Susceptibility status of Anopheles gambiae s.l. (Diptera: Culicidae) from cabbage growing areas associated with pyrethroid and organophosphate use in Accra, Ghana

Resistance in malaria vectors is likely to be caused by the massive use of insecticides in agriculture. Anopheles gambiae s.l. collected from breeding grounds in two cabbage growing areas within Accra were assessed for levels of resistance to 0.75% permethrin, 0.05% deltamethrin, 5% malathion and 4% DDT using standard WHO susceptibility test kits. Pyrethroid and organophosphate residue levels in soil and run-off water from these cabbage farms were determined and possible association between resistance and residue levels were established. Compared to thesusceptible ‘Kisumu’ strain, both Korle-Bu and Airport populations were highly resistant to DDT and gave resistance levels which were over nine-fold for permethrin and over 2.5-fold for deltamethrin. Both wild and susceptible populations showed full susceptibility to malathion. The S and M forms of A. gambiae s.s. were found to occur in sympatry in the two study sites with a higher frequency of S form in the Airport area. Toxicity testing of extracts of soil and run-off water from these cabbage farms, using brine shrimp lethality tests, showed high level of toxicity, indicativeof the presence of residues of insecticides. Differential fractionation of these extracts using solid phase extractor (SPE) suggests that the bulk of residues in these extracts may be pyrethroids and organophosphates. No correlation was observed between either residue levels or residual bioactivity in soil and run-off water, and resistance levels in A.gambiae s.l. populations, collected from breeding grounds within the farms under investigation. It is proposed that resistance in A. gambiae larvae in these breeding sites contaminated with agricultural insecticides may have occurred over time due to continuous exposure to sub-lethal doses

Resistance of diamondback moth to insecticides in selected cabbage farms in southern Ghana

Resistance of diamondback moth (DBM), Plutella xylostella (L.) to insecticides applied for its control on cabbage was evaluated. DBM populations were tested for susceptibility to three pyrethroids (delatamethrin, lambdacyhalothrin, cypermethrin) and an organophosphate (chlorpyrifos-methyl) insecticide using larvaeimmersion dose-response technique. Non-specific carboxylesterase activity was used as a measure of DBM resistance. Partial characterization of carboxylesterase by zymogram studies was also undertaken usingpolyacrylamide gel electrophoresis (PAGE). Susceptibility studies revealed that DBM was resistant to the four insecticides assayed. DBM was least susceptible to chlorpyrifos-methyl, but most susceptible to deltamethrin.Esterase zymogram studies revealed between 2 to 7 bands, each with different characteristics. Higher frequency of the slow-moving esterases associated with high resistance was recorded in Mampong DBMpopulation than the Accra suburbs. This finding confirmed results for carboxylesterase activity. Deltamethrin and cypermethrin demonstrated high negative correlation between fold resistance and carboxylesterase activity for â-isozyme. Chlorpyrifos-methyl, on the other hand showed positive correlation between fold resistance and á-carboxylesterase activity. The high carboxylesterase activities recorded for Mampong DBM, however, did not correlate with results of susceptibility studies. It is suggested that farmers should adopt an integrated approach using the IPM principles coupled with judicious use of biopesticides such as Bacillus thuringiensis.© 2010 International Formulae Group. All rights reserved

Modulation of Penile Erection in Rabbits by Mondia Whitei: Possible Mechanism of Action

Mondia whitei root was evaluated to validate its anecdotal use and determine its possible mode of action in the management of erectile dysfunction. Rabbits were administered with daily oral doses of 100–400 mg kg−1 crude ethanolic extract of M. whitei and sildenafil (50 mg kg−1) as positive control for 6 weeks. Cavernosal tissue NOS activity and levels of NO and cGMP, and NOS and PDE protein expressions were investigated. The effect of the crude extract, chloroform and petroleum ether fractions in vitro on cavernosal tissue NOS activity and levels of NO and cGMP at 0.01 and 0.10 mg g−1 tissue were also investigated. Results indicate that the crude extract increased NOS activity by 7% at 200 mg kg−1 with corresponding increases in NO (88%) and cGMP (480%) levels. No significant changes in these measurements were observed with the 100 and 400 mg kg−1 doses whilst sildenafil slightly reduced them (15.9–37.5%). NOS and PDE protein expressions in test animals were not different from controls. Pre-incubation of cavernosal tissue in vitro with the crude extract of M. whitei and its chloroform fraction markedly increased NOS activity (26–132%) and levels of NO (25%) and cGMP (50–400%) at 0.01 mg g−1 tissue but these were reduced to near control levels when their concentrations were increased to 0.10 mg g−1 tissue whilst the petroleum ether fraction had no effect. These findings suggest that M. whitei may influence erectile function through activation/stimulation of NOS with corresponding increases in tissue NO and cGMP levels and that certain chemical constituents present in the chloroform fraction may be responsible for biological activity