tree richness and diversity were reduced by increasing treatment intensity; tree coverage, which included crop and non-crop trees, was less in moderate-intensity treatments. Vine richness and coverage were less in more intensive treatments, but 2 diversity indices differed on whether vine diversity was likewise affected. Richness and coverage of forbs and graminoids was lessened by broadcast HWC, with effects mostly limited to the year of application. Plant communities differed in all 5 years, with CSP acting as the primary factor for years 2–5. Early seral communities were favored by CSP, but broadcast HWC suppressed resulting herbaceous plants. Though CSP may somewhat reduce stand-level plant diversity, it may increase overall biodiversity within plantation-dominated landscapes by creating early succession plant communities that enhance wildlife habitat.  相似文献   

13.
The parasitoids (Hymenoptera, Braconidae, Aphidiinae) of the cowpea aphid, Aphis craccivora Koch, were investigated throughout two far distant provinces, Tehran and Sistan-Baluchestan. Colonies of the cowpea aphid were collected from different host plants and reared under laboratory conditions until the parasitoids emerged. The aphids were parasitized by an expected range of parasitoids. The species were Aphidius colemani Viereck, Lysiphlebus fabarum (Marshall), Lysiphlebus confusus Tremblay and Eady, Lysiphlebus testaceipes (Cresson), Binodoxys acalephae (Marshall), Binodoxys angelicae (Haliday), Praon volucre (Haliday) and Ephedrus persicae Froggatt. L. testaceipes is reported here for the first time in Iran. The most common species was L. fabarum followed by B. acalephae and L. confusus. A key is provided for identification and host plant associations are considered.  相似文献   

14.
黄河阶地植物群落演替及物种多样性研究   总被引：1，自引：0，他引：1  
河流不同阶地的地形和形成年代具有较大差异,对该地区的植物群落物种组成、多样性和生产力等群落结构和功能造成很大影响.以流经青藏高原玛曲段黄河的3级阶地为研究对象,调查了不同阶地对高寒草甸植物群落的影响.结果显示:1)3级阶地上的土壤水分状况不同;2)3级阶地上植物群落的物种丰富度、多度、多样性、均匀度都有相似的发展趋势,即第3级阶地＞第2级阶地＞第1级阶地(P＜0.01);3)第1级阶地的植物群落和第2级阶地的植物群落相似性较高,而第1级阶地和第3级阶地之间的植物群落差异性较大;4)第1级阶地和第2级阶地上植物群落的地上生物量没有显著差异,但都比第3级阶地上植物群落的地上生物量小(P＜0.05).  相似文献   

15.
The ocurrence of the different cereal aphids (Hom., Aphididae) in Northern German wheat growing areas 1974 and 1975 In July, 1974 and 1975,Macrosiphum avenae (F.) was the most common aphid on cereal fields in Northern German wheat growing areas.Rhopalosiphum padi (L.) was less abundant, whileMetopolophium dirhodum (Wlk.) was found very seldom.R. padi infested field edges only in most cases, while this was not true for all fields infested byM. avenae.  相似文献   

16.
Studies were conducted in cucumber fields to evaluate the standard and reduced dosage rates of 5 insecticides for control the cotton whiteflyBemisia tabaci (Genn.) and melon aphidAphis gossypii Glov. and effect of insecticide application on associated parasites and predators. Eggs of whitefly appeared to be less susceptibility to all treatments (max. 66% reduction) than larval and pupal stages. Populations of larval and pupal stages of whitefly were significantly reduced in all treated plots. For example (larvae on day 10 after treatment with ethiofencarb, diafenthiuron, and chlorpyrifos methyl 67, 50, and 68% pupae 68, 69, and 75%). Two aphelinid parasitoids,Eretmocerus mundus Mercet andProspaltella lutea Masi, were the most primary important parasitoids of the whitefly pupae in all test plots. Percent parasitism, in most treated plots, were slightly affected as a result of insecticide application. However, all tested insecticides and dosage rates caused severe suppression of emergence of adult parasitoids. Moreover, longevity of adult parasitoids were highly decreased. Populations of the melon aphid were extremely reduced, especially by ethiofencarb and diafenthiuron. Populations of predator species (Chrysopa carnea Steph.,Coccinella undecimpunctata Reiche andSyrphus spp.) were reduced in all treated plots. However, ethiofencarb applied at rates as low as 208.4g a.i./1001 provided equally effective aphid control and conserved numbers of insect predators in the treated plots. Also, the prothiofos and chlorpyrifos methyl applications at rates as low as 166.7 g a.i./1001 kept aphid numbers below than those in control and caused a smaller reduction in the combined populations of insect predators.  相似文献   

