Poor survival on an artificial diet of two genotypes of the aphid Myzus persicae: a fitness cost of insecticide resistance?

1. A fully susceptible genotype (4106A) of Myzus persicae survived the longest on an artificial diet and, in several of the eight replicates, monitoring was terminated when the culture was still thriving. A genotype with elevated carboxylesterase FE4 at the R₃ level (800F) had a mean survival of only 98.13 days, whereas 794J, which combines R₃ E4 carboxylesterase with target‐site resistance (knockdown resistance), survived for the even shorter mean time of 84.38 days.
2. The poorer survival of the two genotypes with extremely elevated carboxylesterase‐resistance was not the result of a reluctance to transfer to new diet at each diet change.
3. Although available for only two replicates, a revertant clone of 794J (794Jrev), which has the same genotype as 794J but the amplified E4 genes are not expressed leading to a fully susceptible phenotype, did not appear to survive any better than this clone. This suggests that the poor survival on an artificial diet of the extreme‐carboxylesterase genotypes is not the result of the cost of over‐producing the enzyme.
4. The frequency of insecticide‐resistant genotypes is low in the population until insecticide is applied, indicating that they have reduced fitness, although this does not necessarily reflect a direct cost of expressing the resistance mechanism.

     

Studies on the artificial feeding of the aphid Myzus persicae (Sulzer)—I. Relative uptake of water and sucrose solutions

A method is described for feeding the green peach aphid Myzus persicae (Sulzer) on liquids accessible via artificial membranes of stretched Parafilm ‘M’^(R). The aphids ingest considerable amounts of water and sugary fluids entirely by their own sucking efforts. A simple colour scoring method is described which is convenient for routinely assessing the relative uptake by the aphids of various diets. The numbers and kinds of salivations produced by the aphids when penetrating and feeding through membranes are related to the amount of liquid imbibed. The numbers of larvae born to adult apterous aphids are dependent on both the amount of fluid imbibed and its composition. Probing and associated feeding behaviour under the artificial feeding conditions is discussed in relation to the normal feeding behaviour of aphids on their host plants. On the basis of the different criteria of uptake considered in this study, sucrose is distinctly phagostimulatory to M. persicae, 10 to 20 per cent being the optimal concentration range.     

Does insecticide resistance alone account for the low genetic variability of asexually reproducing populations of the peach-potato aphid Myzus persicae?

The typical life cycle of aphids includes several parthenogenetic generations and a single sexual generation (cyclical parthenogenesis), but some species or populations are totally asexual (obligate parthenogenesis). Genetic variability is generally low in these asexually reproducing populations, that is, few genotypes are spread over large geographic areas. Both genetic drift and natural selection are often invoked to account for this low genetic variability. The peach-potato aphid, Myzus persicae, which encompasses both cyclical and obligate parthenogens, has developed several insecticide resistance mechanisms as a consequence of intense insecticide use since the 1950s. We collected asexually reproducing M. persicae from oilseed rape and examined genetic variability at eight microsatellite loci and three insecticide resistance genes to determine whether their genetic structure was driven by drift and/or selection. We identified only 16 multilocus microsatellite genotypes among 255 individuals. One clone, which combined two insecticide resistance mechanisms, was frequently detected in all populations whatever their location over a large geographical area (the northern half of France). These unexpected findings suggest that drift is not the unique cause of this low variability. Instead, the intensification of both insecticide treatments and oilseed rape cultivation may have favored a few genotypes. Thus, we propose that selective pressures resulting from human activities have considerably modified the genetic structure of M. persicae populations in northern France in a relatively short period of time.     

Can invasions occur without change? A comparison of G-matrices and selection in the peach-potato aphid,Myzus persicae

Most evolutionary research on biological invasions has focused on changes seen between the native and invaded range for a particular species. However, it is likely that species that live in human‐modified habitats in their native range might have evolved specific adaptations to those environments, which increase the likelihood of establishment and spread in similar human‐altered environments. From a quantitative genetic perspective, this hypothesis suggests that both native and introduced populations should reside at or near the same adaptive peak. Therefore, we should observe no overall changes in the G (genetic variance–covariance) matrices between native and introduced ranges, and stabilizing selection on fitness‐related traits in all populations. We tested these predictions comparing three populations of the worldwide pest Myzus persicae from the Middle East (native range) and the UK and Chile (separately introduced ranges). In general, our results provide mixed support for this idea, but further comparisons of other species are needed. In particular, we found that there has been some limited evolution in the studied traits, with the Middle East population differing from the UK and Chilean populations. This was reflected in the structure of the G ‐matrices, in which Chile differed from both UK and Middle East populations. Furthermore, the amount of genetic variation was massively reduced in Chile in comparison with UK and Middle East populations. Finally, we found no detectable selection on any trait in the three populations, but clones from the introduced ranges started to reproduce later, were smaller, had smaller offspring, and had lower reproductive fitness than clones from the native range.     

