[Susceptibility status of Anopheles gambiae s.s. and An. coluzzii to Organophosphates and Carbamates in the Agricultural Exploitation Zones of oil Palm at Mouila, Gabon]

This study was conducted during the rainy season of 2017 in the agricultural areas at Mouila, with the aim to assess the determination of susceptibility of Anopheles gambiae complex to insecticides and the detection of Ace 1^R mutation. Mosquito larvae were collected by using the dipping method and nursed to adult stage. The susceptibility of adult Anopheles gambiae s.l. populations to organophosphates and carbamates was assessed using the standard WHO susceptibility test protocol. The tested mosquitoes species were identified by PCR. These tested mosquitoes were used to search for the Ace 1^R mutation. The insecticides used were pirimiphos-methyl 0.25% and 1.25%, fenitrothion 1%, malathion 5%, propoxur 0.1%, bendiocarb 0.1%, 0.5% and 1%. In the prospected areas, An. gambiae s.l. included An. gambiae s.s. and An. coluzzii sympatric in their larval habitats. However, An. gambiae s.s. was predominant in all studied areas (99.1%) comparatively to An. coluzzii Moreover, the susceptibility tests of Anopheles to organophosphates and carbamates revealed mortality rates of 100% regardless of the origin of the mosquitoes. PCR diagnosis of Ace 1^R mutation showed that none tested mosquito (An. gambiae s.s. and An. coluzzii) from prospected areas harbored the Ace 1^R gene in all prospected areas. The lack of Ace 1^R mutation in An. gambiae s.l. reveals the current effectiveness of organophosphates and carbamates for the control of these mosquitoes. Bboth these classes of insecticides could be used for the anopheline populations control in the agricultural spaces at Mouila.

Inventory of potential vectors of trypanosoma and infection rate of the Tsetse fly in the National Park of Ivindo, Gabon

BACKGROUND

Trypanosoma's vectors distribution is poorly investigated in Gabon, where Trypanosomiasis historical foci exist. Thus, an active detection of Trypanosoma sp transmission needs to be assessed.

OBJECTIVES

The present study aims to identify potential vectors of Trypanosoma sp and to evaluate the infection rate of the Tsetse fly in an area of Gabon.

METHODS

An entomological survey was conducted in the National Park of Ivindo in May 2012 using Vavoua traps. All captured insects were identified. Tsetse were dissected and organs were microscopically observed to detect the presence of Trypanosoma sp.

RESULTS

247 biting flies known as vectors of Trypanosomiasis were caught including 189 tsetse flies, 32 Tabanid and 26 Stomoxys. Tsetse flies had the highest bulk densities per trap per day (ADT = 3 tsetse / trap / day), while the lowest density was found among Stomoxys (ADT= 0.41 Stomoxys / trap / day). The infection rate of flies was 6.3%. Infectious organs were midguts and to a lesser extent salivary glands and proboscis.

CONCLUSION

The presence of Tsetse infected by Trypanosoma highlights an existing risk of trypanosomiasis infection in the National Park of Ivindo.

Spatio-temporal variation of biting flies, Stomoxys spp. (Diptera: Muscidae), along a man-made disturbance gradient, from primary forest to the city of Makokou (North-East, Gabon)

Understanding the pattern of abundance of vector populations is important to control the potential of transmission of associated pathogens. The pattern of abundance of Stomoxys Geoffroy, an ubiquitous blood-sucking fly, is poorly known in tropical Africa. In this study, we investigated the spatio-temporal pattern of abundance of the Stomoxys genus along a gradient of man-made disturbance in north-eastern Gabon. Three sites (one in primary forest, one in secondary forest and one in a man-made environment) were monitored during 13 months using Vavoua traps. Seven species and subspecies were found to live in sympatry, but with distinct patterns of abundance with respect to space and time. The most abundant species was Stomoxys transvittatus Villeneuve, whereas the rarest species was S. xanthomelas Roubaud. Stomoxys calcitrans Linné was preferentially found in man-made environments, whereas S. xanthomelas was preferentially found in primary forest. Stomoxys abundance was the greatest in secondary forest, then in man-made environments and finally in primary forest. A seasonal variation in Stomoxys abundance was also found. In conclusion, forest degradation and deforestation are likely both to favour the concentration of populations of Stomoxys, and to change the specific composition of the Stomoxys community.

