Insecticide resistance and dominance levels

Dominance has been assessed in different ways in insecticide resistance studies, based on three phenotypic traits: the insecticide concentration required to give a particular mortality (DLC), mortality at a particular insecticide dose (DML), and fitness in treated areas (DWT). We propose a general formula for estimating dominance on a scale of 0 to 1 (0 = complete recessivity and 1 = complete dominance). DLC, DML, and DWT are not directly related and their values depend on genetic background and environmental conditions. We also show that pest management strategies can have the consequence to increase DWT via the selection of dominance modifiers. Studies on resistance to Bacillus thuringiensis toxins provide the ultimate example of the complexity of the definition of the concept of dominance. Almost all studies have focused on calculation of DLC, which provides little information about the efficiency of pest management programs. For instance, one assumption of the high dose/refuge strategy is that Bacillus thuringiensis resistance must be effectively recessive (i.e., DML must be close to zero). However, DWT, rather than DML, is relevant to the resistance management strategy. Therefore, we strongly suggest that the time has come to focus on fitness dominance levels in the presence and absence of insecticide.     

Heat-shock protein 90: intrinsic peptidase activity and in vitro long-term self-processing

When tested on Suc-Leu-Leu-Val-Tyr-MCA as substrate, purified full-length hsp90 displays a low "chymotrypsin-like" peptidase activity which is activated by Ca++ and Mg++ ions. On the other hand, using long-term in vitro experiments, we demonstrate the ability of hsp90 to convert into a 73 kDa truncated product. This autocatalytic degradation proceeds from the C-terminal end of the full-length hsp90 and shifts the oligomers toward monomeric truncated forms. This corresponds to an intermolecular process as addition of exogenous 73 kDa product speeds up the maturation kinetics. The peptidase activity is enhanced in the 73 kDa product and is sensitive to peptide aldehyde inhibitors but only partially to lactone compounds. The degradation process itself presents a great degree of similarity with the peptidase activity toward either the inhibitors or the tested ions. Neither 20S proteasome nor m-calpain are responsible for the observed activities. Indeed, the self-processing is a consequence of the peptidase activity which appears to be an intrinsic property of the chaperone. The functional importance of these findings is discussed.     

Rapid Genotyping of Mice with Hemoglobinopathies and Globin Transgenes

The hematology of the laboratory mouse has beenwell characterized. Normal genetic differences at thealpha- and beta-globin gene loci serve as useful markersfor a wide variety of types of experimental studies. There are a number of naturallyoccurring or induced mutations that disrupt globinexpression and produce thalassemic phenotypes. Inaddition, much has been learned of the workings of theglobin locus control region from studies of transgenicmice, including those with mutations induced by targetedsite-specific modifications. After a new mutation ortransgene has been created, it must be maintained in living mice, and the genotypes of theoffspring must be ascertained. While it is possible todetermine genotypes by DNA analyses, such assays aretime consuming and relatively expensive. An osmoticchallenge test -- originally developed for thegenotyping of large-deletion alpha-thalassemia mutationsin mice -- has proven useful in detecting bothsevere and milder alpha- and beta-thalassemias, as wellas some transgenic genotypes in mice carrying human globin genes.Reliable genotyping can, in some cases, be completedwithin a few minutes with minimal expense.Quantification of red cell fragility for a variety ofthalassemic and transgenic mice is described here, alongwith a simplified test suitable for rapid, routinegenotyping. The osmotic challenge test is perfectlyreliable for distinguishing genotypes that causesignificantly decreased release of hemoglobin from the redcells, but it is also useful for some of the conditionsin which overall erythrocyte osmotic fragility isessentially normal.     

Selectivity of Ferric Enterobactin Binding and Cooperativity of Transport in Gram-Negative Bacteria

The ligand-gated outer membrane porin FepA serves Escherichia coli as the receptor for the siderophore ferric enterobactin. We characterized the ability of seven analogs of enterobactin to supply iron via FepA by quantitatively measuring the binding and transport of their ⁵⁹Fe complexes. The experiments refuted the idea that chirality of the iron complex affects its recognition by FepA and demonstrated the necessity of an unsubstituted catecholate coordination center for binding to the outer membrane protein. Among the compounds we tested, only ferric enantioenterobactin, the synthetic, left-handed isomer of natural enterobactin, and ferric TRENCAM, which substitutes a tertiary amine for the macrocyclic lactone ring of ferric enterobactin but maintains an unsubstituted catecholate iron complex, were recognized by FepA (K_d ≈ 20 nM). Ferric complexes of other analogs (TRENCAM-3,2-HOPO; TREN-Me-3,2-HOPO; MeMEEtTAM; MeME-Me-3,2-HOPO; K₃MECAMS; agrobactin A) with alterations to the chelating groups and different net charge on the iron center neither adsorbed to nor transported through FepA. We also compared the binding and uptake of ferric enterobactin by homologs of FepA from Bordetella bronchisepticus, Pseudomonas aeruginosa, and Salmonella typhimurium in the native organisms and as plasmid-mediated clones expressed in E. coli. All the transport proteins bound ferric enterobactin with high affinity (K_d ≤ 100 nM) and transported it at comparable rates (≥50 pmol/min/10⁹ cells) in their own particular membrane environments. However, the FepA and IroN proteins of S. typhimurium failed to efficiently function in E. coli. For E. coli, S. typhimurium, and P. aeruginosa, the rate of ferric enterobactin uptake was a sigmoidal function of its concentration, indicating a cooperative transport reaction involving multiple interacting binding sites on FepA.     

