棉蚜获得黄瓜花叶病毒的行为与取食过程的关系

利用刺吸电位（EPG）及其即时中断技术研究了棉蚜Aphis gossypii传播黄瓜花叶病毒(CMV)的机理,分析电势落差波(pd)及其亚波形在棉蚜获得CMV的取食行为过程中的作用。结果表明：棉蚜的获毒需要pd波的发生,它的获毒效率与穿刺病株细胞膜的次数呈正相关。证明了这种行为是一种细胞内行为。对植物细胞内穿刺产生的电位落差（pd）波亚波形分析的结果显示,棉蚜的获毒发生在pd波的Ⅱ-3阶段,与棉蚜主动吸食植物细胞汁液的活动相关, 这支持了蚜虫获毒的 “吸入假说”。     

景观中心度及其在生态网络规划与管理中的应用

构建连续性生态网络已成为生物多样性保护、生态环境安全管理、游憩和历史文化资源保护的重要景观规划策略,其规划与管理已受到广泛关注.关键景观组分的识别是生态网络规划与管理的重点和难点,为解决这一问题,本文借鉴图论网络分析理论提出了景观中心度的概念及度量方法,并探讨了景观中心度在生态网络规划与管理中的应用内容和框架.景观中心度方法虽然可为景观规划与管理中关键景观要素的确定和连续生态网络的构建提供新途径,但仍需从指标的生态意义、实验数据的分析和简单通用的分析软件等方面对该方法进行验证和完善.     

Stylet penetration by larvae of the greenhouse whitefly on cucumber

Probing behaviour of Trialeurodes vaporariorum (Westwood) larvae was monitored using the DC electrical penetration graph (EPG) technique on the host plant cucumber. EPGs were recorded for 16 h, simultaneously with honeydew excretion using a honeydew clock. Three waveforms were distinguished: a pathway waveform (C), and two phloem waveforms, one with a high (H), and one with a low frequency (L) signal. The C waveform mainly occurred in the crawler stage of the 1st instar larvae. EPGs recorded from larvae during and after moulting indicated that the process involves stylet withdrawal; hence the stylets of each new instar need to penetrate again from the leaf surface to the phloem.All sessile stages, from L1 to pre-pupa, spent almost their entire time in waveforms H and L. These waveforms alternated more frequently in the early instars than during the later ones, in which the H waveform became predominant. The H waveform was highly correlated with honeydew excretion and thus phloem sap ingestion. The L waveform was not related to honeydew excretion but EPGs indicated that the stylet tips remain in a sieve element during both waveforms. Periods of honeydew production demonstrated a delay of 30–40 min in relation to the onset and end of H and L waveforms. This delay is presumably related to the time needed for food passing through, or emptying of, the insect's gut. From the 1st instar to the pre-pupa, the frequency of excreted honeydew droplets decreased but their size increased, causing a net increase of the excretion rate.     

B型烟粉虱在6个烟草品种上的取食行为

【背景】不同烟草品种会影响B型烟粉虱的取食选择性,但具体的机制尚不明确。刺吸电波图（EPG）技术是研究刺吸式昆虫对寄主植物取食选择性的重要手段,通过烟粉虱取食产生的电信号,可以分析其对不同烟草品种的取食差异。【方法】应用EPG技术对B型烟粉虱雌成虫在6个烟草品种（翠碧1号、K326、闽烟7号、云烟85、云烟87、红花大金元）上的取食行为进行比较研究。【结果】6个烟草品种上有效记录的雌成虫数均为18头,在翠碧1号、K326、闽烟7号、云烟87、云烟85和红花大金元叶片上能够到达韧皮部的个体数分别为15、15、12、13、15和15头,能够持续吸食的个体数分别为13、14、8、12、14和15头。烟粉虱雌成虫在6个烟草品种上的非刺探（np）波所占的比例差异显著,在红花大金元上所占的比例最小,显著低于其他5个品种。雌成虫在红花大金元和K326上E1波的总持续时间显著短于闽烟7号和云烟87。雌成虫在红花大金元上E2波的总持续时间显著长于其他5个品种,而在闽烟7号、云烟87和云烟85上显著短于其他3个品种。【结论与意义】在6个烟草品种中,B型烟粉虱雌成虫最喜食红花大金元,最不喜食闽烟7号和云烟87。因此,在福建省B型烟粉虱的发生区,选择烟草品种时可根据实际情况减少红花大金元的种植,增多闽烟7号和云烟87等抗B型烟粉虱品种的种植。     

Effect of mineral oils on host plant selection and probing behavior of Rhopalosiphum padi

Aphids that colonize and reproduce on potato are some of the most efficient vectors of Potato virus Y (PVY) (Potyviridae: Potyvirus), and hence these aphids have been the focus of the majority of studies to date. However, other non‐colonizing aphids can also function as vectors. Mineral oil is the only product available to growers that effectively prevents the spread of PVY in potato seed production. Most previous studies focused on the effect of mineral oil on the behavior of aphids on their preferential host plant, and consequently there is a lack of information for non‐colonizing aphids on potato plants. The objective of this study was to determine the effect of spraying potatoes with one of two mineral oils, Superior 70 or Vazyl‐Y, on host selection and probing behavior of the non‐colonizing aphid Rhopalosiphum padi (L.) (Hemiptera: Aphididae). The electrical penetration graph (EPG) technique, combined with ethological observations, determined that there was no difference in R. padi behavior on potato plants treated with Superior 70. However, there were few significant changes in R. padi behavior on plants sprayed with Vazyl‐Y, including a delay in the initiation of stylet penetration and an increase in the duration of xylem sap ingestion. These new data support previous results and confirm that the mode of action of mineral oil in the reduction of the spread of PVY is not solely due to the modification of the behavior of aphids.     

