Free fatty acids from the weed,Polygonum orientale leaves for attraction of the potential biocontrol agent,Galerucella placida (Coleoptera: Chrysomelidae)

Extraction, thin layer chromatography and gas chromatography-mass spectrometry of leaf surface waxes of Polygonum orientale L. (Polygonaceae) weed revealed 11, 15 and 11 free fatty acids in young, mature and senescent stages. Oleic acid was the predominant in young leaves (5950 ± 111 µg); whereas palmitic acid was the predominant fatty acids, representing 4247.5 ± 23 and 6644 ± 110 µg in mature and senescent leaves, respectively. Both tridecanoic and heneicosanoic acids were not detected in young and senescent leaves, and myristic and heptadecanoic acids were not identified in young leaves; whereas lauric and nonadecanoic acids were not detected in senescent leaves. The free fatty acids from young, mature and senescent weed leaves, and the mixtures of synthetic fatty acids mimicking free fatty acids of three types of weed leaves attracted female Galerucella placida (Coleoptera: Chrysomelidae) at the minimal amounts of 2, 1 and 2 leaf equivalent free fatty acids, respectively, in Y-shaped glass tube olfactometer bioassays under laboratory conditions. Individual synthetic pentadecanoic, palmitoleic, stearic, nonadecanoic and docosanoic acids at 44.82, 9.91, 92.22, 18.33 and 15.88 µg, respectively, elicited attraction of the insect. A synthetic blend of 3.59, 7.89, 44.82, 9.91, 32.31, 18.33 and 15.88 µg of lauric, myristic, pentadecanoic, palmitoleic, heptadecanoic, nonadecanoic and docosanoic acids, respectively, indicated highest attraction of the insect.     

Effects of pyriproxyfen and buprofezin on immature development and reproduction in the stable fly*

The stable fly, Stomoxys calcitrans (L.) (Diptera: Muscidae), is one of the most significant biting flies that affect cattle. The use of traditional insecticides for stable fly control has only a limited success owing to the insect's unique feeding behaviours and immature development sites. A laboratory study was conducted to evaluate the effects of two insect growth regulator (IGR) products, pyriproxyfen and buprofezin, on the development of the immature stages of the stable fly and the effects of pyriproxyfen on oviposition and egg hatch. Both pyriproxyfen and buprofezin had significant inhibitory effects on immature development. The LC₅₀s of pyriproxyfen and buprofezin were 0.002 and 18.92 p.p.m., respectively. Topical treatment of adult females with different doses of pyriproxyfen had significant negative effects on both female oviposition and egg hatching when 1‐ and 3‐day‐old females were treated, and the effects were dose dependent. A significant reduction in the mean number of eggs laid was observed only at the highest pyriproxyfen dose (8 µg/fly) and egg hatch was unaffected by pyriproxyfen treatment when 5‐day‐old females were treated. Results from the present study indicate that pyriproxyfen has the potential to be used as part of an integrated stable fly management programme.     

The role of volatiles from cruciferous plants and pre-flight experience in the foraging behaviour of the specialist parasitoid Cotesia plutellae

The braconid Cotesia plutellae is an important larval parasitoid of the diamondback moth (Plutella xylostella), a major pest of crucifers in the tropics and sub-tropics. The in-flight searching behaviour of C. plutellae was investigated in a wind tunnel and the close-range attack behaviour observed in cages. The relative importance of volatile stimuli emanating from the plant-host-complex, oilseed rape (Brassica napus) – P. xylostella, in the long-range attraction of C. plutellae was investigated. Plants that were mechanically damaged, or damaged by P. xylostella larvae, were attractive to the parasitoid. Host-damaged leaves remained attractive to the parasitoid after removal of the host larvae. These results indicate that C. plutellae predominantly uses plant derived stimuli in its in-flight searching behaviour. An oviposition experience or contact with a host-damaged leaf prior to the bioassay significantly increased the response to these volatile cues. The foraging behaviour of C. plutellae is compared with other braconid larval parasitoids attacking lepidopteran hosts on crucifers.     

Phytostimulatory effect of Azospirillum brasilense wild type and mutant strains altered in IAA production on wheat

Auxin production by Azospirillum is believed to play a major role in the observed plant growth promoting effect. By using different genetically modified strains, the contribution of auxin biosynthesis by A. brasilense in altering root morphology was evaluated in a plate assay. Inoculation with the wild type strains A. brasilense Sp245 and Sp7 resulted in a strong decrease in root length and increase in root hair formation. This effect was abolished when inoculating with an ipdC mutant of A. brasilense. The ipdC gene encodes a key enzyme in the IPyA pathway of IAA synthesis by A. brasilense. On the other hand, the observed auxin effect was further enhanced by adding tryptophan, a precursor of IAA, to the plates and could be mimicked by replacing the Azospirillum cells by a particular concentration of IAA. Furthermore, particular mutants (rpoN, scrp) and transconjugants (extra copy of ipdC) of A. brasilense were tested in the plate assay. Together, these results confirm the important role of IAA produced by Azospirillum in altering root morphology and illustrate the power of combining genetic tools and bioassays to elucidate the mechanism of a beneficial Azospirillum-plant interaction. This revised version was published online in June 2006 with corrections to the Cover Date.     

