Specialisation of bacterial endosymbionts that protect aphids from parasitoids

1. Infection by the bacterial endosymbiont Hamiltonella defensa is capable of protecting the pea aphid from parasitism by Aphidius ervi and the black bean aphid from parasitism by Lysiphlebus fabarum. Here we investigate protection of a third aphid species, the cowpea aphid, Aphis craccivora, from four parasitoid species: Binodoxys communis, B. koreanus, Lysiphlebus orientalis, and Aphidius colemani. 2. We compared parasitism of A. craccivora lines that were either infected with, or cured of H. defensa separately for the four parasitoid species. Infection by H. defensa almost completely eliminated parasitism of A. craccivora by B. communis and B. koreanus, but had no effect on parasitism by L. orientalis and A. colemani. 3. This indicates at least genus‐level specificity of protective effects by H. defensa and we discuss implications of our findings on the known world‐wide distribution of this host/symbiont interaction.     

A technique for measuring the susceptibility of wheat bulb fly larvae to insecticides in the laboratory

A simple assay is described for measuring the toxicity of insecticides to larvae of wheat bulb fly (Delia coarctata) in the laboratory. The method should be suitable for other small soil insect larvae that cannot be obtained in large numbers and are difficult to treat and confine. A limitation of the technique is that it works only with insecticides that are soluble enough to be toxic in aqueous solution.     

A COMPUTERIZED SYSTEM FOR CONTROLLING AND MEASURING GUSTATORY REACTION TIMES

Reaction Time (RT) procedures are widely used in cognitive and behavioral experiments. In the sensory realm RT has been traditionally applied to measure visual, auditory or motor responses. The application of the RT method to gustatory stimuli has proved to be difficult. Attempts to develop automatic control techniques have been restrained by difficulties related to the control of variables, e.g. physiochemical characteristics of chemical solutions and the procedure for stimulus presentation. In this report we describe a computer based system that was designed to measure the reaction time to taste solutions dropped on the tongue. The equipment consists of a pumping system, an interface between the computer and the pumping system, the software required to control the interface and to measure reaction time, and a push button to detect the subject's response. The system can be used as a tool for both research and evaluation tests.     

Static and dynamic bending has minor effects on xylem hydraulics of conifer branches (Picea abies,Pinus sylvestris)

The xylem hydraulic efficiency and safety is usually measured on mechanically unstressed samples, although trees may be exposed to combined hydraulic and mechanical stress in the field. We analysed changes in hydraulic conductivity and vulnerability to drought‐induced embolism during static bending of Picea abies and Pinus sylvestris branches as well as the effect of dynamic bending on the vulnerability. We hypothesized this mechanical stress to substantially impair xylem hydraulics. Intense static bending caused an only small decrease in hydraulic conductance (?19.5 ± 2.4% in P. abies) but no shift in vulnerability thresholds. Dynamic bending caused a 0.4 and 0.8 MPa decrease of the water potential at 50 and 88% loss of conductivity in P. sylvestris, but did not affect vulnerability thresholds in P. abies. With respect to applied extreme bending radii, effects on plant hydraulics were surprisingly small and are thus probably of minor eco‐physiological importance. More importantly, results indicate that available xylem hydraulic analyses (of conifers) sufficiently reflect plant hydraulics under field conditions.     

Further Studies on the Suitability of Various Media Containing Antibacterial Antibiotics for the Enumeration of Moulds in Food and Food Environments

Oxytetracycline–glucose–yeast extract agar (OGYA), gentamicin–glucose–yeast extract agar (GGYA) with the antibiotic added separately or sterilized with the medium, chlortetracycline–Rose Bengal agar (CRA), chloramphenicol-streptomycin agar (PYA) and to a lesser extent, oxytetracycline–gentamicin–glucose–yeast extract agar (OGGYA) with or without Rose Bengal added, have been compared for the selective enumeration of moulds in foods. The results obtained from dried cereal products show that the media are almost equally productive and selective when applied to such foods, but Rose Bengal limits the size of mould colonies. When examining fresh proteinaceous foods, such as minced meat and chicken, CR agars and to a certain extent gentamicin-containing agars show the distinct advantage of being much more inhibitory towards the psychrotrophic Gram negative rods that predominate in the associated flora of such foods. Oxytetracycline–glucose–yeast extract agar lost its bacteriostatic properties when heavily challenged with proteinaceous substrates and/or incubated for longer periods at 37° or even at 25°. For such applications chloramphenicol was found to be the antibiotic of choice.