B型烟粉虱对寄主转换的适应性

将B型烟粉虱分别从嗜性较强的番茄上转移到嗜性相对较弱的国抗22棉花、泗棉3号棉花和辣椒上, 以及从嗜性较弱的辣椒上转移到嗜性相对较强的番茄、国抗22棉花和泗棉3号棉花上, 观察寄主转移后的F₁代、F₂代、F₃代烟粉虱产卵效应和寄主适应度的变化;将F₄代烟粉虱再转移到原寄主, 观察烟粉虱产卵效应和寄主适应度的恢复情况。结果表明, 烟粉虱在不同嗜性寄主上的产卵效应存在明显的差异。在不同嗜性的寄主之间转移, 烟粉虱的寄主适应度变化趋势不同, 从嗜性较强的寄主转移到嗜好性相对较弱的寄主上, 烟粉虱的寄主适应度迅速下降;从嗜性较弱的寄主向嗜性较强的寄主转移后, 烟粉虱的适应度则会迅速提高。烟粉虱对新寄主的适应速度与其对原寄主和新寄主之间的嗜性差异程度有关, 但一般经过1-2个世代后, 产卵效应会逐渐恢复到烟粉虱在该寄主上的正常水平。从过渡寄主转移到原寄主, 烟粉虱的寄主适应度变化符合一般的寄主转移规律, 但嗜性相对较强的过渡寄主可以刺激烟粉虱提高寄主适应性。     

Histopathology of Okra and Ridgeseed Spurge Infected with Meloidodera charis

Histological observations of okra Abelomoschus esculentus ''Clemson Spineless'' and ridgeseed spurge Euphorbia glyptosperma (a common weed) infected with Meloidodera charis Hopper, indicated that the juvenile nematode penetrated the roots intercellularly. Within 5 days after plant emergence the nematode positioned its body in the cortical tissue parallel to the vascular system. By 10 days after plant emergence the juvenile had extended its head into the vascular system and initiated giant cell formation, generally in protophloem tissue. Giant cells were one celled and usually multi-nucleate. Eggs were observed in the female body 30 days after plants emerged and juveniles were found within the female body by 40 days. Nematode development progressed equally in the root system of either host plant. Generally, throughout the nematode''s life cycle its entire body remained inside the cortical tissue of okra. In ridgeseed spurge, however, the posterior portion of the female erupted through the host epidermis as early as 15 days after plant emergence; only the head and neck remained embedded in the host. The nematode caused extensive tissue disruption in the cortical and vascular system of both plant species. Corn, Zea mays, was another host of the nematode.     

Impact of the experimental removal of lizards on Lyme disease risk

The distribution of vector meals in the host community is an important element of understanding and predicting vector-borne disease risk. Lizards (such as the western fence lizard; Sceloporus occidentalis) play a unique role in Lyme disease ecology in the far-western United States. Lizards rather than mammals serve as the blood meal hosts for a large fraction of larval and nymphal western black-legged ticks (Ixodes pacificus--the vector for Lyme disease in that region) but are not competent reservoirs for the pathogen, Borrelia burgdorferi. Prior studies have suggested that the net effect of lizards is to reduce risk of human exposure to Lyme disease, a hypothesis that we tested experimentally. Following experimental removal of lizards, we documented incomplete host switching by larval ticks (5.19%) from lizards to other hosts. Larval tick burdens increased on woodrats, a competent reservoir, but not on deer mice, a less competent pathogen reservoir. However, most larvae failed to find an alternate host. This resulted in significantly lower densities of nymphal ticks the following year. Unexpectedly, the removal of reservoir-incompetent lizards did not cause an increase in nymphal tick infection prevalence. The net result of lizard removal was a decrease in the density of infected nymphal ticks, and therefore a decreased risk to humans of Lyme disease. Our results indicate that an incompetent reservoir for a pathogen may, in fact, increase disease risk through the maintenance of higher vector density and therefore, higher density of infected vectors.     