Halophytes – A resource for the future

Wetlands Ecology and Management -     

Annotated expressed sequence tags and xenobiotic detoxification in the aphid Myzus persicae （Sulzer）

Aphids （Hemiptera： Aphididae） are phytophagous insects that are important agricultural pests. The enormous negative economic impacts caused by aphids worldwide are well known, and are mostly due to their high multiplication rate and the transmission of phytopathogenic viruses. Aphid management strategies mainly involve chemical treatments which are pollutants and are increasingly inefficient, since aphids have developed multiple insecticide-resistant mechanisms. Among the most economically important species is the green peach aptfid Myzus persicae Sulzer （Aphididae： Macrosiphini）, which is able to colonize a wide range of host plants belonging to many different families, and transmits numerous plant viruses. Because of its large prevalence, M. persicae has been the target of massive insecticide treatments; consequently, it has evolved several insecticide-resistant mechanisms. In this work, a collection of expressed genes from M. persicae is presented in order to identify putative genes involved in xenobiotic detoxification. After cDNA cloning and sequencing, 959 expressed sequence tags （EST） were annotated. Most sequences matched known genes corresponded to metabolism proteins （26%）, ribosomal proteins （ 23 % ） and structural proteins （8%）. Among them, several sequences corresponded to proteins putatively involved in sensing, degradation or detoxification of plant xenobiotic products.     

The rôle of folic acid in the appearance of alate forms in Myzus persicae

The rôle of folic acid in wing formation was studied using amino-pterin—a folic acid antagonist. The effects of this antivitamin are acute: larviposition ceases in adults and wing formation is depressed in developing larvae. At lower concentrations graded responses are obtained. Omission of methionine and histidine had no effect on wing formation but thymidine did ameliorate the depression of wing formation by aminopterin.Aminopterin is known to inhibit dihydrofolate reductase—thereby inhibiting tetrahydrofolate production. Tetrahydrofolate is known to be involved in thymidine biosynthesis. The activity of dihydrofolate reductase in presumptive alates was 42 per cent higher than in larvae destined to develop as apterates. The significance of folic acid metabolism in wing formation is discussed.     

Science – A life fully lived: Joe Sodroski wins the 2006 Retrovirology Prize

The 2006 M Jeang Retrovirology Prize for HIV research has been awarded to Dr Joe Sodroski     

Super-CHO—A cell line capable of autocrine growth under fully defined protein-free conditions

Chinese Hamster Ovary (CHO) cells are widely used for the large scale production of recombinant biopharmaceuticals. Growth of the CHO-K1 cell line has been demonstrated in serum-free medium containing insulin, transferrin and selenium. In an attempt to get autocrine growth in protein-free medium, DNA coding for insulin and transferrin production was transfected into CHO-K1 cells. Transferrin was expressed well, with clones secreting approximately 1000 ng/10⁶ cells/24h. Insulin was poorly expressed, with rates peaking at 5 ng/10⁶ cells/24h. Characterisation of the secreted insulin indicated that the CHO cells were incompletely processing the insulin molecule. Site-directed mutagenesis was used to introduce a furin (prohormone converting enzyme) recognition sequence into the insulin molecule, allowing the production of active insulin. However, the levels were still too low to support autocrine growth. Further investigations revealed insulin degrading activity (presumably due to the presence of insulin degrading enzymes) in the cytoplasm of CHO cells. To overcome these problems insulin-like growth factor I (instead of insulin) was transfected into the cells. IGF-1 was completely processed and expressed at rates greater than 500 ng/10⁶cells/24h. In this paper we report autonomous growth of the transfected CHO-K1 cell line expressing transferrin and IGF-1 in protein-free medium without the addition of exogenous growth factors. Growth rates and final cell densities of these cells were identical to that of the parent cell line CHO-K1 growing in insulin, transferrin, and selenium supplemented serum-free media.     

