Impacts of agricultural practices on pyrethroid resistance in Culex pipiens pipiens, an important vector of human diseases, from Tunisia.

Agricultural pesticides may play a profound role in selection of resistance in field populations of mosquito vectors. The aim of the present study was to examine the relationship between agricultural pesticide use and development of resistance to insecticides in Culex pipiens pipiens from Tunisia. Entomological surveys were conducted in three various districts from Tunisia differ in insect control in agriculture and in public health. A reference locality without any chemical activities was used to do different comparisons. Our results revealed that the level of permethrin resistance ranged from 40.9 to 7438. Practically no susceptible populations were found and resistance to permethrin was important, but significantly higher in site submitted to both agricultural and public health applications. However, resistance ratio has been decreased 7000 folds in site not submitted to agricultural pests. These observations expressed an important influence of agricultural applications on permethrin resistance and need an urgent coordination between the integrated vector control program and the Ministry of Agriculture to reduce the development of resistance in populations. The recorded resistance was slightly associated with DDT suggest the involvement of their common mechanism (target site). Synergist's tests indicated that different enzymes played an important role in the detoxification of this insecticide.

Impacts of agricultural practices on pyrethroid resistance in Culex pipiens pipiens, an important vector of human diseases, from Tunisia

@#Agricultural pesticides may play a profound role in selection of resistance in field populations of mosquito vectors. The aim of the present study was to examine the relationship between agricultural pesticide use and development of resistance to insecticides in Culex pipiens pipiens from Tunisia. Entomological surveys were conducted in three various districts from Tunisia differ in insect control in agriculture and in public health. A reference locality without any chemical activities was used to do different comparisons. Our results revealed that the level of permethrin resistance ranged from 40.9 to 7438. Practically no susceptible populations were found and resistance to permethrin was important, but significantly higher in site submitted to both agricultural and public health applications. However, resistance ratio has been decreased 7000 folds in site not submitted to agricultural pests. These observations expressed an important influence of agricultural applications on permethrin resistance and need an urgent coordination between the integrated vector control program and the Ministry of Agriculture to reduce the development of resistance in populations. The recorded resistance was slightly associated with DDT suggest the involvement of their common mechanism (target site). Synergist’s tests indicated that different enzymes played an important role in the detoxification of this insecticide.

Characterization of resistance to pirimiphos-methyl (an organophosphate insecticide) in Culex pipiens pipiens (Diptera: Culicidae) from Northern and Southern Tunisia.

Despite the public health importance of Culex pipiens pipiens, their resistance to pirimiphos-methyl insecticides has not been explored enough. Late third and early fourth larvae of Culex pipiens pipiens were collected from three localities between 2003 and 2005 in Northern and Southern Tunisia. All bioassays were carried out using pirimiphosmethyl and propoxur insecticides. Populations of Culex pipiens pipiens were susceptible, moderate and resistant to pirimiphos-methyl insecticide. Resistance to this compound ranged from 2.62 in sample # 2 to 19.9 in sample # 1. The moderate resistance (5.25) was recorded in sample # 3. Synergist's tests showed that the resistance to pirimiphos-methyl was not affected by detoxification enzymes. However, biochemical assays showed the involvement of both metabolic (esterases) and target site (insensitive acetylcholinesterase) resistance mechanisms. The highest frequencies of the resistant phenotypes ([RS] and [RR]) (<0.74) were detected in the most resistant samples (#1). Four esterases enzymes including C1 encoded by the Est-1 locus and three esterases encoded by the Ester super locus: A2-B2, A4-B4 (or A5-B5, which has the same electrophoretic mobility) and B12 were detected. The highest (0.61) and the lowest (0.22) frequencies of these esterases were recorded in samples # 1 (Sidi Hcine) and # 2 (El Fahs) which recorded the highest and the lowest level of resistance, respectively. Monitoring of insecticide resistance should be evaluated regularly for management of vector control.

Multiple resistance mechanisms associated with low pirimifos-methyl resistance in Culex pipiens pipiens in three populations of Tunisia.