Plant water stress intensity mediates aphid host choice and feeding behaviour

1. The effects of drought-induced changes in plant quality on aphid performance and population growth is well-studied. The response of aphid behaviour to plant water limitation has received less attention. Water limitation may affect host-plant colonization by altering the attractiveness of plants. Additionally, plant water limitation may inhibit feeding site establishment and phloem ingestion.
2. Our goal was to examine bird cherry-oat aphid (Rhopalosiphum padi L.) host selection and feeding behaviour under water limitation. We assessed aphid response to well-watered, mildly-stressed, and highly-stressed wheat (Triticum aestivum L.) by evaluating (i) host-plant selection through two-choice assays, (ii) feeding behaviour using the electrical penetration graph technique, and (iii) phloem ingestion by quantifying honeydew production.
3. Aphids were less likely to select highly stressed plants than a mildly stressed or well-watered alternative. Aphids did not distinguish between mildly stressed and well-watered plants. Aphid feeding behaviours, including duration of phloem ingestion, were not affected by water availability. However, honeydew production was reduced under both levels of water limitation. These results suggest that the volume of phloem ingested by aphids per unit time declined on stressed plants. The combination of lower colonization and diminished access to food on stressed plants may lead to a reduction in aphid abundance, independent of the direct effects of nutrition on individual aphid performance.
4. This study highlights the potential contribution of herbivore behaviour to documented changes in aphid abundance on stressed plants and underscores the important role of plant water stress intensity in mediating plant-herbivore interactions.

     

Multi-node selection of patches for protecting habitat connectivity: Fragmentation versus reachability

Landscape connectivity is of major importance in biodiversity conservation, and is one of the key aspects to be taken into consideration in the spatial design of networks of protected areas. Graph-theoretical approaches are useful in modelling habitat connectivity and defining priority areas for the protection of connectivity. This prioritization can be done based on rankings of the centrality (or importance) of individual habitat patches. Moreover, the centrality of a set of n habitat patches can also be calculated. Importantly, the most central single patch is not necessarily a member of the most central group of n patches (non-nested topology). Multi-node analyses identify groups of patches that maximally complement each other in order to increase the protection of connectivity for the whole network. We apply multi-node analyses to the prioritization of habitat patches for five vulnerable bird species in Catalonia, Spain, using two different approaches to connectivity, based on fragmentation and reachability. Groups of patches based on fragmentation are usually concentrated in core areas, while reachability groups are widely spread. Fragmentation sets have higher centrality value for low-mobility species, and reachability sets for long distance dispersers. The protection of the networks against fragmentation requires fewer patches, allows for more gradual implementation and is currently better accounted for by the Natura 2000 network of protected areas, while the protection of reachability is less costly and more efficient in terms of area requirements. Our work contributes to the development of landscape graph analysis for reserve design towards multi-node approaches.     

Merging chemical and biological space: Structural mapping of enzyme binding pocket space

Structure‐based drug design tries to mutually map pharmacological space populated by putative target proteins onto chemical space comprising possible small molecule drug candidates. Both spaces are connected where proteins and ligands recognize each other: in the binding pockets. Therefore, it is highly relevant to study the properties of the space composed by all possible binding cavities. In the present contribution, a global mapping of protein cavity space is presented by extracting consensus cavities from individual members of protein families and clustering them in terms of their shape and exposed physicochemical properties. Discovered similarities indicate common binding epitopes in binding pockets independent of any possibly given similarity in sequence and fold space. Unexpected links between remote targets indicate possible cross‐reactivity of ligands and suggest putative side effects. The global clustering of cavity space is compared to a similar clustering of sequence and fold space and compared to chemical ligand space spanned by the chemical properties of small molecules found in binding pockets of crystalline complexes. The overall similarity architecture of sequence, fold, and cavity space differs significantly. Similarities in cavity space can be mapped best to similarities in ligand binding space indicating possible cross‐reactivities. Most cross‐reactivities affect co‐factor and other endogenous ligand binding sites. Proteins 2009. © 2008 Wiley‐Liss, Inc.     

The frequency and position of stable associations offset their transitivity in a diversity of vertebrate social networks

When the estimated strength of social associations corresponds to the proportion of time spent together, strong links, those that take up most of the recorded time of individuals, are compulsorily transitive and tend to occur in clusters. However, I describe three ways in which the frequency and position of strong associations apparently offset the expected transitivity of strong links in published association networks from 26 species of vertebrates. Instead of occurring in groups of three, strong links were mostly isolated. When they did occur in clusters, the clusters were small. The phenomena increased in intensity as the overall number of links of all strengths and the overall network transitivity increased. Since stable transitive motifs are beneficial to cooperation, these results can help explain why cooperative behaviors are not more frequent than they are in group-living vertebrates. Inversely, stable transitive motifs may be rare and small because the benefits of cooperation do not overcome the costs associated with these motifs. The summary statistics developed for this study captured information not conveyed by other network-level metrics; thus they may help quantify the socio-spatial structure of populations and potentially tease apart the environmental, species-specific, and individual drivers.