Mosquito oviposition deterrents.

Mosquitoes are well-known vectors of disease and threaten the health of millions of people annually. While synthetic insecticides have been relied on to combat these diseases, insecticide resistance and environmental concerns have directed attention towards novel and more targeted mosquitocides derived from botanicals. Research on the activity of botanical derivatives has focused on mosquito larvae and adults with little attention given to their potential as oviposition deterrents against gravid female mosquitoes. This review explores the influence of chemical and biological factors on deterrence and examines issues relating to environmental persistence and non-target effects. With very few discoveries of new insecticide pathways, the answer to effective mosquito control may well reside within other ancient plant-based organisms that have co-resided and evolved with this ubiquitous pest.

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 botanical extracts from Callitris glaucophylla, against Aedes aegypti and Culex annulirostris mosquitoes

Using standard WHO methodology, this study investigated the susceptibility of 4(th) instar Aedes aegypti (L) and Culex annulirostris (Skuse) larvae to three extracts from Callitris glaucophylla (J. Thompson & L. Johnson) (1: steam distillation extract, 2: liquefied refrigerant gas extract, and 3: methanol reflux extract), lambda-cyhalothrin (a synthetic pyrethroid insecticide) and fenitrothion (an organophosphorous insecticide). Cx. annulirostris was significantly more susceptible than Ae. aegypti to all tested chemicals except lambda-cyhalothrin. Responses to the three C. glaucophylla extracts were exceptional for a botanical compound: Cx. annulirostris (LC(50) = 0.23, 9.53 and 38.95 mg/L) and Ae. aegypti (LC(50) = 0.69, 5.21 and 306.43 mg/L). Both Cx. annulirostris and Ae. aegypti larvae were significantly more susceptible to lambda-cyhalothrin (LC(50) = 0.00013 and 0.00016 mg/L) than fenitrothion (LC(50) = 0.0009 and 0.004 mg/L). As expected, the pyrethroid and organophosphorous insecticides were far more potent than the crude C. glaucophylla extracts. The steam distilled extract was fractionated and the major components guaiol and citronellic acid were identified and tested. Activities for these major components were lower than observed for the distillate. Minor components include lactones such as eldanolide, and future testing of minor components may indicate the active component.

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.