Parasitoid behaviour: predicting field from laboratory

Abstract.  1. Most of what is known about parasitoid behaviour comes from laboratory observations: field quantitative observations on searching parasitoids are extremely difficult to do and are rare. The basic components of Aphytis melinus 's response to California red scale ( Aonidiella aurantii ) were studied in the laboratory: encounter, rejection, drumming, probing, oviposition, and host-feeding. It was then asked whether these observations provided a reliable guide to behaviour in the field in a situation that was very different from the laboratory.
2. Field observations were carried out on bark on the trunk and interior branches of trees where live scale density is extremely high in patches, dead scale make up 90% of all scale, and could be expected to interfere with Aphytis search.
3. The laboratory observations predicted well the time taken in the field for each basic event (drumming or probing) and average times spent on a scale. Also well predicted were the distributions of times spent on drumming, probing, and total time on a scale. Rejection rates were much higher in the field. Thus, the laboratory studies predicted foraging behaviour in the field with variable success; potential explanations for observed mismatch between laboratory and field and its possible larger implications are discussed.     

Is male back space limiting? An investigation into the reproductive demography of the giant water bug,Abedus indentatus (Heteroptera: Belostomatidae)

Because male giant water bugs in the subfamily Belostomatinae provide parental care by brooding eggs on their back, an accurate assessment can be made of both the actual and potential reproductive capacity of males. Two operational sex-ratio (OSR) indices were developed and empirically measured for a population of giant water bug, Abedus indentatus,in California. One index was based on reproductive rates measured in the laboratory; the other index was based on reproductive resources observed in the field. Both OSR indices suggest that the operational sex ratio fluctuates between maleskewed ratios in the summer and femaleskewed ratios in the winter. This pattern appears to be the consequence of two factors. First, the adult sex ratio is significantly female biased. Second, although males can outreproduce females at high ambient temperatures, the reverse is true at low temperatures. Possible reasons for the female-skewed adult sex ratio are examined, including differential recruitment, differential mortality, and sampling bias.     

The effect of cycloheximide on Euglena gracilis phenylalanyl-tRNA synthetases

The effect of cycloheximide on the chloroplastic, cytoplasmic and mitochondrial phenylalanyltransferRNA synthetases of Euglena gracilis was studied by growing both logarithmic and stationary phase cultures in the presence of the antibiotic. Enzyme activity was measured relative to untreated control cultures. At very low concentrations of cycloheximide (1 g/ml), all three log phase enzymes showed an increase in activity of 40–50%. At slightly higher concentrations (2.5 g/ml), the phenylalanyl-tRNA synthetase activities were comparable to those of the control cultures. At a cycloheximide concentration of 5g/ml the enzyme activities from stationary phase cultures showed only very slight decreases (5–20%). The cytoplasmic and mitochondrial enzymes behaved similarly in log phase cultures at this concentration. However, the chloroplastic phenylalanyl-tRNA synthetase from log phase cultures treated with 5g/ml cycloheximide showed a marked decrease in activity (70%). A further increase in antibiotic concentration to 10g/ml resulted in significant losses of activity of all three enzymes, from both growth stages. The implications of the data with regard to identification of the site(s) of chloroplast enzyme synthesis are discussed.     

Bahavioral fever in crayfish

Crayfish (Cambarus bartoni) were tested individually in an electronic shuttlebox thermoregulatory device which allowed them to control water temperature, and thereby their body temperature, by their movements.Crayfish which initially selected 22.1°C water increased their preferred temperature by 1.8°C following injection of killed bacteria (Aeromonas hydrophila) into the gill cavity.This behavioral fever appears similar to that of vertebrates, and may enhance host defense reactions against pathogens.     