小菜蛾幼虫偏好表达的microRNA鉴定及功能研究

[目的]microRNA(miRNA)在昆虫生长发育中发挥重要功能,本研究拟通过鉴定小菜蛾不同发育阶段的miRNA,挖掘幼虫偏好表达的miRNA及其潜在功能.[方法]对小菜蛾卵、3龄幼虫、蛹和成虫的miRNA开展高通量测序,结合生物信息学分析方法,筛选在幼虫期偏好表达的miRNA;借助实时荧光定量PCR技术,验证候选m...     

Rapid methods for quantifying VAM fungal infections in maize roots

Roots of maize (Zea mays cv W64A × W182E) infected by vesicular arbuscular mycorrhizal (VAM) fungi (Glomus versiforme (Karst) Berch or a Glomus species isolated from an alfalfa soil) exhibit a bright yellow pigmentation. The percentage of pigmented roots can be quantified by a rapid visual estimate or by a grid intersect method. Both methods gave similar estimates of VAM infection to those obtained using a grid intersect count on cleared roots stained with chlorazol black E. Thus for experimental or field evaluation where speed and quantity are important, the rapid visual estimate (less than one minute for each washed root system) yields reliable results. The yellow root intersect method takes longer (5–15 minutes per root system) but gives more reproducible results. The yellow root pigmentation is light sensitive However, root systems can be reliably assayed after 1 week when stored at 5°C in the dark or after 1 year if dried.     

Fine-root morphology and uptake of 32P and 35S in a Norway spruce (Picea abies (L.) Karst.) stand subjected to various nutrient and water supplies

An investigation of fine (< 1 mm in diameter) and small (1–2 mm in diameter) roots in the organic soil layer was carried out in a Norway spruce forest stand with different treatments of water and nutrients, including control (C); ammonium sulphate application (NS); nitrogen-free fertilization (V); irrigation with liquid fertilization (a complete nutrient solution) (IF); NS followed by artificial drought (ND); V followed by artificial drought (VD). In order to evaluate the vitality and function of the fine roots, the following approaches were used: i) classification of fine roots, based on morphological characteristics; ii) nutrient uptake bioassay, using ³²P-phosphate and ³⁵S-sulphate; iii) nutrient concentration in fine roots and its relation to nutrient uptake. The NS treatment showed effects on the fine and small roots, with a decrease in amount of living roots, and a decrease in the total amount of fine and small roots. The VD treatment resulted in increased amounts of living small roots, while the ND treatment showed the opposite, as compared with the V and NS treatments, respectively. The uptake of P was negatively related to the P supply, with a higher P uptake for C and NS fine roots than for IF and V fine roots. The specific root length (SRL, m g^-1 DW) decreased for NS fine roots and increased for IF fine roots, indicating a further increase in uptake for NS roots and a decreased uptake for IF roots if calculated on a root length basis. So far, the NS and IF treatments maintain a considerable increase in above-ground biomass with a significantly reduced root biomass and standing crop.     

An improved cage system for the bioassay of Metarhizium anisopliae on Thrips tabaci (Thysanoptera: Thripidae)

The ability of thrips and other minute insects to escape from conventional assay cups led to development of a successful assay chamber. In the present study, we evaluated three bioassay systems for thrips; Tashiro cage, microtube assay and leaf sandwich assay and introduced an improved thrips entomopathogenic bioassay system (TEBS). Our objective was to investigate the effect of Metarhizium anisopliae on Thrips tabaci using an easy-to-use and inexpensive holding chamber that would produce bioassay results with acceptable levels of accuracy and precision. In our assays, we found that escape of second-instar larvae from TEBS was significantly less than those of other methods which we tested. Our results indicated that our assay system was more suitable than the other conventional assays for the bioassay of entomopathogenic fungi on T. tabaci.     

Activity of delta-endotoxin protein crystals in Bacillus thuringiensis mutants when influenced by UV treatments

The ability of some isolates of Bacillus thuringiensis to produce dark brown pigment was measured as an indicator to UV resistance. M₅ as an indigenous Egyptian isolate was used as wild type to improve its resistance to UV. It was exposed to UV irradiation for different periods ranging between 1 and 10?h. The induced mutants were examined morphologically by phase contrast microscope. One hundred and forty four mutants were obtained; 10 of them were selected and tested for their toxicity against Spodoptera littoralis. The results showed that mutants 62, 65 and 85 were the most toxic ones. These three mutants and the wild type were examined by transmission electron microscope. Crystal proteins with bipyramidal shape and active against Lepidopteran insects were detected in all the selected mutants.