Oviposition-stimulant and ovicidal activities of Moringa oleifera lectin on Aedes aegypti.

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 (pConclusions/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

Top view of glass vessels used in oviposition assay.

<p>A filter paper cone was placed covering the inner of each vessel to provide a support for oviposition. Next, the vessels were filled with distilled water (A, control) or WSMoL at 0.1 mg/mL in distilled water (B).</p

Ovicidal activity on <i>A. aegypti</i> stored eggs of <i>M. oleifera</i> seed extract, 0–60 protein fraction and WSMoL.

a<p>Effective concentrations of proteins required to reduce in 50% (EC₅₀) and 99% (EC₉₉) the hatching of <i>A. aegypti</i> eggs in 72 h calculated by probit analysis with a reliability interval of 95%. Values in square brackets represent the lower and upper endpoints for reliability interval.</p

Percentage of unhatched stored eggs after incubation with seed extract (A), 0–60 protein fraction (B) and WSMoL (C) for 72 h.

<p>Percentage of unhatched stored eggs after incubation with seed extract (A), 0–60 protein fraction (B) and WSMoL (C) for 72 h.</p

Visualization of <i>A. aegypti</i> fresh and stored eggs exposed or not to WSMoL in stereomicroscope (x80) after clearing of the heavily pigmented chorion with 5% sodium hypochlorite.

<p>(A) Fresh egg laid and maintained in distilled water (control). (B) Fresh egg laid and maintained in WSMoL (0.1 mg/mL). (C) Stored egg which was not treated with any solution. (D) Stored egg that did not hatch after incubation with WSMoL at EC₉₉ (0.3 mg/mL) for 72 h. (h) head; (a) abdomen.</p

Effect of <i>M. oleifera</i> seed preparations (0.1 mg/mL of protein) on oviposition and egg hatching of <i>Aedes aegypti</i>.

<p>(A) Mean of eggs laid by <i>A. aegypti</i> gravid females in distilled water and <i>M. oleifera</i> seed preparations. The oviposition response was evaluated by double-choice bioassays. Three distinct assays (“control vs. seed extract”, “control vs. 0–60 protein fraction” and “control vs. WSMoL”) were performed separately, each one with its respective control. The oviposition response was expressed as: % oviposition  = 100× [(number of eggs in sample vessel) / (number of eggs in sample and control vessels)]. (B) Hatching rate (%) of eggs laid by gravid females during the oviposition assays in distilled water and <i>M. oleifera</i> seed preparations. (*) indicates significant differences (p<0.05) between control and test groups.</p