The aim of this study was to evaluate the resistance status of Culex pipiens pipiens to pirimiphos-methyl insecticide. Three field populations of mosquitoes were collected from Tunisia and analyzed in laboratory. The samples studied showed low level of resistance not exceeding 5-folds. The low resistance recorded is particularly interesting, because it leaves a range of tools useable by vector control services. Both metabolic and target-site resistance mechanisms were identified. Different esterases of high activity including A2-B2, A4-B4 (and/or A5-B5) and B12 were observed in studied field samples using starch electrophoresis although opposite results were found using synergists tests on samples # 1 and 3. The polymorphism of AChE1 (Acetylcholinesterase) was analyzed and three phenotypes were detected: susceptible (ACHE1S, phenotype [SS]), resistant (ACHE1R, phenotype [RR]), and heterozygous (phenotype [RS]) of ACHE1. The resistance of Culex pipiens pipiens to pirimiphos-methyl remains low although the occurrences of multiple resistance mechanisms are able to confer high resistance levels to organophosphate insecticides. Therefore, continuous monitoring of resistance is fundamental for rational use of insecticides and mosquito control programs.

Multiple resistance mechanisms associated with low pirimifos-methyl resistance in Culex pipiens pipiens in three populations of Tunisia

@#The aim of this study was to evaluate the resistance status of Culex pipiens pipiens to pirimiphos-methyl insecticide. Three field populations of mosquitoes were collected from Tunisia and analyzed in laboratory. The samples studied showed low level of resistance not exceeding 5-folds. The low resistance recorded is particularly interesting, because it leaves a range of tools useable by vector control services. Both metabolic and target-site resistance mechanisms were identified. Different esterases of high activity including A2-B2, A4-B4 (and/or A5-B5) and B12 were observed in studied field samples using starch electrophoresis although opposite results were found using synergists tests on samples # 1 and 3. The polymorphism of AChE1 (Acetylcholinesterase) was analyzed and three phenotypes were detected: susceptible (ACHE1S, phenotype [SS]), resistant (ACHE1R, phenotype [RR]), and heterozygous (phenotype [RS]) of ACHE1. The resistance of Culex pipiens pipiens to pirimiphos-methyl remains low although the occurrences of multiple resistance mechanisms are able to confer high resistance levels to organophosphate insecticides. Therefore, continuous monitoring of resistance is fundamental for rational use of insecticides and mosquito control programs.

Characterization of resistance to pirimiphos-methyl (an organophosphate insecticide) in Culex pipiens pipiens (Diptera: Culicidae) from Northern and Southern Tunisia

@#Despite the public health importance of Culex pipiens pipiens, their resistance to pirimiphos-methyl insecticides has not been explored enough. Late third and early fourth larvae of Culex pipiens pipiens were collected from three localities between 2003 and 2005 in Northern and Southern Tunisia. All bioassays were carried out using pirimiphosmethyl and propoxur insecticides. Populations of Culex pipiens pipiens were susceptible, moderate and resistant to pirimiphos-methyl insecticide. Resistance to this compound ranged from 2.62 in sample # 2 to 19.9 in sample # 1. The moderate resistance (5.25) was recorded in sample # 3. Synergist’s tests showed that the resistance to pirimiphos-methyl was not affected by detoxification enzymes. However, biochemical assays showed the involvement of both metabolic (esterases) and target site (insensitive acetylcholinesterase) resistance mechanisms. The highest frequencies of the resistant phenotypes ([RS] and [RR]) (>0.74) were detected in the most resistant samples (#1). Four esterases enzymes including C1 encoded by the Est-1 locus and three esterases encoded by the Ester super locus: A2-B2, A4-B4 (or A5-B5, which has the same electrophoretic mobility) and B12 were detected. The highest (0.61) and the lowest (0.22) frequencies of these esterases were recorded in samples # 1 (Sidi Hcine) and # 2 (El Fahs) which recorded the highest and the lowest level of resistance, respectively. Monitoring of insecticide resistance should be evaluated regularly for management of vector control.

Mesophilic biogas production from fruit and vegetable waste in a tubular digester.