Morphological analysis of three equivocal sibling species of Deprea (Solanaceae)

Taxonomic confusion among closely related and morphologically similar Deprea species has persisted in the literature and in the identification of species. Morphological variation among three closely related, monophyletic Deprea species was studied to determine if and how they can be distinguished. Their sympatric occurrence in Venezuela afforded an opportunity to couple field study with analysis of herbarium specimens representing their entire geographic range. An analysis of 94 morphological characters resulted in five vegetative and 13 reproductive taxonomically informative traits. Canonical variates analysis clearly separated the three species using six quantitative traits. We conclude that these taxa, although quite variable and similar morphologically, are taxonomically distinct. Results of character analysis indicated that D. orinocensis is morphologically more similar to D. bitteriana than either are to D. paneroi. In D. paneroi, small, sterile anthers on fruit-bearing plants and the absence of fruits on plants possessing large, plllen-bearing anthers, suggest cryptic dioecy. Based on these data, D. granulosa is considered to be a synonym of D. orinocensis: Athenaea bitteriana, a misapplied synonym, is the correct basionym and is applicable to many specimens identified as D. granulosa. We submit a new combination, D. bitteriana (Werderm.) Sawyer & Benítez, and designate a lectotype to accommodate these findings.     

Uptake of Thallium, a Toxic Heavy-Metal, in the Cyanobacterium Synechococcus R-2 (Anacystis nidulans, S. Leopoliensis) PCC 7942

Uptake of the toxic heavy-metal, thallium, was studied in thecyanobacterium Synechococcus R-2 (PCC 7942) using clinicallyavailable ²⁰¹Tl ⁺. Thallium was found to distribute across theplasmalemma passively, and so the accumulation ratio of theion ([Tl⁺]_i/[Tl⁺]_o) could be used to calculate the apparentmembrane potential (­_i,o) of the cells (^ETI⁺_i,o = ­_i,o).The permeability of the plasmalemma to TI⁺ (^PTI⁺ 1 to 5 nms^–1)is higher than that of K⁺. Valinomycin does not increase thepermeability of TI⁺. Transient changes in the ­_i,o of cells,because of electrogenic transport of ions, could be detectedfrom its effects upon the uptake rate of TI⁺. HCO^–₃ hyperpolarizedSynechococcus cells, whereas NH⁺₄, CH₃NH⁺, and K⁺ led to depolarization.The use of TI⁺ as a reporter of ­_i,o has some inherent limitations.Tl⁺ is toxic at very low concentrations (inhibitory effectsare apparent after about 6 h at concentrations as low as 1 mmolm^–3). The rate of equilibration is slow (t_1/25 to 20 min).Equilibration of TI⁺ takes about 2 h, which limits its valueas a membrane potential probe. Large amounts of TI⁺ bind tothe surface of the cells making the method impracticable formeasuring accumulation ratios of less than about 10 (­_i,o)values smaller than about –60 mV). Cultures continuouslyexposed to Tl⁺ (10 mmol m^–3) eventually become TI⁺ resistantby actively extruding TI⁺ (µTI⁺_i,o= –3±0.2kJ mol^–1) and so thallium cannot be used as a ­_i,oprobe in such cells. (Received October 28, 1997; Accepted August 31, 1998)     

Do Solitary Bees Osmia cornuta Latr. and Osmia lignaria Cresson Use Proximal Visual Cues to Localize Their Nest?

Female Osmia repeatedly return to their nest to provision it with food and building material. The present study investigates the bees' nest localization performance by modifying visual cues in the near-vicinity of the nest. Each of several arrays of nesting holes was surrounded by four geometrical shapes. Removing some or all of the shapes reduced the proportion of direct returns but never prevented a bee from finding the appropriate array and, within that array, its own nest. The more the pattern was modified, the higher was the error score and the longer the delay, but no bee failed finally to find its nest. Shifting the pattern as well as the whole array of holes shifted homing orientation accordingly. There was no effect of the positions of the removed shapes, of contrast inversion, or of modifying the holes array. Our data are discussed in the light of the snapshot theory.     

Resistance management: the stable zone strategy

The different strategies of insecticide resistance management that have been formulated so far consist of delaying the appearance and spread of resistance genes. In this paper, we propose a strategy that can be used even if resistance genes are already present. This strategy consists of applying insecticides in an area smaller than a certain critical size, so that gene flow from the untreated area, combined with the fitness cost of the resistance genes, prevents its frequency reaching high equilibrium value. A two-locus model was analysed numerically to determine population densities at equilibrium as a function of selection coefficients (insecticide selection, fitness costs of resistance genes and dominances), gene flow and size of the treated area. This model indicates that there is an optimal size for the treated area where a minimal and stable density reach equilibrium, and where resistance genes cannot invade. This resistance management strategy seems applicable to a large variety of field situations, but eventually it may encounter obstacles due to a modifier which reduces the fitness costs of resistance genes.