Effect of Tephrosia vogelii and Justicia extensa on Tilapia nilotica in vivo

According to our and other ethnobotanic studies (Walker, R., 1951. Une Nouvelle Légumineuse du Gabon servant à narcotiser le poisson. Rev. Bot. Appl. 31, 327; Walker, R., Sillans, R., 1961. Les plantes utiles du Gabon. Encyclopédie Biologique. P. Chevalier, Paris; Halle, N., 1970. Flore du Gabon 17, Famille des Rubiacées. Museum National d'Histoire Naturelle, Paris; Mounzeo, H., et al., 1997. Quelques plantes utilisées comme poisons de pêches chez les Punu du Gabon. Le Flamboyant 44. Décembre, Bulletin de Liaison des membres du réseau 'Arbres Tropicaux'), Tephrosia vogelii and Justicia extensa are two plants whose leaves are particularly used for the catching of fish in Gabonese rivers. The leaf extracts of those plants have been tested on Tilapia nilotica in order to observe their toxicity. At a given dose, the small fish are the first to be poisoned. This toxicity is more important for J. extensa and increased in a dose-dependent manner. After boiling for 90 min, those leaf extracts and rotenone (10(-6) M) taken as a control retain their toxicity at high dose (625 mg/l), although the latency period is higher. With the same temperature condition, at weak doses (37.5 and 62.5 mg/l), T. vogelii loses its toxicity, whereas J. extensa preserves it at 62.5 mg/l. As shown in our results, the fact that the extracts preserve their toxicity at high dose after boiling requires particular attention be given to the doses used for fishing and to the type of plants used.

Stimulation of sugar exit from leaf tissues ofVicia faba L

After removal of the lower epidermis, leaf discs ofVicia faba L. were loaded with either [(14)C]sucrose or [(3)H]3-O-methylglucose (3-O-MeG). The exit of preloaded sucrose was strongly stimulated when sucrose was present in the bathing medium, and the exit of 3-O-MeG was also markedly increased in the presence of 3-O-MeG. This specific stimulation exhibited single saturation dependence on the external concentration of sugar (K m=9 mM for sucrose, 5 mM for 3-O-MeG), and was sensitive to low temperature, uncouplers and thiol reagents. Sucrose exit was never affected by 3-O-MeG in the bathing medium. Sucrose did not affect the exit of 3-O-MeG in fresh discs, but promoted this exit in discs previously aged for 12 h, indicating partial external hydrolysis of sucrose in the latter tissues. Ageing also dramatically increased the exit of 3-O-MeG induced by 3-O-MeG but had no effect on the exit of sucrose induced by sucrose. The ability of 53 compounds (pentoses, hexoses, hexose-phosphates, polyols, di- and trisaccharides, phenyl- and nitrophenyl-derivatives, sweeteners) to interact with the sucrose carrier and with the hexose carrier was tested. Sucrose, maltose, α-phenylglucoside andp-nitrophenyl-α-glucoside interacted with the sucrose carrier.D-glucose,D-xylose,D-fucose,D-galactose,D-mannose, 3-O-MeG and 2-deoxyglucose interacted with the hexose carrier.

