Egg-laying preference of female fungus gnat Bradysia sp. nr. coprophila (Diptera: Sciaridae) on three different soilless substrates

Fungus gnats, Bradysia spp., are major insect pests in greenhouses. Adult female fungus gnats prefer to lay eggs in growing medium that is microbially active or that contains high amounts of peat moss or hardwood bark. However, egg-laying preference has not been demonstrated quantitatively. This study was designed to determine whether fungus gnat Bradysia sp. nr. coprophila females prefer any of the three soilless growing media provided. The three soilless growing media tested were Metro-Mix 560 with Scott's Coir, Sunshine LC1 Mix, and Universal SB 300 Mix. Initially, the egg-laying potential of the fungus gnat species used in this study was assessed by dissecting mated females after 24, 48, and 72 h. For the egg-laying preference experiment, adults that emerged from pupae were aspirated into a plastic vial, sexed, and then allowed to mate for 24 h. Individual mated females were released into an experimental chamber (15 by 15 by 5-cm plastic container) consisting of four 6-cm petri dishes, three of which contained soilless growing media and one with filter paper (control). In total, there were 50 experimental chambers, with each chamber representing a replication. Females remained in the experimental chambers for 48 h after which the growing media were processed using a flotation/extraction method. The number of eggs laid by female fungus gnats ranged from 21 to 217 with most eggs recovered after 48 h (141.0 +/- 9.3). There were no significant differences among the three soilless growing media in terms of number of eggs laid, although all three growing media were significantly different from the filter paper with higher numbers of eggs laid in the soilless growing media than the filter paper. Despite no significant difference among the growing media in the number of eggs laid, fungus gnat females tended to lay eggs more often, based on the number of petri dishes in which at least one egg was laid, in Metro-Mix 560 (86%) than Sunshine LC1 (66%), Universal SB 300 (52%), or filter paper (18%). Based on the results of this study, female fungus gnats may not prefer a specific growing medium for oviposition. However, fungus gnat females may rely on other factors not tested in this study such as moisture content and volatiles emitted from growing media in their decision where to lay eggs.     

Formation of homogeneous unilamellar liposomes from an interdigitated matrix

Phospholipid-ethanol-aqueous mixtures containing bilayer-forming lipids and 20-50 wt.% of water form viscous gels. Further hydration of these gels results in the formation of liposomes whose morphology depends upon the lipid type. Upon hydration of gels containing mixtures of the lipids 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and 1-palmitoyl-2-oleoyl-phosphatidylglycerol (POPG), small homogeneous and unilamellar liposomes were produced. In contrast, hydration of gels containing only POPC resulted in formation of large multilamellar liposomes. Likewise, mulitlamellar liposomes resulted when this method was applied to form highly fusogenic liposomes comprised of the novel negatively charged N-acyl-phosphatidylethanolamine (NAPE) mixed with di-oleoyl-phosphatidylcholine (DOPC) (7:3) [T. Shangguan, C.C. Pak, S. Ali, A.S. Janoff, P. Meers, Cation-dependent fusogenicity of an N-acyl phosphatidylethanolamine, Biochim. Biophys. Acta 1368 (1998) 171-183]. In all cases, the measured aqueous entrapment efficiencies were relatively high. To better understand how the molecular organization of these various gels affects liposome morphology, we examined samples by freeze-fracture transmission electron microscopy and X-ray diffraction. We found that phospholipid-ethanol-water gels are comprised of highly organized stacks of lamellae. A distinct feature of the gel samples that result in small unilamellar liposomes is the combination of acyl chain interdigitation and net electrostatic charge. We speculate that the mechanism of unilamellar liposome formation proceeds via formation of stalk contacts between neighboring layers similar to membrane hemifusion intermediates, and the high aqueous entrapment efficiencies make this liposome formation process attractive for use in drug delivery applications.     