A semi-continuously mixed mesophilic tubular anaerobic digester was tested for the conversion of fruit and vegetable waste (FVW) into biogas. The effect of hydraulic retention time (HRT) and the feed concentration on the extent of the degradation of the waste was examined. Varying the HRT between 12 and 20 days had no effect on the fermentation stability and pH remained between 6.8 and 7.6, but an inhibition of methanogenic bacteria was observed at HRT below 12 days. The overall performance of the reactor was depressed by changing the feed concentration from 8% to 10% TS (dry weight). By applying a feed concentration of 6% and HRT of 20 days in the tubular digester, 75% conversion efficiency of FVW into biogas with a methane content of 64% was achieved.

Influence of prolonged fasting and thyroid hormone on the alpha 2-adrenergic response in isolated epididymal adipocytes of Wistar rats.

Fasting and thyroid hormone have been reported to modulate the beta-adrenergic pathway of lipolysis in rat, but their effects on the alpha 2-adrenergic response are not well known. The purpose of the present study was to investigate this point. Male Wistar rats, 3 weeks old, were thyroidectomized surgically, kept for 1 month at 25 degrees C and then fasted or not fasted for 3 days with or without daily intraperitoneal injection of 3,5,3'-tri-iodo-L-thyronine (T3; 4.6 nmol/100 g body weight). Age-matched, sham-operated, fed and fasted euthyroid rats were used as controls. The experiments were carried out using isolated epididymal adipocytes. The alpha 2-adrenergic agonist UK 14304 (UK) inhibited the stimulated lipolysis more in fed than in fasted euthyroid rats whereas it had no effect in hypothyroid or T3-treated hypothyroid rats. The alpha 2-adrenergic antagonist idazoxan reversed the antilipolytic effect of UK more in fasted than in fed euthyroid rats. The alpha 2-adrenergic antagonist RX 821002 (RX) did so, but at lower concentrations than those of idazoxan. Idazoxan slightly increased the glycerol release in hypothyroid and especially T3-treated hypothyroid rats. RX had practically no effect on the production of glycerol in these animals. The findings suggest that (a) fasting and probably hypothyroidism decrease the alpha 2-adrenergic response in adipocytes from rats, (b) T3 treatment of hypothyroid rats has no effect on the alpha 2 response, and (c) thyroid hormone does not directly modulate the alpha 2-adrenergic response in rat adipocytes.

Influence of prolonged fasting on thyroid hormone modulation of lipolysis in isolated epididymal adipocytes of Wistar rats.

Male Wistar rats, 3 weeks old, were thyroidectomized surgically, kept for 1 month at 25 degrees C and then fasted for 3 days, with or without daily intraperitoneal injection of 3,5,3'-triiodo-L-thyronine (4.6 nmol T3/100 g body weight). Age-matched fed euthyroid rats were used as controls. All the experiments were carried out using isolated epididymal adipocytes. Basal lipolysis was higher during fasting in euthyroid or T3-treated adipocytes than in hypothyroid adipocytes. Adipocytes of fed hypothyroid rats were quite unresponsive to theophylline alone or combined with adrenaline or isoproterenol, whereas lipolysis was stimulated by these drugs in euthyroid or T3-treated adipocytes. Such a stimulated lipolysis was increased partially by fasting in hypothyroid adipocytes and was restored to a euthyroid level in T3-treated adipocytes. Lipolysis was more stimulated by adenosine deaminase in fasted euthyroid adipocytes than in fed ones. Hypothyroid and T3-treated adipocytes were unresponsive to adenosine deaminase except in fasted T3-treated rats. In these adipocytes, lipolysis was activated by the combination of adenosine deaminase plus theophylline. Finally, lipolysis was inhibited strongly in hypothyroidism while it was activated weakly by fasting. Lipolysis was inhibited slightly in fasted hypothyroid rats and thyroid hormone restored lipolysis. The findings are discussed in terms of the dual regulation of lipolysis by fasting and thyroid hormones.

Changes in thyroid hormone and thyrotrophin in the serum and thyroid glands of developing genetically obese male and female Zucker rats.