Additional Hosts for the Ring Nematode,Criconemella xenoplax

Some common legumes and weeds indigenous to peach orchards in South Carolina were tested in greenhouse experiments to determine their host suitability for Criconemella xenoplax. Legumes that were hosts for the nematode were dwarf English trefoil (Lotus corniculatus var. arvensis), big trefoil (L. uliginosis), birdsfoot trefoil (L. corniculatus), narrowleaf birdsfoot trefoil (L. tenuis), ball clover (Trifolium nigrescens), rose clover (T. hirtum), subterranean clover (T. subterraneum), striate lespedeza (Lespedeza striata), and partridge pea (Cassiafasciculata). Most nonleguminous plants tested did not support population increases, but small increases were observed on orchardgrass (Dactylis glomerata), broadleaf signalgrass (Brachiaria platyphylla), purslane (Portulaca oleracea), and Carolina geranium (Geranium carolinianum). Results indicate that leguminous plants probably should not be used as ground cover or rotation crops for plants that are injured by C. xenopax.     

Histopathology and Host Range Studies of the Redwood Nematode Rhizonema sequoiae

Second-stage larvae of Rehizonma sequoiae Cid del Prado Vera et al. tunnel through the cortex of the redwood Sequoia sempervirens (D. Don) Endl. root to the vascular tissue where each developing female induces a single ovoid or occasionally spherical giant cell with a single ovoid to spherical nucleus containing one to four enlarged nucleoli. Nematode tunnels are filled with a gel material and often contain second-stage larvae and males. There is tissue necrosis around females, and cortical tissue is destroyed after infection by many second-stage larvae. R. sequoiae females developed to maturity on S. sempervirens, Acer macrophyllum Pursh, AInus rhombifolia Nutt., Libocedrus decurrens Torr, Pseudotsuga menziesii (Mirb.) Franco, and Sequoiadendron giganteum (Lindl.) Decne. In the Marin County, California, forest mature females were also found naturally infecting Lithocarpus densiflorus (Hook &Arn.) Rehd., Umbellularia californica (Hook &Arn.) Nutt., and Arbutus menziesii Pursh.     

Host manipulation by parasites in the world of dead-end predators: adaptation to enhance transmission?

Trophically transmitted parasites often alter their intermediate host's phenotype, thereby predisposing the hosts to increased predation. This is generally considered a parasite strategy evolved to enhance transmission to the next hosts. However, the adaptive value of host manipulation is not clear as it may be associated with costs, such as increased susceptibility to predators that are unsuitable next hosts for the parasites. We examined the ratio between the benefits and costs of host manipulation for transmission success of Acanthocephalus lucii (Acanthocephala), a parasite that alters the hiding behaviour and pigmentation of its isopod hosts. We experimentally compared the susceptibility of infected and uninfected isopods to predation by perch (Perca fluvialis; definitive host of the parasite) and dragonfly larvae (dead end). We found that the parasite predisposed the isopods to predation by both predators. However, the increased predation vulnerability of the infected isopods was higher towards perch. This suggests that, despite the costs due to non-host predation, host manipulation may still be advantageous for the parasite.     

Enzooticity of the dogs,the reservoir host of Thelazia callipaeda,in Korea

The reservoir hosts of Thelazia callipaeda were examined. The eyes of the 76 dogs raised at farm. 78 military dogs (shepherds), 96 cattle, and 105 pigs were investigated for the presence of eyeworm. Among them, six worms of T. callipaeda were collected from two dogs raised at farm (2.7%), and 188 worms from 26 shepherds (33.5%). No worms were recovered from the cattle or pigs. These results suggest that the dogs, especially the military dogs are serving as a reservoir host of T. callipaeda in Korea.     

西花蓟马对蔬菜寄主的选择性研究

通过西花蓟马在田间不同蔬菜上的种群数量、在室内对不同蔬菜的自由选择和不同蔬菜对西花蓟马生长发育和繁殖的影响等方面,研究了西花蓟马对蔬菜寄主的选择性。结果表明西花蓟马在田间可危害24种蔬菜,但在不同蔬菜上种群数量差异很大,存在明显的寄主选择性,对黄瓜、四季豆、茄子、萝卜和香菜的嗜食度很高,为最适宜寄主,而对番茄、蒜、芹菜等11种蔬菜的嗜食度较低,为非适宜寄主。西花蓟马在室内的自由选择结果表明西花蓟马在7种不同蔬菜上着落的成虫数量和产卵量不同,其选择性为黄瓜＞四季豆＞茄子＞莴苣＞甘蓝＞芹菜＞蒜。不同蔬菜对西花蓟马的发育历期和产卵量有明显的影响,西花蓟马在黄瓜上发育最快,在四季豆上产卵量最高。西花蓟马对蔬菜寄主的选择性在田间的调查结果和室内实验结果基本一致。     

