棉蚜寄主专化型及其形成的行为机理

通过生活在甜瓜和棉花上的棉蚜Aphisgossypii Glover的行为,研究棉蚜的寄主专化型及其形成的行为机理。生物学观察显示： 两类棉蚜在寄主植物相互交换以后,定居数显著减少,棉花蚜型棉蚜的繁殖系数及若虫存活率显著下降,说明棉蚜存在甜瓜蚜型和棉花蚜型两种寄主专化型。通过刺探电位技术研究棉蚜的取食行为,以探索其寄主专化型形成的行为机理。结果表明： 甜瓜蚜型棉蚜在棉花上的取食行为容易被中断,但其口针定位韧皮部的能力并没有显著削弱;而棉花蚜型棉蚜在甜瓜上的取食行为受到更大的影响,口针无法顺利定位至韧皮部,并在2 h内根本无法在筛管内取食。生物学观察和EPG取食行为分析都显示： 与甜瓜蚜型棉蚜相比,棉花蚜型棉蚜对寄主的要求更严格-寄主专化程度更高,对寄主的利用率更高。     

模糊图论分类的截取水平选择

在数量分类中,模糊图论的最大树方法可直接依据模糊相似系数得到树状图。但至目前为止,模糊图论分类中的截取水平通常由分析者主观给定,或者是以逐步试验、逐步修改的方法确定的。用太白山针叶林的数量分类研究结果表明,模糊图论分类的截取水平应选在模糊关系变化较大处,并可用数学方法确定。研究的植被分类实例结果与模糊聚类分析是一致的。     

Comparison of Acyrthosiphon pisum probing behaviors on different alfalfa cultivars

Acyrthosiphon pisum (Harris) is a major pest of alfalfa worldwide. Here, we evaluated the resistance of eight alfalfa cultivars to A. pisum to identify resistant cultivars. The Giga-8 DC-EPG technique was used to record differences in electrical waveform patterns of probing behavior to identify cultivars with higher resistance. The frequency and average duration of EPG waveforms significantly differed among the cultivars, with eight documented waveforms (np, C, pd, E1, E2, sE2, F, and G). The longer duration of np, C, F and E1 waveforms reflected stronger resistance, whereas longer sE2 waveforms reflected weaker resistance. The resistance-related waveforms, np and C, occurred most frequently with Sardi 7, the time of the first E waveforms were the latest, duration of G waveforms and F waveforms were the longest, the feeding waveforms E2 and sE2 were the shortest, the time of reaching phloem for feeding was the latest, with notable resistance in leaf epidermis, mesophyll and phloem. The number of C waveforms occurring with Gibraltar were the least, duration of np waveforms was short, feeding waveforms were long, time to reach the phloem for feeding was early, and the resistance was not pronounced in various tissues. After comprehensive evaluation, the resistance levels of 8 alfalfa cultivars were as follows: High resistance, Sardi 7; Resistance, Zhongcao No. 3, Derby, WL319HQ; Low resistance, Golden Empress, Algonquin, Zhaodong; Susceptible, Gibraltar. In conclusion, evaluation of cultivar resistance to aphids can provide baseline data for selecting and planting cultivars with high local resistance.     

Recent mathematical approaches to reconstruct phylogenies: A chemosystematist's and botanist's view

Some basic problems of mathematical phylogenetics are discussed. While algorithms regularly depend on the principle of parsimony, some features of phylogenesis interfere with that principle. Nonrandomness of the distribution of mutations as well as the inconstancy of the molecular clock in time and within a given sequence can bias the calculated relationships of closely related taxa. True comparability of sequences is difficult to establish, since this requires defining of homology of positions and of functions of amino acids as well. Parallelism and convergence can give rise to errors in establishing homology. Furthermore, they are difficult to be integrated into a consistent mathematical approach. The asymmetry of identity versus difference matrices is discussed. Common mathematical procedures implicate the monophyletic hypothesis as well as strict dichotomy of the final tree. Real phylogeny demands to introduce more flexible approaches with respect to monophyly and dichotomy. Graph theory offers the possibility to prove the minimality of a given tree and to develop more flexible approaches. The consequences of altering the procedures to compare sequences can be tested. This is demonstrated by calculations with a set of 15 cytochromes from various taxa. To interpret a calculated tree requires a sharp distinction between taxonomy and phyletics. This is exemplified for the case of directly linked taxa. The limits of resolving uncertain relationships by accumulating more data are mentioned.This paper was partly presented at the Symposium Theory and practice of botanical classification, during the 14th International Botanical Congress, Berlin, July 1987.     