我国奶牛乳房炎致病性金黄色葡萄球菌血清型分布

本试验采用玻片凝集法对从临床型乳房炎病乳中分离获得的56株金黄色葡萄球菌进行血清型分型。结果表明336型占67.9%(38/56),5型占7.1%(4/56),8型占3.6%(2/56)。     

Evolution of the population structure of Venturia inaequalis,the apple scab fungus,associated with the domestication of its host

Evaluating the impact of plant domestication on the population structure of the associated pathogens provides an opportunity to increase our understanding of how and why diseases emerge. Here, we investigated the evolution of the population structure of the apple scab fungus Venturia inaequalis in response to the domestication of its host. Inferences were drawn from multilocus microsatellite data obtained from samples collected on (i) the Central Asian Malus sieversii, the main progenitor of apple, (ii) the European crabapple, Malus sylvestris, a secondary progenitor of apple, and (iii) the cultivated apple, Malus×domestica, in orchards from Europe and Central Asia. Using clustering methods, we identified three distinct populations: (i) a large European population on domesticated and wild apples, (ii) a large Central Asian population on domesticated and wild apples in urban and agricultural areas, and (iii) a more geographically restricted population in M. sieversii forests growing in the eastern mountains of Kazakhstan. Unique allele richness and divergence time estimates supported a host‐tracking co‐evolutionary scenario in which this latter population represents a relict of the ancestral populations from which current populations found in human‐managed habitats were derived. Our analyses indicated that the domestication of apple induced a significant change in the genetic differentiation of populations of V. inaequalis in its centre of origin, but had little impact on its population dynamics and mating system. We discuss how the structure of the apple‐based agrosystem may have restricted changes in the population structure of the fungus in response to the domestication of its host.     

不同细菌对家蝇幼虫抗菌蛋白/肽的诱导效应

利用抑菌圈测量法和毛细管电泳研究、比较不同细菌对家蝇Musca domesticaL.幼虫抗菌蛋白/肽的诱导效应。结果表明,家蝇幼虫受细菌诱导后抗菌活性比对照都有不同程度的增加,同时不同细菌诱导表达样品对于相应的诱导菌均表现很高的抗菌活性。毛细管电泳图谱表明鼠伤寒沙门氏菌Salmonella typhimurium50013诱导后抗菌蛋白/肽表达强度增加了50倍,其它细菌诱导后抗菌蛋白/肽表达强度增加了1～40倍。与G+细菌相比,G-细菌具有更强的诱导效应。结论:家蝇幼虫对不同的细菌刺激有特异性反应,即不同细菌诱导抗菌蛋白/肽的强度、种类和数量都不一致。     

The mechanism of background extinction

Following publication of On the Origin of Species, biologists concentrated on and resolved the mechanisms of adaptation and speciation, but largely ignored extinction. Thus, extinction remained essentially a discipline of palaeontology. Adequate language is not available to describe extinction phenomena because they must be discussed in the passive voice, wherein populations simply ‘go extinct’ without reference to process, specifics, effects, or causality. Extinction is also described typically in terms of its dynamics (including rate or risk), and although correlative variables enhance our ability to predict extinction, they do not necessarily enable an understanding of process. Yet background extinction, like evolution, is a process requiring a functional explanation, without which it is impossible to formulate mechanisms. We define the mechanism of background extinction as a typically long‐term, multi‐generational loss of reproductive fitness. This simple concept has received little credence because of a perception that excess generation of progeny ensures population sustainability, and perhaps the misconception that the loss of reproductive fitness somehow constitutes selection against reproduction itself. During environmental shifts, reproductive fitness is compromised when biotic or abiotic extremes consistently exceed existing norms of reaction. Subsequent selection will now favour individual survival over reproductive fitness, initiating long‐term negative selection pressure and population decline. Background extinction consists typically of two intergrading phases: habitat attenuation and habitat dissolution. These processes generate the relict populations that characterize many species undergoing background extinction. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 105 , 255–268.