A mosquito predator survey in Townsville, Australia, and an assessment of Diplonychus sp. and Anisops sp. predatorial capacity against Culex annulirostris mosquito immatures.

A twelve-month survey for mosquito predators was conducted in Townsville, Queensland, Australia, which is located in the arid tropics. The survey revealed the presence of five predaceous insects but only Anisops sp. (backswimmers) and Diplonychus sp. were common. Predatorial capacity and factors influencing this capacity were then assessed for adult Anisops sp. and adult and nymph stages of Diplonychus sp. against Culex annulirostris mosquito immatures under laboratory conditions. Predatorial capacity bioassays showed that adult Diplonychus sp. preyed upon both larval and pupal stages of Cx. annulirostris quite successfully. Nymphs of Diplonychus sp. proved to be more successful with smaller prey immatures, and Anisops sp adults did not prey successfully on any prey pupae. Increasing the foraging area and introducing aquatic vegetation significantly reduced the predatorial capacity of Diplonychus sp. nymphs, while only vegetation and not foraging area had a significant effect on adult Diplonychus sp. predation capacity. Overall, adult Diplonychus sp. proved to be a more efficient predator than Anisops sp., and field trials are now recommended to further assess the potential of Diplonychus sp. as a biocontrol agent.

Efficacy of eight larvicidal botanical extracts from Khaya senegalensis and Daucus carota against Culex annulirostris.

The failure to discover a significant new class of insecticides has led many researchers back to biodiscovery studies in the search for new and economically viable alternatives. After a preliminary screening of botanical extracts using descending series of concentrations (1,000, 500, 100, 50, and 5 mg/liter), 8 extracts from 2 potential botanical agents, Khaya senegalensis (Desrousseaux) and Daucus carota L., were tested against 4th instars of Culex annulirostris (Skuse) following the standard World Health Organization insecticide susceptibility methodology. The median lethal concentration (LC50) values for K. senegalensis against Cx. annulirostris using acetone, ethanol, hexane, and methanol extracts were 20.12, 5.1, 5.08, and 7.62 mg/liter, respectively. The LC50 values for D. carota against Cx. annulirostris using acetone, ethanol, hexane, and methanol extracts were 236.00, 36.59, 77.19, and 241.8 mg/liter, respectively. Extracts from K. senegalensis were more potent than those from D. carota against Cx. annulirostris and hexane and ethanol were the best solvents to extract essential oils from both plant species, respectively. In potency, K. senegalensis was similar to azadirachtin, but fractionation and compound isolation of the hexane extract in particular may reveal a potent phytochemical that could be compared to synthetic mosquitocides.

A review of botanical phytochemicals with mosquitocidal potential.

Identification of novel effective mosquitocidal compounds is essential to combat increasing resistance rates, concern for the environment and food safety, the unacceptability of many organophosphates and organochlorines and the high cost of synthetic pyrethroids. An increasing number of researchers are reconsidering botanicals containing active phytochemicals in their efforts to address some of these problems. To be highly competitive and effective, the ideal phytochemical should possess a combination of toxic effects and residual capacity. Acute toxicity is required at doses comparable to some commercial synthetic insecticides while chronic or sub-chronic toxicity is required to produce growth inhibition, developmental toxicity and generational effects. In this article, we review the current state of knowledge on larvicidal plant species, extraction processes, growth and reproduction inhibiting phytochemicals, botanical ovicides, synergistic, additive and antagonistic joint action effects of mixtures, residual capacity, effects on non-target organisms, resistance, screening methodologies, and discuss promising advances made in phytochemical research.

Synergistic efficacy of botanical blends with and without synthetic insecticides against Aedes aegypti and Culex annulirostris mosquitoes.

Increasing insecticide resistance requires strategies to prolong the use of highly effective vector control compounds. The use of combinations of insecticides with other insecticides and phytochemicals is one such strategy that is suitable for mosquito control. In bioassays with Aedes aegypti and Culex annulirostris mosquitoes, binary mixtures of phytochemicals with or without synthetic insecticides produced promising results when each was applied at a LC25 dose. All mixtures resulted in 100% mortality against Cx. annulirostris larvae within 24 h rather than the expected mortality of 50%. All mixtures acted synergistically against Ae. aegypti larvae within the first 24 h except for one mixture that showed an additive effect. We conclude that mixtures are more effective than insecticides or phytochemicals alone and that they enable a reduced dose to be applied for vector control potentially leading to improved resistance management and reduced costs.

Effects of sub-lethal concentrations of synthetic insecticides and Callitris glaucophylla extracts on the development of Aedes aegypti.

Synthetic and botanical insecticides can have a profound effect on the developmental period, growth, adult emergence, fecundity, fertility, and egg hatch, resulting in effective control at sub-lethal concentrations. This paper investigated sub-lethal concentrations of fenitrothion, lambda-cyhalothrin, and Callitris glaucophylla Joy Thomps. & L.P. Johnson (Cupressaceae) extract to characterize their effects on the development of Aedes aegypti L. (Diptera: Culicidae) mosquito larvae. The LC25, LC50, and LC75 (four replicates) were used for each synthetic insecticide and the LC25 and LC75 (four replicates) were used for C. glaucophylla. Observations of larval mortality, duration of larval stage, pupal mortality, duration of pupal stage, adult emergence, sex ratio, and malformations were recorded over 14 days. A dose-response effect was observed for all insecticides. Although C. glaucophylla extract doses were higher than synthetic insecticide doses, the LC75 treatment outperformed synthetics by completely prohibiting adult emergence. Consequently, this botanical is recommended for field application either in combination with synthetic or natural insecticides or alone.