Drosophila as a model system to unravel the layers of innate immunity to infection

Innate immunity relies entirely upon germ-line encoded receptors, signalling components and effector molecules for the recognition and elimination of invading pathogens. The fruit fly Drosophila melanogaster with its powerful collection of genetic and genomic tools has been the model of choice to develop ideas about innate immunity and host-pathogen interactions. Here, we review current research in the field, encompassing all layers of defence from the role of the microbiota to systemic immune activation, and attempt to speculate on future directions and open questions.     

Divergent host-plant use promotes reproductive isolation among cynipid gall wasp populations

Ecological speciation occurs when reproductive isolation evolves as a consequence of divergent natural selection among environments. A direct prediction of this process is that ecologically divergent pairs of populations will exhibit greater reproductive isolation than ecologically similar pairs of populations. By comparing allopatric populations of the cynipid gall wasp Belonocnema treatae infesting Quercus virginiana and Quercus geminata, we tested the role that divergent host use plays in generating ecological divergence and sexual isolation. We found differences in body size and gall structure associated with divergent host use, but no difference in neutral genetic divergence between populations on the same or different host plant. We observed significant assortative mating between populations from alternative host plants but not between allopatric populations on the same host plant. Thus, we provide evidence that divergent host use promotes speciation among gall wasp populations.     

A test of the sympatric host race formation hypothesis in Neodiprion (Hymenoptera: Diprionidae)

Theory suggests that sympatric speciation is possible; however, its prevalence in nature remains unknown. Because Neodiprion sawflies are host specialists and mate on their hosts, sympatric speciation via host shifts may be common in this genus. Here, we test this hypothesis using near-complete taxonomic sampling of a species group, comprehensive geographical and ecological data, and multiple comparative methods. Host-use data suggest that host shifts contributed to the evolution of reproductive isolation in Neodiprion and previous work has shown that gene flow accompanied divergence. However, geographical data provide surprisingly little support for the hypothesis that host shifts occurred in sympatry. While these data do not rule out sympatric host race formation in Neodiprion, they suggest that this speciation mode is uncommon in the genus and possibly in nature.     

Relative Virulence of Meloidogyne incognita Host Races on Soybean

Sensitivity and host efficiency of susceptible (''Lee 68'', ''Coker 156'') and resistant (''Bragg'', ''Centennial'', ''Forrest'', ''Lee 74'') soybean (Glycine max (L.) Merr.) cultivars for races of Meloidogyne incognita (Mi) were determined in greenhouse experiments. Eight Mi populations collected from the southeastern United States were utilized. All Mi races reproduced readily on Lee 68 and Lee 74 and moderately on Forrest and Bragg. Coker 156 exhibited resistance to races 1 and 2, and some race 3 populations, but was very susceptible to certain race 3 and 4 populations. Reproduction of all races was lowest on Centennial. Forrest and Centennial shoot growth was not significantly suppressed by any race. There were no distinct differences in virulence between races except for a race 3 population which reproduced readily on all cultivars, stunting their growth. Considerable variation in reproduction existed within races 1 and 3.     

Does early learning drive ecological divergence during speciation processes in parasitoid wasps?

Central to the concept of ecological speciation is the evolution of ecotypes, i.e. groups of individuals occupying different ecological niches. However, the mechanisms behind the first step of separation, the switch of individuals into new niches, are unclear. One long-standing hypothesis, which was proposed for insects but never tested, is that early learning causes new ecological preferences, leading to a switch into a new niche within one generation. Here, we show that a host switch occurred within a parasitoid wasp, which is associated with the ability for early learning and the splitting into separate lineages during speciation. Lariophagus distinguendus consists of two genetically distinct lineages, most likely representing different species. One attacks drugstore beetle larvae (Stegobium paniceum (L.)), which were probably the ancestral host of both lineages. The drugstore beetle lineage has an innate host preference that cannot be altered by experience. In contrast, the second lineage is found on Sitophilus weevils as hosts and changes its preference by early learning. We conclude that a host switch has occurred in the ancestor of the second lineage, which must have been enabled by early learning. Because early learning is widespread in insects, it might have facilitated ecological divergence and associated speciation in this hyperdiverse group.     

