Impact of Two Accidentally Introduced Encarsia Species (Hymenoptera: Aphelinidae) and Other Biotic and Abiotic Factors on the Spiralling Whitefly Aleurodicus dispersus (Russell) (Homoptera: Aleyrodidae), in Benin, West Africa

In early 1993, the spiralling whitefly, Aleurodicus dispersus (Russell), was observed in Benin for the first time, inflicting damage to ornamental and shade trees and cassava. The parasitoids Encarsia ?haitiensis Dozier and E. guadeloupae Viggiani were observed in the second half of 1993. They were known to have the same host in the Pacific region, and were thought to have been introduced accidentally. The impact of these parasitoids was quantified using four surveys from 1993 to 1995 (on 2541 trees in 537 localities) and by population studies on guava. In 1993, A. dispersus occurred mostly in towns in the southern part of Benin; penetration into farmland was observed later. E. ?haitiensis was more abundant and widespread than E. guadeloupae , and by 1995 it had been recovered from most (84%) of the infested localities. On guava trees, the annual peaks of A. dispersus population declined by ca. 80% between 1993 and 1996. During the same period parasitism rates increased. Econometric multiple regression analyses based on 996 infested trees demonstrated that A. dispersus population densities, the proportion of infested trees and damage scores all declined significantly with increasing duration of the presence of the parasitoids, indicating their impact. Other variables were also significantly related to A. dispersus levels.     

地形因子对黄土高原山杏叶片功能性状的影响

坡向和坡度是重要的地形因子,调控水、热组合可以影响植物生长及叶片功能性状,研究叶片功能性状对不同地形因子的响应,有助于了解植物对环境的适应策略.以阳坡(半阳坡)和阴坡(半阴坡)2个坡向,以及15°~20°、21°~25°和26°~30°3个坡度为环境梯度,对比研究了其对黄土高原主要造林树种山杏叶片功能性状(包括叶面积、比叶面积、叶干物质含量和叶片含水量)的影响,结果表明:1)坡向与坡度分别对所有叶片功能性状的影响均显著,坡向和坡度仅对叶片含水量具有交互作用.2)坡向梯度上,阳坡叶片的叶面积与阴坡相当,但叶干物质含量(0.24 g·g^-1)和叶片含水量(59.6%)均小于后者(0.27 g·g^-1和67.0%);阳坡叶片的比叶面积显著高于阴坡,其值分别为183.72和163.05 cm2·g^-1.3)坡度梯度上,叶片的比叶面积和叶面积均随坡度增大呈先减后增趋势,二者分别在15°~20°和26°~30°上达最大值,分别为184.04 cm^2·g^-1和21.14 cm2.4)除15°~20°与26°~30°的土壤水分无差异外,其余坡度以及坡向之间的土壤水分均存在显著差异,且土壤水分是造成叶片功能性状差异的主要原因之一,其中0~10 cm土层含水量对叶片功能性状的影响最大.5)叶片比叶面积与叶片含水量、叶干物质含量呈负相关,与叶面积呈正相关;叶干物质含量与叶片含水量呈正相关,与叶面积呈负相关;土壤含水量仅与叶片含水量呈正相关,与其他叶片功能性状均不相关.     

不同林龄刺槐叶功能性状差异及其与土壤养分的关系

对不同林龄刺槐群落叶功能性状差异及其与土壤养分的关系进行研究,分析刺槐对黄土丘陵区土壤环境的适应策略.结果表明: 随林龄的增大,刺槐比叶面积、叶面积、叶片含水量、叶全氮含量及叶有机碳含量呈先增大后减小的变化趋势,且在30年林龄时达到最大值,分别为279.18 cm²·g^-1、12.33 cm²、0.09%、33.01 g·kg^-1、523.08 g·kg^-1.随林龄的增大,叶组织密度、叶全磷含量、叶厚度及气孔密度呈增大趋势,气孔长度及气孔宽度呈减小趋势.主成分分析表明,叶面积、比叶面积、叶全磷含量、叶片含水量、叶厚度及气孔密度均为刺槐叶功能性状随林龄变化的主要指标.各指标间呈一定的相关性,这表明刺槐能改变自身的形态结构,形成最佳功能组合以适应环境的变化.影响叶面积、叶片含水量、比叶面积及气孔长度的主要土壤因子是土壤全氮含量,影响气孔宽度、叶组织密度、叶厚度、叶全磷含量、叶全氮含量及气孔密度的主要土壤因子是土壤有机碳含量,这表明土壤全氮含量和有机碳含量是影响不同林龄刺槐叶功能性状的主要土壤因子.随林龄的增大,刺槐群落土壤养分得到改善,进而影响刺槐叶功能性状.不同林龄刺槐叶功能性状的差异反映出刺槐具有较强的叶片形态可塑性,有利于其适应黄土丘陵区的土壤环境.     

