Insects had it first: surfactants as a defence against predators

Insects have evolved an astonishing array of defences to ward off enemies. Well known and widespread is the regurgitation of oral secretion (OS), fluid that repels attacking predators. In herbivores, the effectiveness of OS has been ascribed so far to the presence of deterrent secondary metabolites sequestered from the host plant. This notion implies, however, that generalists experience less protection on plants with low amounts of secondary metabolites or with compounds ineffective against potential enemies. Resolving the dilemma, we describe a novel defence mechanism that is independent of deterrents as it relies on the intrinsic detergent properties of the OS. The OS of Spodoptera exigua (and other species) was found to be highly amphiphilic and well capable of wetting the hydrophobic cuticle of predatory ants. As a result, affected ants stopped attacking and engaged in extensive cleansing. The presence of surfactants was sufficient to explain the defensive character of herbivore OS. We hypothesize that detergency is a common but unrecognized mode of defence, which provides a base level of protection that may or may not be further enhanced by plant-derived deterrents. Our study also proves that insects 'invented' the use of defensive surfactants long before modern agriculture had started applying them as insecticides.     

Replication licensing: oops! ... I did it again

All eukaryotes use multiple controls to restrict DNA replication to once per cell cycle. Nevertheless, inactivation of a single gene, cul-4, causes massive re-replication in Caenorhabditis elegans. A novel study explains this dramatic phenotype by demonstrating that the CUL-4 E3 ligase simultaneously controls two critical licensing factors: CDT-1 and CDC-6.     

Water hyacinth in Lake Victoria: Why did it vanish so quickly and will it return?

Water hyacinth has been a cause of great concern in terms of environmental and socio-economic impacts within Lake Victoria. In the late 1990s however it rapidly disappeared but since the causes are unknown its possible return cannot be predicted. Growth chamber and laboratory experiments investigating CO₂ assimilation and growth rate found that different phenotypic, density-acclimated, growth forms of water hyacinth behaved differently. PI-curves and changes in biomass revealed that short bulbous (SB) growth forms took up CO₂ more rapidly and increased in biomass quicker than tall non-bulbous (TN) growth forms. This allows the two growth forms to flourish within two different niches. One, the SB form, as a colonising opportunist and the other as a taller plant that attempts to avoid self-shading in dense mats. Light is an important limiting factor to water hyacinth growth. Light becomes non-limiting to CO₂ uptake at a PAR of ≈2000 μE m⁻² s⁻¹. In Lake Victoria this light level occurs for about 6 h around midday. Plant growth is thus light limited for most of the day and can be limited even at midday during cloudy weather. Although weevils likely played a role in the rapid disappearance of water hyacinth, its demise was too rapid and synchronous in this large lake for weevils to be solely responsible. The cloudy, wet El Nino weather of 1997/1998 was probably a major contributory factor to poor growth that led to the reduction in water hyacinth biomass lake-wide. Currently within Lake Victoria an improved light climate, an ever increasing supply of nutrients and a potentially unstable weevil population will likely allow the resurgence of this aggressive weed.     

Polysaccharide-based adhesive for biomedical applications: correlation between rheological behavior and adhesion

Adhesion to biological tissues is a challenge especially when the adhesive is in contact with physiological fluids. Abdominal hernia is a disease that often requires the implantation of a mesh within the abdominal wall. To minimize pain and postsurgical complications, gluing the mesh appears to be a convenient method. For this purpose, a bioadhesive system based on solutions of chitosan and modified starch (oxidized maltodextrin) has been developed. Mixtures of these polysaccharides form either viscoelastic solutions or hydrogels, depending on various experimental parameters (chitosan concentration, starch degree of oxidation, molar ratio between amine and aldehyde functions, pH, etc.). An adhesion test was developed to assess the adherence of such systems under conditions similar to the intended use. The rheological behavior of each formulation was correlated to its adherence, and it was found that optimum adhesion is obtained for systems exhibiting an intermediate behavior between the viscoelastic solution and the gel.     

Robust and sensitive nylon hybridization membrane suitable for high-throughput robotic arraying applications

An important aspect of automated macroarraying is the suitability of the nylon membrane selected on which samples are to be arrayed. PerForma is a positively charged nylon membrane that has been developed specificallyfor automated macroarraying. Tests usingfluorescent hybridization detection methods have shown that immobilized DNA amounts as low as 0.25 pg can be detected and that positive signals are obtainable after 21 stripping cycles. This report describes the improved colony growth, improved handling characteristics, increased hybridization detection sensitivity, and increased stripping and reprobing capability obtained using PerForma.     

Human upper-limb force capacities evaluation with robotic models for ergonomic applications: effect of elbow flexion

The aim of this study was to apply models derived from the robotics field to evaluate the human upper-limb force generation capacity. Four models were compared: the force ellipsoid (FE) and force polytope (FP) based on unit joint torques and the scaled FE (SFE) and scaled FP (SFP) based on maximum isometric joint torques. The four models were assessed from four upper-limb postures with varying elbow flexion (40°, 60°, 80° and 100°) measured by an optoelectronic system and their corresponding isometric joint torques. Ten subjects were recruited. Three specific ellipsoids and polytopes parameters were compared: isotropy, principal force orientation and volume. Isotropy showed that the ellipsoids and polytopes were elongated. The angle between the two ellipsoids main axis and the two polytopes remained low but increased with the elbow flexion. The FE and FP volumes increased and those of SFE and SFP decreased with the elbow flexion. The interest and limits of such models are discussed in the framework of ergonomics and rehabilitation.     

Insects on Hog weed Flowers: a Suggestion for a Student Project

The current Bullock debate has focused attention on the role of language in learning and challenges us to consider the linguistic competence of our pupils. This article describes how students' knowledge and interest in their own subject was used to start them thinking through ideas about language. For a group of biology graduates taking a postgraduate education course, biology became the vehicle for integrating more widely ranging educational issues.

After a preliminary introduction to the topic, opportunities were created for the students to gather school experience, and then in the light of this to extend their appreciation of available theory. The value of such an approach is discussed, and also the problems inherent in it, for example the division of tutorial responsibilities within the university department.     

Field site selection: getting it right first time around

The selection of suitable field sites for integrated control of Anopheles mosquitoes using the sterile insect technique (SIT) requires consideration of the full gamut of factors facing most proposed control strategies, but four criteria identify an ideal site: 1) a single malaria vector, 2) an unstructured, relatively low density target population, 3) isolation of the target population and 4) actual or potential malaria incidence. Such a site can exist in a diverse range of situations or can be created. Two contrasting SIT field sites are examined here: the desert-flanked Dongola Reach of the Nile River in Northern State, Sudan, where malaria is endemic, and the island of La Reunion, where autochthonous malaria is rare but risk is persistent. The single malaria-transmitting vector at both sites is Anopheles arabiensis. In Sudan, the target area is a narrow 500 km corridor stretching from the rocky terrain at the Fourth Cataract - just above the new Merowe Dam, to the northernmost edge of the species range, close to Egypt. Vector distribution and temporal changes in density depend on the Nile level, ambient temperature and human activities. On La Reunion, the An. arabiensis population is coastal, limited and divided into three areas by altitude and exposure to the trade winds on the east coast. Mosquito vectors for other diseases are an issue at both sites, but of primary importance on La Reunion due to the recent chikungunya epidemic. The similarities and differences between these two sites in terms of suitability are discussed in the context of area-wide integrated vector management incorporating the SIT.