Infection of Cultured Thin Cell Layer Roots of Lycopersicon esculentum by Meloidogyne incognita

A new aseptic culture system for studying interactions between tomato (Lycopersicon esculentum) and Meloidogyne incognita is described. Epidermal thin cell layer explants from peduncles of tomato produced up to 20 adventitious roots per culture in 4-9 days on Murashige &Scoog medium plus kinetin and indole acetic acid. Rooted cultures were transferred to Gamborg''s B-5 medium and inoculated with infective second-stage juveniles. Gall formation was apparent 5 days after inoculation and egg production by mature females occurred within 25 days at 25 C in the susceptible genotypes Rutgers and Red Alert. Resistant genotypes LA655, LA656, and LA1022 exhibited a characteristic hypersensitive response. This system provides large numbers of cultured root tips for studies on the molecular basis of the host-parasite relationship.     

Adjunctive steroid in HIV-negative patients with severe Pneumocystis pneumonia

Background

High-dose steroid therapy has been proven effective in AIDS-related Pneumocystis pneumonia (PCP) but not in non-AIDS-related cases. We evaluated the effects on survival of steroids in HIV-negative patients with PCP.

Methods

Retrospective study patients admitted to the ICU with hypoxemic PCP. We compared patients receiving HDS (≥1 mg/Kg/day prednisone equivalent), low-dose steroids (LDS group, <1 mg/Kg/day prednisone equivalent), and no steroids (NS group). Variables independently associated with ICU mortality were identified.

Results

139 HIV-negative patients with PCP were included. Median age was 48 [40–60] years. The main underlying conditions were hematological malignancies (n=55, 39.6%), cancer (n=11, 7.9%), and solid organ transplantation (n=73, 52.2%). ICU mortality was 26% (36 deaths). The HDS group had 72 (51.8%) patients, the LDS group 35 (25%) patients, and the NS group 32 (23%) patients. Independent predictors of ICU mortality were SAPS II at ICU admission (odds ratio [OR], 1.04/point; [95%CI], 1.01-1.08, P=0.01), non-hematological disease (OR, 4.06; [95%CI], 1.19-13.09, P=0.03), vasopressor use (OR, 20.31; 95%CI, 6.45-63.9, P<0.001), and HDS (OR, 9.33; 95%CI, 1.97-44.3, P=0.02). HDS was not associated with the rate of ICU-acquired infections.

Conclusions

HDS were associated with increased mortality in HIV-negative patients with PCP via a mechanism independent from an increased risk of infection.     

Morphology, biology and taxonomy of Dendritobilharzia loossi Skrjabin, 1924 (Trematoda: Bilharziellidae), a parasite of Pelecanus onocrotalus (Pelecanidae) and Anas plathyrinchos (Anatidae)

Life cycles of Dendritobilharzia loossi Skrjabin, 1924, a parasite of waterbirds, and its morphobiological traits are studied and described. Mollusks Anisus spirorbis, the infection rate of which in natural environments reaches 1.3-1.9%, were recorded as intermediate hosts under conditions of Uzbekistan. The development of this trematode in intermediate and definitive hosts lasts for 26 and 15 days, respectively. Diagnostic traits of the trematodes during all stages of their ontogeny are reviewed.     

Resistance of Cotton to the Root-Knot Nematode, Meloidogyne incognita

Cotton plants resistant to Meloidogyne incognita had roots characterized by fewer and smaller galls, and females that produced fewer egg masses containing fewer eggs than did susceptible plants. Many galls on resistant roots contained no nematodes at the time of examination. Penetration of the resistant cultivar was equal to that of the susceptible cultivar and independent of the number of nematodes in the inoculum. Fewer nematodes penetrated resistant or susceptible plants with eight leaves than those with fewer leaves. Reciprocal grafts of resistant and susceptible plants failed to confer resistance or susceptibility to the rootstock.