The survival, growth and diet of pike fry, Esox lucius L., stocked at different densities in experimental ponds

Yolk-sac pike fry were stocked at densities of 0.74 – 81.4 m⁻² in two ponds, each divided into eight sectors (mean area 155.8 m²). Growth and survival were recorded from May to December 1985. The growth rates were variable within each sector. The size-range of sampled fish increased throughout the year, but showed no significant correlation with density. Fry survival was initially density-independent but switched by late June/July to density-dependence, ranging from 0.5 to 43.6% of initial stocking numbers. The highest mean daily mortality rates occurred during May-July. The final survival in December ranged between sectors from 0.059 to 11.25% of the starting stock densities. The final biomass per unit area of pike surviving in December was not related to initial stocking density. In Pond 1 the mean biomass produced was 2.21 gm⁻² and in Pond 2 was 3.49gm⁻².
Pike fry < 30 mm fed only on invertebrates; those 30–100 mm took a wide range of invertebrates, cyprinids. sticklebacks and other pike. Cannibalism occurred at most densities between 5.45 and 81.4 fish m⁻².
Where attempts are made to increase pike production in managed populations by releasing small fry, an upper stock density of 5 fry m⁻² is advised if large, density-dependent mortalities are to be avoided.     

Natural history of whitefly in Costa Rica: an evolutionary starting point

Abstract.  1. To understand evolution of foraging behaviour in the whitefly parasitoid Encarsia formosa (Hymenoptera, Aphelinidae), natural densities and distributions of whitefly (Homoptera, Aleyrodidae) were quantified in E. formosa 's presumed area of origin, the Neotropics.
2. Leaves were collected in Costa Rican nature areas along long transects (2–4 km), short transects (100 m), within 3-D plots (50 dm³−2.3 m³) and along suspension bridges within the canopy, and checked for presence of whitefly nymphs.
3. Generalised linear mixed modelling revealed that the number of hosts on the lower side of a leaflet of an average plant within an average spot of an average transect could be described by a Poisson distribution with mean and variance equal to 0.241, in a ratio of I1:I2:I3:I4 = 0.14:0.23:0.26:0.37. The Poisson mean was affected largely by the plant and less by the spot or transect. Variation in leaf area explained little of the variation between plants. Based on the shape of the opening in vacated puparia, the probability that a whitefly became parasitised eventually was 12% on an average leaflet. Whitefly density was much lower in the canopy than at the forest floor in the same area.
4. Semivariance analyses showed that in one of the three short transects, the numbers of whiteflies on leaves were spatially dependent. In four of seven 3-D plots at least one level of spatial dependence could be detected.
5. Results are discussed in the context of understanding evolution of foraging behaviour by E. formosa .     

红树林植物叶片形态和解剖特征对叶肉导度、叶片导水率的影响

叶肉导度和叶片导水率是影响光合作用的两个重要过程,叶肉导度通过影响从气孔下腔到Rubisco酶位点的二氧化碳浓度梯度直接影响光合作用,而叶片导水率则通过影响水分供应或气孔行为来影响光合作用,然而对这两个生理过程之间的协同性研究较少。本研究选择9种红树林植物为研究对象,探讨盐生环境下植物叶肉导度和叶片导水率的协同性及其与叶片解剖结构特征之间的相关性。结果表明,9种红树林植物叶片导水率(0.78~5.83 mmol·m~(-2)·s~(-1)·MPa-1)、叶肉导度(0.06~0.36 mol·m~(-2)·s~(-1))、最大光合速率(7.23~23.71μmol·m~(-2)·s~(-1))等特征的差别较大;叶肉导度与最大光合速率呈显著正相关,而与比叶重无显著相关性,其原因是由于比叶重与叶片厚度、叶片密度不存在相关性;叶脉密度与气孔密度呈较强的相关性,说明红树林植物叶片水分运输与散失相关的叶片结构之间存在协同关系;叶片导水率不受叶脉密度影响,并且与叶肉导度、最大光合速率也不存在相关性,这很可能与红树林植物叶片的肉质化、有发达的储水组织有关,体现了红树林植物叶片结构和功能的特殊性。     

Does natural larval parasitism of Lobesia botrana (Lepidoptera: Tortricidae) vary between years, generation, density of the host and vine cultivar?