Using gap‐crossing capacity to evaluate functional connectivity of two Atlantic rainforest birds and their response to fragmentation

Abstract One of the main consequences of habitat loss and fragmentation is the increase in patch isolation and the consequent decrease in landscape connectivity. In this context, species persistence depends on their responses to this new landscape configuration, particularly on their capacity to move through the interhabitat matrix. Here, we aimed first to determine gap‐crossing probabilities related to different gap widths for two forest birds (Thamnophilus caerulescens, Thamnophilidae; and Basileuterus culicivorus, Parulidae) from the Brazilian Atlantic rainforest. These values were defined with a playback technique and then used in analyses based on graph theory to determine functional connections among forest patches. Both species were capable of crossing forest gaps between patches, and these movements were related to gap width. The probability of crossing 40 m gaps was 50% for both species. This probability falls to 10% when the gaps are 60 m (for B. culicivorus) or 80 m (for T. caerulescens). Actually, birds responded to stimulation about two times more distant inside forest trials (control) than in gap‐crossing trials. Models that included gap‐crossing capacity improved the explanatory power of species abundance variation in comparison to strictly structural models based merely on patch area and distance measurements. These results highlighted that even very simple functional connectivity measurements related to gap‐crossing capacity can improve the understanding of the effect of habitat fragmentation on bird occurrence and abundance.     

UV-B胁迫小麦上麦长管蚜的生命表参数和取食行为

【目的】为明确UV-B胁迫小麦对麦长管蚜Sitobion avenae (Fabricius)种群生命表参数和取食行为的影响。【方法】采用特定年龄生命表方法和刺探电位图谱（EPG）技术, 研究了不同强度UV-B胁迫处理小麦对麦长管蚜生命表参数和取食行为的影响。【结果】生命表结果表明, 取食高强度（0.75 mW/cm²） UV-B辐射小麦后, 麦长管蚜种群内禀增长率r_m、 净增殖率R₀、 繁殖力F下降, 平均世代周期T缩短, 且差异显著(P<0.05); 取食低强度（0.2 mW/cm²）UV-B辐射小麦后, 麦长管蚜种群生命表参数与对照组（正常光照处理小麦饲喂的蚜虫种群）无显著差异(P>0.05)。刺探电位图谱结果显示, 高强度UV-B处理组np波(即非取食)数量显著增加, pd波（刺探波）首次出现的时间延迟, 表明紫外处理小麦干扰了蚜虫的在叶表面的正常刺探活动, 延长了搜索和刺探时间; C波持续时间显著延长, 反映取食难度加大, 有效取食时间缩短, 从而影响种群生命表参数; 而低强度UV-B处理组小麦对蚜虫取食行为影响与对照组差异不显著, 但pd波首次出现时间显著延长。【结论】高强度UV-B胁迫小麦会严重影响麦长管蚜的生长发育、 繁殖与取食行为。     

Distortion of effects caused by indirect confounding

Undetected confounding may severely distort the effect of anexplanatory variable on a response variable, as defined by astepwise data-generating process. The best known type of distortion,which we call direct confounding, arises from an unobservedexplanatory variable common to a response and its main explanatoryvariable of interest. It is relevant mainly for observationalstudies, since it is avoided by successful randomization. Bycontrast, indirect confounding, which we identify in this paper,is an issue also for intervention studies. For general stepwise-generatingprocesses, we provide matrix and graphical criteria to decidewhich types of distortion may be present, when they are absentand how they are avoided. We then turn to linear systems withoutother types of distortion, but with indirect confounding. Forsuch systems, the magnitude of distortion in a least-squaresregression coefficient is derived and shown to be estimable,so that it becomes possible to recover the effect of the generatingprocess from the distorted coefficient.     

Irreversible thelytokous reproduction in Muscidifurax uniraptor

Three encyrtid parasitoids Apoanagyrus (Epidinocarsis) diversicornis, Aenasius vexans, and Acerophagus coccois (Hymenoptera: Encyrtidae) are used to control the cassava mealybug Phenacoccus herreni Cox & Williams (Sternorrhyncha: Pseudococcidae), an important pest of cassava in South America. The influence of parasitism on the feeding behaviour of mealybugs was studied by observing honeydew secretion and by the electrical penetration graph technique (EPG, DC-system). Honeydew secretions were observed after parasitism until mummy transformation. No strong EPG parameter differences were found between parasitised and control insects. All results indicated that parasitised mealybugs keep feeding on the phloem sap after parasitism until mummy transformation. The main influence of parasitism on EPG parameters is the appearance of a new pattern resembling the E2 pattern at the extracellular level and labelled H. This pattern was also produced with control insects located on an unfavourable feeding site and could be associated with a stress response. It might be related to the still unclear E(c) pattern of aphids. The relationship of H to stylet activities is discussed.     

Does dispersal capacity matter for freshwater biodiversity under climate change?

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