Occurrence,localization, and possible significance of an ornithine-containing lipid in Paracoccus denitrificans

A ninhydrin-positive, phosphorus-negative lipid from Paracoccus denitrificans ATCC 13543 has been isolated and purified by mild alkaline methanolysis followed by silicic acid column chromatography and preparative thin-layer chromatography. The lipid was identified as an ornithine-containing lipid. The major ester-linked fatty acid was cis vaccenic acid. Major amide-linked fatty acids were 3-OH-20:1 and 3-OH-18:0. Ornithine-containing lipid was a major lipid component of P. denitrificans. Phospholipids made up about 57% and ornithine-containing lipid about 14% of the weight of the total lipid of the organism. The ratios of lipid ornithine: lipid phosphorus were 0.23, 0.65 and 0.58 in cytoplasmic membrane, outer membrane, and an NaCl extract, which is thought to represent chiefly outer membrane, respectively. Thus ornithine-containing lipid appears to be present in larger amounts in outer membrane than cytoplasmic membrane. No substantial variations in lipid ornithine levels were noted in stationary phase versus exposnential phase organisms, organisms grown in complex medium versus organisms grown in minimal medium with and without amino acid supplements, or in organisms grown in low phosphate-containing medium.Non standard abbreviations TLC thin-layer chromatography - Tris-HCl tris(hydroxymethyl)aminomethane hydrochloride - TMS trimethylsilyl - TFA triluoroacetyl - NPPN ninhydrin-positive, phosphorus-negative - ECL equivalent chain length     

Thermoregulatory behavior of the bluespotted sunfish,Enneacanthus Gloriousus

Twenty bluespotted sunfish, Enneacanthus gloriosus, were individually tested for thermoregulatory behavior in an electronic shuttlebox. The first fishes of this genus to be tested for thermoregulatory behavior, these individuals were captured near the northern limit of their zoogeographic range, in northeastern Pennsylvania. The mean final preferendum from pooled data of all 20 fish was 28.5°C; there were no significant differences between day and night.     

The effect of manganese oxides and manganese ion on growth and siderophore production by Azotobacter vinelandii

The addition of manganese oxides to iron-limited medium promoted the formation of the pyoverdin siderophore azotobactin by Azotobacter vinelandii. When active-MnO₂ was used, there was greatly decreased iron uptake into the cells, hyperproduction of azotobactin and the abiotic, chemical destruction or adsorbtion of the catechol siderophores azotochelin and aminochelin by this strong oxidizing agent. Although the iron content of the cells was the same as iron-limited cells, the growth of cells in medium with active-MnO₂ was increased 1.5- to 2.5-fold over iron-limited controls. This growth promotion was not caused by iron contaminating the oxide or by manganese solubilized from the oxide. Soluble 0.05–4 mm Mn²⁺ inhibited the growth of iron-limited cells and had a minimal effect on iron uptake, but caused hyperproduction of azotobactin. This later effect was caused by the inhibition of soluble ferric reductase, in a manner identical to that previously observed for Zn²⁺. These results suggest that active-MnO₂ may interfere with a surface-localized iron uptake site, possibly another ferric reductase. The reason for the growth promotion by active-MnO₂ remains unknown, but is most likely related to decreased oxygen toxicity.     

Ectothiorhodospira vacuolata sp. nov., a new phototrophic bacterium from soda lakes

A new phototrophic bacterium was isolated from Jordanian and Kenyan alkaline salt lakes. Cells are rod shaped, 1.5 m wide and 2–4 m long, and motile by polar flagella. They divide by binary fission, and possess photosynthetic membranes as lamellar stacks similar to those in the other species of the genus Ectothiorhodospira and the brown colored Rhodospirillum species. The presence of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series is indicated by the absorption spectra of living cells. Under certain growth conditions the cells form gas vacuoles, may become immotile and float to the top of the culture medium. Sulfide and thiosulfate are used as photosynthetic electron donors. During the oxidation of sulfide to sulfate, elemental sulfur is formed, which is accumulated outside the cells. The organisms are strictly anaerobic, do not require vitamins, are moderately halophilic and need alkaline pH-values for growth. The new species Ectothiorhodospira vacuolata is proposed.