Populations of European grapevine moth Lobesia botrana Denis & Schiffermüller and its larval parasitoids were studied for two consecutive years on an experimental insecticide-free vineyard in France planted with adjacent plots of five grape cultivars (Merlot, Cabernet Franc, Sauvignon, Cabernet Sauvignon and Sémillon) using a natural L. botrana population during the first year, and a natural population supplemented with artificially inoculated individuals during the second year. Levels of natural populations of larval parasitoids were measured by their parasitism rate. The ichneumonid Campoplex capitator Aubert was the most common species collected from L. botrana larvae. Its incidence was higher during the spring compared to summer. The overall parasitism rate found on the experimental vineyard varied from 23% in 2000 to 53% in 2001, and was mainly due to C. capitator. Parasitism was not affected by the grape cultivar on which the host developed but was positively correlated with the host density, per bunch or per stock, suggesting that among the five grape cultivars tested, C. capitator females probably do not discriminate between hosts feeding on different grape cultivars, but rather the densities of L. botrana larvae.     

Relationships between photosynthesis, nitrogen and leaf structure in 14 grass species and their dependence on the basis of expression

The relationships between leaf structure, nitrogen concentration and CO₂ assimilation rate ( A ) were studied for 14 grass species grown in the laboratory under non-limiting nutrient conditions. Structural features included leaf thickness and density, and the proportion of leaf volume occupied by different types of tissue (mesophyll, epidermis, vessels and sclerenchyma). Relationships were assessed for data expressed per unit leaf area and fresh mass. The latter was found to be closely related to leaf volume, which allowed us to use A per unit leaf fresh mass ( A _fm) as a surrogate of A per unit leaf volume. Assimilation rate per unit leaf area ( A _a) was positively correlated with leaf thickness and with the amount of mesophyll per unit leaf area; the relationship with leaf nitrogen content per unit area was only marginally significant. A _fm was negatively correlated with leaf thickness and positively with fresh mass-based leaf organic nitrogen concentration. A multiple regression involving these two variables explained 81% of the variance in A _fm. The value of A _fm was also significantly related to the proportion of mesophyll in the leaf volume, but surprisingly the correlation was negative. This was because thin leaves with high A _fm and nitrogen concentration had proportionally more mechanically supportive tissues than thick ones; as a consequence, they also had a lower proportion of mesophyll. These data suggest that, in addition to leaf nitrogen, leaf thickness has a strong impact on CO₂ assimilation rate for the grass species studied.     

Photosynthetic response of Eragrostis tef to temperature

Photosynthetic characteristics of leaves of tef, Eragrostis tef (Zucc.) Trotter, plants, grown at 25/15°C (day/night), were measured at temperatures from 18 to 48°C. The highest carbon exchange rates (CER) occurred between 36 and 42°C. and averaged 27 μmol m⁻² s⁻¹. At lower or higher temperatures, CER was reduced, but the availability of CO₂ to the mesophyll, measured as internal CO₂ concentration, was highest when temperatures were above or below the optimum for CER. In addition, CER and stomatal conductance were not correlated, but residual conductance was highly correlated with CER (r = 0.98). In additional experiments, relative ¹³C composition for leaf tissue grown at 25, 35 and 45°C averaged -14.4 per mille, confirming that tef is a C₄ grass species. Dry matter accumulation was higher at 35 than at 25, and lowest at 45°C. Leaf CER rates increased hyperbolically with increased light when measured from 0 to 2000 μmol m⁻² s⁻¹ PPFD. The highest CER, 31.8 μ-mol m_-2 s⁻¹, occurred at 35°C and 2000 μmol m⁻² s⁻¹ PPFR. At high light, CER at 25 and 35°C were nearly equal because of higher stomatal conductance at 25°C. Residual conductance was, however, clearly highest at 35°C compared to 25 and 45°C treatments. Stomatal conductance and residual conductance were not correlated in either set of experiments, yet residual conductance was always highest when temperatures were between 35 and 42°C across experiments, suggesting that internal leaf photosynthetic potential was highest across that temperature range.     