In a first experiment, serum thyroxine (T4), 3,5,3'-triiodothyronine (T3) and thyrotrophin (TSH) concentrations as well as thyroid gland T4 and T3 contents were measured in developing lean and obese Zucker male and female rats of 4-16 weeks of age. The rats were bred in our laboratory and always treated in sex-matched pairs of one lean and one obese rat from the same litter. Serum T4 was not different in any phenotype/sex group at 4 weeks. In male rats, it became progressively lower (27 and 37% at 12 and 16 weeks respectively) in obese than in lean rats. In females, similar levels of serum T4 were maintained in both obese and lean developing rats. Serum T3 was similar in obese and lean male 4-week-old rats whereas it was lower (28%) in obese than in lean females. It became progressively lower (39 and 49% at 12 and 16 weeks respectively) in obese than in lean developing male rats. In females, lower levels of serum T3 were maintained (25 and 43% at 12 and 16 weeks respectively) in obese than in lean rats. Serum TSH was not different in any phenotype/sex group at 4 weeks. It rose in both obese and lean male rats with age, but became progressively lower (33 and 23% at 12 and 16 weeks respectively) in obese compared with lean rats. In females, similar levels of serum TSH were maintained in both obese and lean developing rats. Thyroid gland weight was not different in any phenotype/sex group at 4 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Control of oxidative metabolism in volume-overloaded rat hearts: effects of different lipid substrates.

The relationship between intracellular energy parameters and myocardial O2 consumption (VO2) was studied in control and volume-overloaded hearts perfused with different lipid substrates and over a range of left ventricular work loads. In control hearts, a unique linear relationship between log of cytosolic [ATP]/[ADPf].[Pi] (where [ADPf] is concentration of free ADP) and myocardial VO2 was observed between low and high work loads for both fatty acids studied. In volume-overloaded hearts perfused in the presence of exogenous palmitate, the slope of the relationship between log [ATP]/[ADPf].[Pi] and myocardial VO2 was considerably depressed. It would seem that, under these conditions, much of the thermodynamic control of respiratory chain function has been lost. When myocardial VO2 was expressed as a function of cytosolic ADPf, the cytosolic ADPf was not regulatory. This may be related to a substrate limitation of the respiratory chain, as suggested by an excessive oxidation of pyridine nucleotides. When octanoate, instead of palmitate, was used, most of the above limitation of the respiration disappeared. With this substrate, the reduction of mitochondrial pyridine nucleotides in volume-overloaded hearts was similar to that in controls, and the linear relationship between log [ATP]/[ADPf].[Pi] and myocardial VO2 reappeared over the range of work loads studied. The above failure of cytosolic phosphate potential and ADPf to drive respiration when mitochondrial NADH is low fits well with the integrated model of kinetic regulation, as proposed by recent nuclear magnetic resonance studies. our results also indicate that, even at high respiratory rates, free-energy change of ATP synthesis of volume-overloaded hearts can be protected by use of an appropriate substrate. This, in turn, prevents contractile failure.

[Prolonged fasting on the lipolytic activity of isolated adipocytes of the rat epididymis]. / Effet du jeûne prolongé sur l'activité lipolytique de l'adipocyte isolé de l'épididyme de rat.

Male Wistar rats, 6-8 week old, were fasted for 72 hours. The in vitro lipolytic activity of epididymal adipocytes was measured in the presence of adrenalin (a alpha and beta adrenergic agonist), isoprenaline (a pure beta agonist), theophylline (a phosphodiesterase inhibitor) or UK 14304 (a alpha 2 adrenoceptor agonist) associated with adenosine deaminase. The basal lipolytic activity, expressed per 100 mg lipids, was higher in fasted adipocytes than in fed ones. Its stimulation by adrenalin or isoproterenol was decreased by fast. The effects of these drugs were more potentiated by theophylline in fasted adipocytes than in fed ones. The UK 14304 inhibition of adenosine deaminase-stimulated lipolysis was about 20% in fasted adipocytes and 50% in fed adipocytes. The in vitro resistance of fasted adipocytes to the lipolytic effect of adrenalin or isoproterenol may be related to the hypothyroid status of fasted rats.