Abstract
BackgroundNatural insecticides against the vector mosquito Aedes aegypti have been the object of research due to their high level of eco-safety. The water-soluble Moringa oleifera lectin (WSMoL) is a larvicidal agent against A. aegypti. This work reports the effects of WSMoL on oviposition and egg hatching of A. aegypti.Methodology/Principal FindingsWSMoL crude preparations (seed extract and 0–60 protein fraction), at 0.1 mg/mL protein concentration, did not affect oviposition, while A. aegypti gravid females laid their eggs preferentially (73%) in vessels containing isolated WSMoL (0.1 mg/mL), compared with vessels containing only distilled water (control). Volatile compounds were not detected in WSMoL preparation. The hatchability of fresh eggs deposited in the solutions in the oviposition assay was evaluated. The numbers of hatched larvae in seed extract, 0–60 protein fraction and WSMoL were 45±8.7 %, 20±11 % and 55±7.5 %, respectively, significantly (p<0.05) lower than in controls containing only distilled water (75–95%). Embryos were visualized inside fresh control eggs, but not within eggs that were laid and maintained in WSMoL solution. Ovicidal activity was also assessed using stored A. aegypti eggs. The protein concentrations able to reduce the hatching rate by 50% (EC50) were 0.32, 0.16 and 0.1 mg/mL for seed extract, 0–60 protein fraction and WSMoL, respectively. The absence of hatching of stored eggs treated with WSMoL at 0.3 mg/mL (EC99) after transfer to medium without lectin indicates that embryos within the eggs were killed by WSMoL. The reduction in hatching rate of A. aegypti was not linked to decrease in bacteria population.Conclusions/SignificanceWSMoL acted both as a chemical stimulant cue for ovipositing females and ovicidal agent at a given concentration. The oviposition-stimulant and ovicidal activities, combined with the previously reported larvicidal activity, make WSMoL a very interesting candidate in integrated A. aegypti control.
Highlights
Aedes aegypti Linnaeus is a domestic, daytime mosquito that breeds preferably in water storage containers, discarded plastic vials, and automobile tyres [1]
No precipitate formation was observed after addition of 0–60 protein fraction to acidified barium chloride solution, revealing that no residual ammonium sulphate remained in the sample
water-soluble Moringa oleifera lectin (WSMoL) was isolated by chitin chromatography and was the most hemagglutinating preparation
Summary
Aedes aegypti Linnaeus is a domestic, daytime mosquito that breeds preferably in water storage containers, discarded plastic vials, and automobile tyres [1]. This mosquito has great importance in tropical and subtropical countries, since it is the vector of yellow and dengue fevers. Synthetic chemicals, mainly pyrethroids, carbamates and organophosphates are used to control adults, larvae, pupae and eggs of A. aegypti. These compounds pose high environmental risks, due to adverse effects on human and nontarget organisms [4,5]. This work reports the effects of WSMoL on oviposition and egg hatching of A. aegypti
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