Phototactic behaviour of Pachyneuron aphidis (Hymenoptera: Pteromalidae) – hyperparasitoid of Myzus persicae (Hemiptera: Aphidiae)

We investigated the spectral sensitivity and response to light intensity of Pachyneuron aphidis (Hymenoptera: Pteromalidae), which is a common hyperparasitoid of Aphidius gifuensis (Hymenoptera: Braconidae), a key natural enemy of the green peach aphid, Myzus persicae (Hemiptera: Aphididae). To do so, we used 15 monochromatic lights (emitting various specific wavelengths from 340 to 649 nm) and white light. P. aphidis adults are diurnal insects that show a positive phototaxis to a broad spectrum of light. Significant differences were found between sexes in the phototactic responses of P. aphidis to different monochromatic lights. Female P. aphidis showed four peaks of sensitivity at 380, 450, 504 and 589 nm. Male P. aphidis show two peaks of sensitivity, one at 450 nm and second at 628 nm. P. aphidis adults showed an increased phototactic response at low intensities and a decreased phototactic response at high intensities for both UV light and blue light. This experiment will help provide a scientific basis for the development of colour traps for insect pest management.     

A superior drug carrier – aponeocarzinostatin in partially unfolded state fully protects the labile antitumor enediyne

Background  

Neocarzinostatin is a potent antitumor drug consisting of an enediyne chromophore and a protein carrier.     

Effect of temperature,relative humidity and aphid developmental stage on the efficacy of the mycoinsecticide Mycotal® against Myzus persicae

The green peach aphid, Myzus persicae, is a major pest worldwide. An examination of the impact of temperature, relative humidity (RH) and developmental stages of M. persicae on the efficacy of the whitefly mycoinsecticide Mycotal®, based on Lecanicillium muscarium and the effects of infection on aphid fecundity was evaluated under controlled conditions. Although this fungus can be grown at a broad range of temperatures (15–30°C), the optimum temperature for control of M. persicae ranged between 20 and 30°C. L. muscarium had high efficacy as a microbial control agent against M. persicae between 55% and 90% RH. Total mortality of aphids treated with different spore dosages of L. muscarium varied according to the developmental stage: adults, fourth and third instar nymphs proved more susceptible than first instar nymphs. Although the fungus did not affect the rate of nymph production, the reproductive period of aphids significantly decreased with increasing the spore dosage. Thus, total fecundity of treated aphids was 22.6 ± 1.1 and 31.6 ± 2.4 offspring per adult at the medium (644 ± viable spore/mm²) and low (330 ± 40 viable spore/mm²) dosages, compared with 45.7 ± 4.3 offspring per untreated aphid. The results suggest that L. muscarium has the potential as a biological control agent of M. persicae.     

Mapping Rm2 gene conferring resistance to the green peach aphid (Myzus persicae Sulzer) in the peach cultivar ��Rubira?��

The green peach aphid (GPA), Myzus persicae (Sulzer), is a widespread pest insect that significantly reduces yield in peach orchards [Prunus persica (L.) Batsch]. Chemical control of the GPA population in the orchards showed little efficiency because of the development of resistance to most classes of insecticides. Biological control partially gave convincing results. Breeding for resistant peach cultivars is therefore a serious option to take into account for the development of sustainable pest management. Among the few available resistance cultivars, the rootstock peach “Rubira?” shows a strong induced antixenosis-type GPA resistance. This was demonstrated segregating as a single dominant gene. In order to investigate the genetic basis of resistance and develop molecular tools useful in breeding programs, a F₂ population derived from “Rubira?” also segregating for leaf color was grown and scored for GPA resistance under contrasted environmental conditions. An SSR-based genetic linkage map composed of 120 SSR loci spanned over a distance of 497.8 cM was then established. The GPA resistance mapped to a single locus at the bottom end of linkage group 1. We propose to name Rm2 the dominant allele of the underlying gene. Additionally, a reciprocal translocation was identified near the Gr gene controlling leaf color. The red-leaf parent “Rubira?” was demonstrated responsible for the translocation. This study provides the basis for future molecular analysis for the use of Rm2 in peach breeding programs against GPA in peach orchards.     

