Soil water flow affects the rhizosphere distribution of a seed-borne biological control agent,Pseudomonas fluorescens

Four-day-old wheat seedling roots were inoculated at specific sites with 3.8 × 10⁵ colony forming units of Pseudomonas fluorescens strain 2–79 Rn₁₀ resistant to rifampin and naladixic acid. Seedlings inoculated at the root apex were transplanted into chambers containing non-sterile soil and harvested 5 h, 2, 4 and 7 days later. Root segments were excised and processed for dilution plating on a selective medium to determine the population distribution of the marked strain in relation to root elongation. Strain 2–79 RN₁₀ was recovered from a localized area near the point of inoculation but was no longer associated with the root apex by day 4. In a subsequent experiment, roots were inoculated approximately 4 cm above the root tip. Water applied to the soil surface and allowed to drain through the soil profile was found to affect the rhizosphere distribution of 2–79 Rn₁₀. The marked strain was recovered 3.5 cm below the point of inoculation after 24 h when water had been added, compared to 0.5 cm below the inoculation site in the absence of added water.     

Significance of timing and level of inoculation with rhizosphere bacteria on wheat plants

The importance of time of inoculation and bacterial concentration in the inoculum on the response of wheat plants was evaluated, using eight strains of rhizosphere bacteria. The optimal bacterial concentration, for all strains, was 10⁵–10⁶ colony forming units ml⁻¹. Plant response was highest when seeds had been inoculated but was less when seedlings were inoculated. Successive inoculations somewhat increased plant response. Early inoculations resulted in an increased colonization of plant roots at later stages of growth. It was concluded that time of inoculation and the concentration of bacteria in the inoculum were of significant importance in plant response to inoculation and they may govern the inconsistency found in inoculation experiments using beneficial bacteria.     

Yolk sac absorption and early food selection in Atlantic salmon feeding on live prey

Six groups of Atlantic salmon (Salmo salar) fry were startfed with frozen Daphnia longispina, standard Ewos startfood or unfiltered live zooplankton drained from the littoral zone of a coastal lake. Through the last 5 days of the experiment, those fed live zooplankton were given additional food in the form of frozen Daphnia. Dry-fed groups were the only ones to have an overall weight gain but they had the lowest activity. Fry fed live zooplankton had the highest activity but the natural species composition of this food was not optimal for startfeeding. Survival was highest in the group fed frozen Daphnia and kept in a tank with bottom drainage. High yolk absorption rates, implying early termination of the yolk-sac phase, as found in groups fed live zooplankton, may be favourable if a net energy gain can be achieved by early feeding on a live prey.     

An eye disease in silver carp,Hypophthalmichthys molitrix,held in tropical ponds,associated with the bacterium Staphylococcus aureus

The occurrence of an eye disease in silver carp, Hypophthalmichthys molitrix, associated with a Gram-positive bacterium, Staphylococcus aureus, is described for the first time from India.     

The collection of early juveniles of Anadara spp. as a potential source of seed for culturing mangrove cockles on the Pacific coast of Colombia

Field observations were carried out to document the presence of early juveniles of Anadara spp. in a mangrove forest area of the Buenaventura Bay, Colombia, and to describe the seasonality of spat settlement. The effectiveness of several collection methods to obtain spat and juveniles on intertidal and subtidal mudflats was tested. Coconut husk collectors placed horizontally on subtidal mudflats were the only type that proved effective. A range of sizes of juveniles was obtained every month, but juveniles smaller than 3.0 mm in length were most frequent. It is suggested that Anadara spp. settle on a variety of surfaces in the subtidal zone, and migrate before recruiting to the adult population in the intertidal zone.     

Characterization of a Trans-permethrin hydrolyzing enzyme from the midgut of Pseudoplusia includens (Walker)

The enzymatic hydrolysis of trans-permethrin by midgut homogenates of the soybean looper, Pseudoplusia includens (Walker), was characterized through gel electrophoresis, isoelectric focusing, gel filtration chromatography, and selective inhibition. All three separation techniques indicated that one enzyme (or closely related enzyme forms) was responsible for the observed hydrolytic activity. The molecular weight was approximately 80,000, the isoelectric point ranged from pH 4.6 to 4.8, and the apparent K_m was 59.5 ± 3.2 μM. Enzyme activity was inhibited by organophosphates, carbamates, and sulfhydryl group inhibitors, as well as some chelators. The hydrolysis of trans-permethrin was distinct from the majority of “general esterase” activity when enzyme activity was separated by electrophoretic techniques.     

Insecticide metabolism by multiple glutathione S-transferases in two strains of the house fly,Musca domestica (L)

Glutathione S-transferases from two strains of house fly have been prepared in a high degree of homogeneity by a procedure involving affinity chromatography and isoelectrofocusing. They fall into two groups in each strain. One group, of isoelectric point greater than pH 6.5, catalyzes the glutathione-dependent degradation of lindane, diazinon and methyl parathion. The other group, of low isoelectric point, has conjugating activity with the model substrate CDNB, but very little activity with the insecticide substrates. In the Cornell R strain the three isoenzyme forms in the high pI group appear to be almost identical in their substrate specificities. In the A strain, it is apparent that the enzyme forms falling into this group vary markedly in substrate specificity. The dehydrochlorination of DDT paralleled very closely the conjugation of the other insecticides catalyzed by the three high pI enzymes in the Cornell R strain. In the A strain, DDT dehydrochlorinase was most strongly associated with a glutathione S-transferase isoelectric at pH 7.1. It is tentatively concluded that multiple genes are involved in the production of the glutathione S-transferases involved in pesticide metabolism in the house fly and that DDT dehydrochlorinase may be derived from some, but not all, of these same genes.     

The toxic action of Bacillus thuringiensis var. israelensis in Aedes aegypti in vivo: II. The relevance of skeletal muscle system lesions to its poisoning syndrome

Skeletal muscles of Aedes aegypti larva undergo progressive structural damage following ingestion of Bacillus thuringiensis var. israelensis crystal toxin (BTI). In BTI-treated mosquito larvae, skeletal muscles swell, the plasma membrane separates from underlying myofibrils, and mitochondria lose their structural integrity. With the progress of poisoning, BTI-induced damage extends to A-bands and I-bands. BTI treatment also impairs skeletal myoepidermal cells. The time of appearance and intensity of ultrastructural lesions in the skeletal muscle system coincides with the onset of overt symptoms of BTI poisoning such as sluggishness and general body paralysis. The results of this study indicate that the skeletal muscle system plays a major role in symptomatic manifestation of BTI toxicity. The necrosis of skeletal muscles appears to be the principal cause of paralysis in BTI-treated insects.     

A computer-based advisory system for cereal aphid control

The development of research on cereal aphid damage to winter wheat is described, from early field-cage work on Sitobion avenae through a research simulation model to the development of a computer-based Viewdata advisory system for cereal aphid control. Aphid control decisions in the U.K. have frequently been irrational and uneconomic in the past and appear still to be based on inadequate information. A dynamic advisory package based on the economics of insecticide application and the aphid yield loss/growth stage relationship has been developed for ‘Farmlink’ subscribers on ‘Prestel’, British Telecommunications' Viewdata service.