华西雨屏区麻栎-喜树人工混交林林冠对降雨中钾和钠离子再分配的影响

2016年12月—2017年11月研究了都江堰灵岩山麻栎-喜树人工混交林林冠对不同物候期(无叶期、展叶期、盛叶期和落叶期)雨水中K⁺和Na⁺的再分配作用.结果表明: 大气降雨中K⁺和Na⁺浓度分别为1.87和1.46 mg·L^-1,穿透雨中分别为5.78和1.39 mg·L^-1,雨水中的K⁺浓度在展叶期最高,盛叶期最低,Na⁺在无叶期和展叶期较高,盛叶期和落叶期较低;大气降雨中K⁺和Na⁺的输入量分别为25.47和21.60 kg·hm^-2·a^-1;降雨对林冠中K⁺的淋溶量为13.64 kg·hm^-2·a^-1,无叶期、展叶期、盛叶期和落叶期的淋溶量分别为1.67、6.23、2.28和3.46 kg·hm^-2,在展叶期淋溶量最大;林冠对Na⁺的截留量为11.26 kg·hm^-2·a^-1,无叶期、展叶期、盛叶期和落叶期的截留率分别为32.6%、18.0%、44.9%和31.5%,盛叶期时截留量最大.可见,麻栎-喜树人工混交林林冠对大气降雨中K⁺和Na⁺的再分配作用随物候期而变化,这为深入了解华西雨屏区森林生态系统的K⁺和Na⁺循环提供了基础数据.     

Short-term thermal acclimation induces adaptive changes in the inner mitochondrial membranes of fish skeletal muscle

In the oxidative muscles (musculi laterales superficiales) of crucian carp Carassius carassius acclimated for 6 weeks to either 5 or 25° C, the volume density and the surface density of fibres per tissue did not differ significantly between the control and experimental groups. The correlation ratio (μ²) for these values was below 50, 39·3 and 43·9 respectively. After acclimation to 5° C, the surface density of outer mitochondrial membrane per fibre increased significantly from 0·93 to 1·23m² cm⁻³ in the summer population but dropped from 0·94 to 0·67 m² cm⁻³ in the winter population. The surface density of outer mitochondrial membrane per mitochondrion increased from 3·24 to 4·52 m² cm⁻³ in summer fish. After acclimation to 25° C, the surface density of inner mitochondrial membranes per muscle fibre decreased from 4·04 to 1·79 m² cm⁻³ in summer fish and from 3·86 to 1·07 m² cm⁻³ in winter fish. The surface density of inner mitochondrial membranes per mitochondrion increased from 14·17 to 15·60 m²cm⁻³ in summer fish but dropped from 13·91 to 10·67 m² cm⁻³ in winter fish. Correlation matrices demonstrate a negative correlation of the surface density of outer mitochondrial membrane per mitochondrion with the volume density of mitochondria per fibre and temperature, suggesting cold-induced proliferation of small mitochondria. It was concluded that short-term cold acclimation increased surface area of the inner mitochondrial membranes in summer fish.     

Mating and host density affect host feeding and parasitism in two species of whitefly parasitoids

Abstract The parasitoids in the genera of Encarsia and Eretmocerus (Hymenoptera: Aphelinidae) are important biological control agents of whiteflies, and some of them not only parasitize hosts but also kill them with strong host‐feeding capacity. Two whitefly parasitoid species, Encarsia sophia and Eretmocerus melanoscutus were examined to determine if mating and host density affected their host feeding and parasitism. The whitefly host, Bemisia tabaci, was presented to these two wasp species in densities of 10, 20, 30, 40, 50 and 60 third‐instar nymphs per clip cage. Mated whitefly parasitoid females fed on more hosts than unmated females under a range of host densities (under all six host densities for En. sophia; under the densities of 40 nymphs or more for Er. melanoscutus). Meanwhile, mated females parasitized more whitefly nymphs than unmated females under all host densities for both species. With increase of host density, mated or unmated Er. melanoscutus females killed more hosts by host feeding and parasitism. Mated En. sophia females killed more hosts by host feeding with increase of host density, whereas unmated females did not parasitze whitefly nymphs at all. Our results suggest that only mated female parasitoids with host‐feeding behavior should be released in crop systems to increase their bio‐control efficiency.     