17.
Generalist arthropod predators are potential drivers of population dynamics in a wide variety of ecosystems but their feeding habits are often difficult to reveal as they are small, mobile, and live among dense vegetation or in soils. DNA-based gut-content analysis is a powerful tool that enables studies on arthropod predator–prey interactions. We studied lycosid spiders (Pardosa spp.) in agroecosystems to see if they consumed cereal aphids (Rhopalosiphum padi) and Collembolans at random, i.e., in proportion to their abundance in the field. We also tested if consumption of the target prey items was affected by the presence of alternative food. Spiders were captured in farmers’ fields and their gut-contents screened by PCR with R. padi and Collembola primers. On all sampling occasions, concurrent assessments of total prey availability were carried out. Spider predation rates on R. padi always exceeded 50 %. Spiders also tested positive for Collembola but to a lower and more varying degree. In general, Pardosa did not consume R. padi and Collembolans in relation to their abundance in the field. Aphid predation was much higher than expected whereas consumption of Collembolans was considerably lower. The presence of alternative prey influenced consumption of the aphid. It was concluded that prey consumption by Pardosa spiders generally cannot be assumed to simply mirror prey availability. The spatial distribution of the target prey needs to be considered as well as the abundance, composition, and nutritional content of potential alternative food items.  相似文献   

18.
Forested riparian buffers in California historically supported high levels of biodiversity, but human activities have degraded these ecosystems over much of their former range. This study examined plant communities, belowground biodiversity and indicators of multiple ecosystem functions of riparian areas across an agricultural landscape in the Sacramento Valley of California, USA. Plant, nematode and soil microbial communities and soil physical and chemical properties were studied along 50-m transects at 20 sites that represented the different land use, soil and vegetation types in the landscape. Riparian zones supported greater plant diversity and nearly twice as much total carbon (C) per hectare compared to adjacent land managed for agricultural uses, but had generally lower soil microbial and nematode diversity and abundance. When woody plant communities were present in the riparian zone, plant diversity and species richness were higher, and soil nitrate and plant-available phosphorus levels were lower. Belowground diversity and community structure, however, appeared to depend more on plant productivity (as inferred by vegetation cover) than plant diversity or species richness. Greater plant species richness, nematode food web structure, total microbial biomass, woody C storage and lower soil nitrate and phosphorus loading were correlated with higher visual riparian health assessment scores, offering the possibility of managing these riparian habitats to provide multiple ecosystem functions.  相似文献   

19.
In light of a recent increase in the aphid populations on young canola (Brassica napus) in autumn in Northwestern Europe, we carried out a survey of their parasitoid species during this season. The study was done in France from 1998 to 2001 using different sampling methods. Results highlighted the presence of two main species of Aphidiinae, Aphidius matricariae and Diaeretiella rapae (and to a lesser extent Aphidius ervi) on Myzus persicae, and of D. rapae on Brevicoryne brassicae. Nine other Aphidiinae species were found occasionally as well as some Aphelinidae parasitoids and hyperparasitoids. There was no difference in parasitoid species pattern between fields in Northern and Southern France. The principal parasitoid species found in the fields were reared in the laboratory to confirm their ability to develop on the canola aphids. Aphidius matricariae and D. rapae were reared successfully on M. persicae, but a low parasitism rate was obtained for A. ervi on this aphid. This study showed that A. matricariae and D. rapae could develop on aphids on canola and that they are present naturally in canola in autumn. However, the parasitism rate is low in autumn, so the options could be the use of these parasitoids in augmentative release biological control programs or in an IPM project on canola fields during this time of the year.  相似文献   

20.
Despite concern over a putative “global pollination crisis”, we still have an incomplete understanding of how bee communities respond to land-use change. I studied the responses of social stingless (or “meliponine”) bees (Hymenoptera: Apidae: Meliponini) to surrounding forest cover and floral resources in 35 sites in a largely deforested landscape in Costa Rica over three years, sampling bees with a standardized netting protocol. I recorded a diverse fauna of meliponines, comprised of 20 species and nine genera. I found that meliponine species richness and abundance are strongly related to forest cover, but not floral resource variables (blooming plant species richness and abundance). The effect of forest on meliponine abundance, but not diversity, disappeared when the most common meliponine species, Trigona fulviventris (which comprised ∼45% of sampled individuals), was excluded from analyses. Meliponine community composition, by contrast, was related most strongly to plant species richness, only weakly to forest cover, and not related to blooming plant abundance. This work differs from past work in the same landscape, which did not find evidence of changes in species richness or abundance of meliponines and forest-related variables (distance to forest or forest fragment size), but did find shifts toward meliponine-dominated communities near forests, especially larger ones. The larger true sample size (i.e. number of sample sites) of the present work likely improved the statistical power to detect these relationships. While meliponines are forest dependent, I recorded some species in the smallest forest fragments in the landscape, and as a group they respond strongly to overall forest cover in the landscape (i.e. including both small and large patches of forest). Both of these observations support arguments for preserving even small fragments of forest in agricultural landscapes. Given the ecological and economic importance of meliponine bees, it is imperative that we better understand their long-term conservation needs in the changing tropical landscapes of the world.  相似文献   

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