Advantages of larval control for African malaria vectors: Low mobility and behavioural responsiveness of immature mosquito stages allow high effective coverage

Background  

Based on sensitivity analysis of the MacDonald-Ross model, it has long been argued that the best way to reduce malaria transmission is to target adult female mosquitoes with insecticides that can reduce the longevity and human-feeding frequency of vectors. However, these analyses have ignored a fundamental biological difference between mosquito adults and the immature stages that precede them: adults are highly mobile flying insects that can readily detect and avoid many intervention measures whereas mosquito eggs, larvae and pupae are confined within relatively small aquatic habitats and cannot readily escape control measures.     

Interferometric analysis of intrasection and intersection thickness variability associated with cryostat microtomy

Summary Mach-Zehnder interferometric measurements were used to assess the extent of section thickness variability (inter- and intrasection) associated with cryostat microtomy of adrenal sections over a typical working range of 10–20 m. Sections were obtained using a Bright's Cambridge rocking type and a Damon rotary type cryostat microtome to allow comparative analyses. The effective thickness of tissue sections after being mounted onto slides by flash drying was reduced by 90% relative to microtome section thickness setting. A linear relationship between measured thickness and microtome setting was obtained with both instruments. Thickness variability between replicate sections over the range of microtome settings approximated 11% for the rocking microtome and 5% with the rotary microtome. Average intrasection variability was found to be 7% for rocking microtome sections and 4% for sections obtained with the rotary microtome. However, this variability is a negligible source of error in cytophotometric analyses, providing replicate sections are used and an adequate number of measurements are made on mask-delimited individual cells or tissue specimen areas.     

Radiation biology of mosquitoes

There is currently renewed interest in assessing the feasibility of the sterile insect technique (SIT) to control African malaria vectors in designated areas. The SIT relies on the sterilization of males before mass release, with sterilization currently being achieved through the use of ionizing radiation. This paper reviews previous work on radiation sterilization of Anopheles mosquitoes. In general, the pupal stage was irradiated due to ease of handling compared to the adult stage. The dose-response curve between the induced sterility and log (dose) was shown to be sigmoid, and there was a marked species difference in radiation sensitivity. Mating competitiveness studies have generally been performed under laboratory conditions. The competitiveness of males irradiated at high doses was relatively poor, but with increasing ratios of sterile males, egg hatch could be lowered effectively. Males irradiated as pupae had a lower competitiveness compared to males irradiated as adults, but the use of partially-sterilizing doses has not been studied extensively. Methods to reduce somatic damage during the irradiation process as well as the use of other agents or techniques to induce sterility are discussed. It is concluded that the optimal radiation dose chosen for insects that are to be released during an SIT programme should ensure a balance between induced sterility of males and their field competitiveness, with competitiveness being determined under (semi-) field conditions. Self-contained ⁶⁰Co research irradiators remain the most practical irradiators but these are likely to be replaced in the future by a new generation of high output X ray irradiators.     

Confirmation of quantitative trait loci affecting fatness in chickens

In this report we describe the analysis of an advanced intercross line (AIL) to confirm the quantitative trait locus (QTL) regions found for fatness traits in a previous study. QTL analysis was performed on chromosomes 1, 3, 4, 15, 18, and 27. The AIL was created by random intercrossing in each generation from generation 2 (G₂) onwards until generation 9 (G₉) was reached. QTL for abdominal fat weight (AFW) and/or percentage abdominal fat (AF%) on chromosomes 1, 3 and 27 were confirmed in the G₉ population. In addition, evidence for QTL for body weight at the age of 5 (BW5) and 7 (BW7) weeks and for the percentage of intramuscular fat (IF%) were found on chromosomes 1, 3, 15, and 27. Significant evidence for QTL was detected on chromosome 1 for BW5 and BW7. Suggestive evidence was found on chromosome 1 for AFW, AF% and IF%, on chromosome 15 for BW5, and on chromosome 27 for AF% and IF%. Furthermore, evidence on the chromosome-wise level was found on chromosome 3 for AFW, AF%, and BW7 and on chromosome 27 for BW5. For chromosomes 4 and 18, test statistics did not exceed the significance threshold.     

Quantifying the relationship between disease severity and the amount of Aphanomyces euteiches detected in roots of alfalfa and pea with a real-time PCR assay

A real-time PCR assay was used to quantify the relationship in alfalfa and pea between disease severity and the amount of Aphanomyces euteiches detected in roots. The study included isolates of race 1 and race 2 of the alfalfa pathovar of A. euteiches and an isolate obtained from diseased pea. Spearman rank correlations between pathogen DNA content and disease severity index (DSI) ratings were positive ( ? 0.57) and significant (P  0.0007) for individual alfalfa plants, bulked alfalfa plant samples, and individual pea plants. In all experiments, significantly more pathogen was detected in susceptible populations than in resistant populations. The results clearly demonstrate that resistance to A. euteiches in both alfalfa and pea is characterized by a reduction in pathogen colonization relative to levels observed for susceptible reactions. The assay was very specific for A. euteiches, producing very linear assays with DNA extracted from pathogen isolates obtained from alfalfa, pea, and bean. Possible applications of the assay in conjunction with other real-time PCR assays specific to other legume pathogens are discussed in relation to simultaneous disease screening for multiple plant pathogens and the study of microbial population dynamics in mixed plant infections.     

Single-molecule anisotropy imaging

A novel method, single-molecule anisotropy imaging, has been employed to simultaneously study lateral and rotational diffusion of fluorescence-labeled lipids on supported phospholipid membranes. In a fluid membrane composed of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, in which the rotational diffusion time is on the order of the excited-state lifetime of the fluorophore rhodamine, a rotational diffusion constant, D(rot) = 7 x 10(7) rad(2)/s, was determined. The lateral diffusion constant, measured by direct analysis of single-molecule trajectories, was D(lat) = 3.5 x 10(-8) cm(2)/s. As predicted from the free-volume model for diffusion, the results exhibit a significantly enhanced mobility on the nanosecond time scale. For membranes of DPPC lipids in the L(beta) gel phase, the slow rotational mobility permitted the direct observation of the rotation of individual molecules characterized by D(rot) = 1.2 rad(2)/s. The latter data were evaluated by a mean square angular displacement analysis. The technique developed here should prove itself profitable for imaging of conformational motions of individual proteins on the time scale of milliseconds to seconds.     

Caerulein secretion by dermal glands in xenopus laevis

Since gastrin and its related peptides are secreted by a minority population of widely dispersed cells in mamamalian tissues it has, in the past, been difficult to study the subcellular aspects of their secretion. From published reports (1, 2) it seemed possible that a satisfactory system for such studies might be provided by the skin of certain amphibians such as Xenopus laevis since in these tissues high concentrations of peptides such as caerulein exist, and there is some indication (3) that this, or a similar gastrin-like peptide, may be a dermal gland secretory product. We have therefore explored this possibility by studying the structure, secretory process, and secretory product of the most prominent non mucous type of gland in the skin of X. laevis. These studies clearly demonstrate that most, if not all, of the caerulein in which the skin is contained in secretion granules within the dermal glands and that its release can be specifically evoked by adrenergic stimulation. The release process by a holocrine mechanism expels all of the stored secretion onto the skin surface and thus for biosynthetic studies it should now be possible to synchronize the processes which lead to the replenishment of the peptide.