Role of sodium in the ABA‐mediated long‐term growth response of bean to salt stress

Long‐term salt effects on plant growth have often been related to direct ion toxicity due to the accumulation of high ion concentrations in plant tissue. This work examines the relative importance of endogenous ABA, as well as Na⁺ and Cl⁻ toxicity, in the inhibition of leaf growth and photosynthesis, in bean plants grown at 1, 25, 50 and 75 m M NaCl until the fruit‐bearing stage. All salt‐treated plants showed very high leaf Cl⁻ concentrations, with little difference between plants exposed to 50 or 75 m M NaCl. The 25 and 50 mM salt‐treated plants were able to successfully exclude Na⁺ from their leaves, and only suffered an initial decline in the rate of leaf growth. Plants exposed to 75 m M NaCl showed an increase in Na⁺ leaf concentrations with an accompanying decrease in growth and photosynthesis as salt exposure progressed. A high correlation was found between leaf Na⁺ and leaf growth. Leaf ABA significantly increased with salt supply, and was highly correlated with both leaf Na⁺ and leaf growth. Our results suggest that in bean plants under long‐term salt stress, leaf ABA may participate in the regulation of leaf growth, and leaf Na⁺ would be at least partly responsible for increased ABA levels.     

Population ecology of the paddy field-dwelling fish Channa gachua (Günther) (Perciformes, Channidae) in Sri Lanka

A population of Channa gachua in a small irrigation canal that supplies rice fields was studied by monthly sampling over 2 years. The population density was positively correlated with the rainfall and varied from 0.34 to 0.95 individuals m⁻². The growth parameters of the von Bertalanffy growth equation determined on monthly size–frequency data were L_x = 179 mm total length and K =0.50. Overall male to female ratio was 0.82 and there were more females than males in the middle size classes. Spawning occurred throughout the year, but all evidence indicated enhanced breeding during major rainy periods of May to July and October to December. The length at first spawning was 102 mm, which is reached in about 20 months. Fecundity, which varied between 389 and 2130, was positively correlated with gonad weight, body weight and total length. Longevity and natural mortality were estimated as 6 years and l.27 yr⁻¹, respectively. However, 99% of the population appeared to live for only 3 years. The mean biomass, average annual production and turnover ratio of the population were 7.35 g m⁻², 12.06 g m⁻² and 1.64, respectively.     

Factors affecting the biological control of the spiralling whitefly Aleurodicus dispersus (Hemiptera: Aleyrodidae) in banana plantations in Costa Rica: a study case

ABSTRACT

A study was conducted to reveal the causes for Aleurodicus dispersus outbreak in commercial banana plantations in Costa Rica. Biotic and abiotic factors affecting the abundance of the spiralling whitefly were determined. Four nymph parasitoids and nine predators were found to affect A. dispersus population. Seventeen families of host plants for A. dispersus in the banana area were identified, allowing the whitefly to reach a high reproductive and dispersal rate and pest status in short periods. The use of nematicides during the dry season was the key factor for mortality of natural enemies responsible for maintaining pest populations under economic levels.     

西大明山自然保护区冠斑犀鸟的分布及保护现状

采用点计数调查法和访问方法在2004年12月、2005年10月、2006年4月、2006年12月及2007年5月对西大明山自然保护区的三大林区(即:凤凰山林区、西大明山林区和小明山林区)冠斑犀鸟(Anthracoceros albirostris)的数量及分布情况进行了系统调查.结果显示,西大明山自然保护区的种群数量约53±8只,按保护区的面积计算种群密度为0.088ind·km²,按森林覆盖面积为0.23ind·km².其中:凤凰山林区及西大明山林区估算冠斑犀鸟有41±5只,比2000年数据减少了约30只;小明山林区仅剩12只.结果反映西大明山自然保护区的冠斑犀鸟已处在极度濒危的边缘.     