A System of Two Polymerases – A Model for the Origin of Life

What was the first living molecule – RNA or protein?This question embodies the major disagreement instudies on the origin of life. The fact that incontemporary cells RNA polymerase is a protein andpeptidyl transferase consists of RNA suggests theexistence of a mutual catalytic dependence betweenthese two kinds of biopolymers. I suggest that thisdependence is a `frozen accident', a remnant from thefirst living system. This system is proposed to be acombination of an RNA molecule capable of catalyzingamino acid polymerization and the resulting proteinfunctioning as an RNA-dependent RNA polymerase. Thespecificity of the protein synthesis is thought to beachieved by the composition of the surrounding mediumand the specificity of the RNA synthesis – by Watson– Crick base pairing. Despite its apparent simplicity,the system possesses a great potential to evolve intoa primitive ribosome and further to life, as it isseen today. This model provides a possible explanationfor the origin of the interaction between nucleicacids and protein. Based on the suggested system, Ipropose a new definition of life as a system ofnucleic acid and protein polymerases with a constantsupply of monomers, energy and protection.     

Mapping of the 3′ end for artificial human microRNAs

The 3?? end was exactly mapped for has-mir-30a-like artificial human microRNAs that specifically recognize the mRNA of the aml1/eto fusion oncogene. The results indicated that the intracellular microRNA pool was heterogeneous in linear size relative to the 3?? end, which is necessary to consider in designing and using artificial microRNAs specific for mRNAs of other genes.     

How important is the statistical approach for analyzing categorical data? A critique using artificial nests

Ecologists rely heavily upon statistics to make inferences concerning ecological phenomena and to make management recommendations. It is therefore important to use statistical tests that are most appropriate for a given data-set. However, inappropriate statistical tests are often used in the analysis of studies with categorical data (i.e. count data or binary data). Since many types of statistical tests have been used in artificial nests studies, a review and comparison of these tests provides an opportunity to demonstrate the importance of choosing the most appropriate statistical approach for conceptual reasons as well as type I and type II errors.
Artificial nests have routinely been used to study the influences of habitat fragmentation, and habitat edges on nest predation. I review the variety of statistical tests used to analyze artificial nest data within the framework of the generalized linear model and argue that logistic regression is the most appropriate and flexible statistical test for analyzing binary data-sets. Using artificial nest data from my own studies and an independent data set from the medical literature as examples, I tested equivalent data using a variety of statistical methods. I then compared the p-values and the statistical power of these tests. Results vary greatly among statistical methods. Methods inappropriate for analyzing binary data often fail to yield significant results even when differences between study groups appear large, while logistic regression finds these differences statistically significant. Statistical power is is 2–3 times higher for logistic regression than for other tests. I recommend that logistic regression be used to analyze artificial nest data and other data-sets with binary data.     

A manual method for reducing sugar determinations with 2,2′-bicinchoninate reagent

A method was developed to analyze reducing sugars manually by use of a 2,2′-bicinchoninate reagent. Potassium phosphate was used to buffer the reagent. Ethylene glycol increased the sensitivity of the assay for several sugars. Sugar determinations can be performed in the presence of borate ion. In comparative assays of a number of monosaccharides and disaccharides, the bicinchoninate reagent was about as sensitive as the Nelson reagent but more convenient to use. The effects of ethylene glycol concentration, reagent pH, heating time, and borate ion on color development were evaluated.     

Hydrophilicity Matching – A Potential Prerequisite for the Formation of Protein-Protein Complexes in the Cell

A binding event between two proteins typically consists of a diffusional search of binding partners for one another, followed by a specific recognition of the compatible binding sites resulting in the formation of the complex. However, it is unclear how binding partners find each other in the context of the crowded, constantly fluctuating, and interaction-rich cellular environment. Here we examine the non-specific component of protein-protein interactions, which refers to those physicochemical properties of the binding partners that are independent of the exact details of their binding sites, but which can affect their localization or diffusional search for one another. We show that, for a large set of high-resolution experimental 3D structures of binary, transient protein complexes taken from the DOCKGROUND database, the binding partners display a surprising, statistically significant similarity in terms of their total hydration free energies normalized by a size-dependent variable. We hypothesize that colocalization of binding partners, even within individual cellular compartments such as the cytoplasm, may be influenced by their relative hydrophilicity, potentially in response to local hydrophilic gradients.