Selective Solubilization of Membrane Proteins Differentially Labeled by p-Chloromercuribenzenesulfonic Acid in the Presence of Sucrose

Broadbean (Vicia faba L.) leaf discs have been incubated with the slowly permeant thiol reagent [(203)Hg]-para-chloromercuribenzenesulfonic acid (PCMBS) in the presence or in the absence of sucrose, and the release of PCMBS-labeled proteins has been monitored in media containing various concentrations of urea, ethyleneglycol-bis-(beta-aminoethyl ether)-N, N, N', N'-tetraacetic acid (EGTA), sodium cholate, sodium dodecyl sulfate, Triton X-100, octylglucoside or (3-[3-cholamidopropyl)-dimethylammonio] 1-propane-sulfonate) (CHAPS). The proteins differentially labeled by PCMBS in the presence of sucrose which, on the basis of previous results, are assumed to include the sucrose carrier, were preferentially solubilized by 1% CHAPS, 1% octylglucoside, or 1% Triton X-100. Other PCMBS-labeled proteins (;background' proteins) could be partially removed by EGTA, urea, or 0.1% cholate. Sequential treatment by 10 mm EGTA and 1% CHAPS was found to give a fraction highly enriched in the differentially labeled proteins. Analysis of the specific activity of microsomal pellets suggests that the results obtained with leaf discs give a good account of what is occurring at the plasma membrane level. These data, which suggest that the proteins differentially labeled by PCMBS in the presence of sucrose are intrinsic membrane proteins, can be used to solubilize these proteins from microsomal fractions.

The Effect of Sugars on the Binding of [Hg]-p-Chloromercuribenzenesulfonic Acid to Leaf Tissues

Replacement of mannitol with sucrose decreases the binding of [(203)Hg]-p-chloromercuribenzenesulphonic acid (PCMBS) to Vicia faba leaf discs without epidermis. This decrease is optimal for 20 minutes on incubation, is concentration-dependent, and is also found with maltose and raffinose. In parallel experiments, the addition of sucrose, maltose, and raffinose during PCMBS pretreatment was shown to increase subsequent uptake of [U-(14)C]sucrose. In contrast, d- or l-glucose, 3-O-methylglucose, galactose, fructose, palatinose, turanose, or melibiose had no effect either on PCMBS binding or on [(14)C]sucrose uptake. The sucrose-induced decrease of PCMBS binding is retained after a cold and ionic shock. Measurements of specific activities of membrane fractions prepared from tissues incubated in labeled PCMBS show that the decrease concerns the 120,000 gravity pellet, but that very mild procedures must be chosen to prevent redistribution of label in the supernatant. Altogether, the data provide new support to the hypothesis that the active site of the sucrose carrier contains a group sensitive to PCMBS.

Parachloromercuribenzenesulfonic Acid : a potential tool for differential labeling of the sucrose transporter

Vicia faba leaf discs without epidermis were pretreated with parachloromercuribenzenesulfonic acid (PCMBS), rinsed and incubated on [(14)C]sucrose (1 or 40 millimolar). Those sucrose concentrations were chosen as representative of the apparent uptake system 1 (1 millimolar) and system 2 (40 millimolar) previously characterized. Pretreatment with 0.5 millimolar PCMBS for 20 minutes inhibited system 1 and system 2 by about 70%.Addition of unlabeled sucrose during PCMBS-pretreatment protected the carrier(s) from the inhibition, whereas glucose, fructose, and sucrose analogs were unable to afford protection. At 1 millimolar [(14)C]sucrose, the protection resulted in a small but consistent reduction of normal inhibition (from 63 to 45%) for sucrose concentrations of 50 millimolar and more during pretreatment. Contrarily, at 40 millimolar [(14)C]sucrose, the protection increased linearly with the sucrose concentration in the pretreatment medium, and complete prevention of inhibition was reached for 250 millimolar sucrose.The protection was not due to exchange diffusion and was located in the veins. Michaelian kinetics indicated that PCMBS and sucrose compete with each other at the active site of the carrier.Among 14 compounds tested (sugars, amino-acids, hormones, (32)P), sucrose uptake was by far the most sensitive to PCMBS. Sucrose preferentially protected its carrier(s) from inhibition. Treatment with 20 millimolar cysteine or 20 millimolar dithioerythreitol reversed inhibition by PCMBS pretreatment.