生活污水慢渗对‘中林2001’杨树人工林生长的影响

采用不同污水水力负荷(每周0、3、6、9、12、15 cm),在‘中林2001’杨树人工林林地进行了污水慢渗试验.结果表明：不同负荷生活污水处理使‘中林2001’杨树人工林土壤平均有机质、全氮、全磷、全钾和Na⁺含量分别比对照(0 cm)增加1.940、0.115、0.029、1.454和0.030 g·kg^-1;在较低水力负荷(3～12 cm)时,杨树平均总生长量增加17.583 t·hm^-2·a^-1,各器官的平均氮、磷、Na⁺含量分别增加3.086、0.645和0.121 g·kg^-1,水力负荷在每周6～12 cm时, 杨树平均总生长量和各器官平均氮、磷、Na⁺含量达到最大值(36.252 t·hm^-2·a^-1、13.162 g·kg^-1、5.137 g·kg^-1、0.361 g·kg^-1),负荷继续升高则有所下降.杨树各器官钾含量随着水力负荷的增加而降低;污水处理使杨树的叶长增加,叶不对称性减少、使林木延迟落叶.当水力负荷＞每周12 cm时,土壤中较高的Na⁺和水分含量将危害杨树生长.适宜‘中林2001’杨树人工林生长的污水水力负荷在每周3～12 cm.     

38个榛种质资源叶功能性状与光合特征变异及其相关性

研究了38个榛种质资源叶功能性状与光合特征参数的变异特征及其相关关系,为优良种质资源的选择以及进一步理解叶功能性状对光合特征的影响机制提供科学依据。结果表明:38个种质资源的叶面积(LA)、叶形指数(LI)、叶干重(LDW)、比叶面积(SLA)和叶干物质含量(LDMC)平均值分别为78.39 cm²、1.24、0.73 g、109.95 cm²·g^-1和38.31%,LDW变异最大,其次为LA和SLA,LI和LDMC变异最小;净光合速率(Pn)、蒸腾速率(Tr)、气孔导度(gs)、胞间CO2浓度(Ci)、气孔限制值(Ls)和水分利用效率(WUE)平均值分别为9.92μmol·m^-2·s^-1、3.88 mmol·m^-2·s^-1、153.04μmol·m^-2·s^-1、238.73μmol·mol^-1、0.41和2.54μmol·mmol-1,gs变异最大(27.89%),Pn、Ci、Ls和WUE次之(10.37%~15.14%),Tr最小(9.99%)。不同种质资源叶功能性状与光合特征参数之间均存在极显著差异。Pearson相关分析表明:Pn与LA、LDW、LDMC均呈显著正相关,与SLA则呈显著负相关;Tr与LA呈显著正相关;gs和Ci与LDMC分别呈显著负相关和正相关;WUE与LDW、LDMC均呈显著正相关,与SLA则呈显著负相关。冗余分析表明:第1、2排序轴共同解释了叶片光合特征总变异的88.6%,其中,对光合特征产生显著影响的叶功能性状因子为SLA和LDMC。平欧210号、F-03、平欧11号、平欧88号、平欧119号、85-162、平欧48号、玉坠、平欧110号表现出较高的水分和光能利用效率。     

A hierarchical multi‐scale analysis of the spatial relationship between parasitism and host density in urban habitats

Studies on spatial density dependence in parasitism have paid scarce attention to how changes in host density at different hierarchical scales could influence parasitism in an herbivore at a particular scale. Here, we evaluated if rates of parasitism per leaf (by the whole parasitic complex and by dominant species) of the specialist leaf miner Liriomyza commelinae (Diptera: Agromyzidae) respond to variations in host density at the leaf, plant patch and site levels in an urban setting. We used multi‐level Bayesian models that incorporate the spatial hierarchy occurring in this system, as well as habitat factors previously found to have an effect on the L. commelinae parasitoid community in an urban context (patch size, patch isolation and urbanization level). According to the fitted model, overall parasitism rates decreased with increasing number of mines per leaf, being independent of host‐density variations at patch and site level. Patch structure was found to have a strong effect on parasitism rates per leaf. The analysis of parasitism by parasitoid species separately showed consistent results with the response at community level. These results suggest that parasitism of the parasitoid community here studied would be sensitive to hierarchical cues related to the host at the leaf level and to the host habitat at the patch level.