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Larvicidal effects of a neem (Azadirachta indica) oil formulation on the malaria vector Anopheles gambiae.

Okumu FO, Knols BG, Fillinger U - Malar. J. (2007)

Bottom Line: Costs could be reduced if larvicides could be manufactured locally.Significant reductions on growth indices and pupation, besides prolonged larval periods, were observed at neem oil concentrations above 8 ppm.Neem oil has good larvicidal properties for An. gambiae s.s. and suppresses successful adult emergence at very low concentrations.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Nairobi, School of Biological Sciences, Nairobi, Kenya. fros2001@hotmail.com <fros2001@hotmail.com>

ABSTRACT

Background: Larviciding is a key strategy used in many vector control programmes around the world. Costs could be reduced if larvicides could be manufactured locally. The potential of natural products as larvicides against the main African malaria vector, Anopheles gambiae s.s was evaluated.

Methods: To assess the larvicidal efficacy of a neem (Azadirachta indica) oil formulation (azadirachtin content of 0.03% w/v) on An. gambiae s.s., larvae were exposed as third and fourth instars to a normal diet supplemented with the neem oil formulations in different concentrations. A control group of larvae was exposed to a corn oil formulation in similar concentrations.

Results: Neem oil had an LC50 value of 11 ppm after 8 days, which was nearly five times more toxic than the corn oil formulation. Adult emergence was inhibited by 50% at a concentration of 6 ppm. Significant reductions on growth indices and pupation, besides prolonged larval periods, were observed at neem oil concentrations above 8 ppm. The corn oil formulation, in contrast, produced no growth disruption within the tested range of concentrations.

Conclusion: Neem oil has good larvicidal properties for An. gambiae s.s. and suppresses successful adult emergence at very low concentrations. Considering the wide distribution and availability of this tree and its products along the East African coast, this may prove a readily available and cheap alternative to conventional larvicides.

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Related in: MedlinePlus

Percentage larval mortality, pupation and adult emergence (as proportion of original numbers tested) of 3rd-4th instar larvae of An. gambiae following exposure to various concentrations (0.5–32 ppm) of neem oil (N) or corn oil (C). Adult emergence values are percentages of the total number of mosquitoes tested as larvae.
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Figure 1: Percentage larval mortality, pupation and adult emergence (as proportion of original numbers tested) of 3rd-4th instar larvae of An. gambiae following exposure to various concentrations (0.5–32 ppm) of neem oil (N) or corn oil (C). Adult emergence values are percentages of the total number of mosquitoes tested as larvae.

Mentions: Neem oil was highly larvicidal at high concentrations (32 ppm), but this activity declined progressively as the dose decreased (Figure 1). Corn oil had little if any larvicidal properties at any concentration tested. At concentrations above 16 ppm of the neem oil formulation, over 80% of the observed mortality occurred within the first 72 hrs, while at lower concentrations the rate of mortality was very slow and some larvae, in spite of being 3rd or 4th instar, lived as long as 8 days before they either pupated or died. The median anti-larval potency (LC50) of the neem oil formulation after 8 days was 10.7 ppm, and the LC90 was 24.1 ppm (Table 1). This was 4.7 times lower than the corn oil formulation, which showed an LC50 of 50.7 ppm. The concentration of neem oil that induced median emergence inhibition (EI50) was 6.4 ppm while the EI90 was 17.4 ppm. Table 1 shows that the EI50 value of the neem oil formulation was approximately 8 times lower than that of the corn oil formulation. At 32 ppm the neem formulation inhibited 99.3% of emergence. Whereas the adult emergence steadily increased with decreasing concentrations of the neem oil formulation, there were no observable increments with the corn oil formulation (Figure 1).


Larvicidal effects of a neem (Azadirachta indica) oil formulation on the malaria vector Anopheles gambiae.

Okumu FO, Knols BG, Fillinger U - Malar. J. (2007)

Percentage larval mortality, pupation and adult emergence (as proportion of original numbers tested) of 3rd-4th instar larvae of An. gambiae following exposure to various concentrations (0.5–32 ppm) of neem oil (N) or corn oil (C). Adult emergence values are percentages of the total number of mosquitoes tested as larvae.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC1887534&req=5

Figure 1: Percentage larval mortality, pupation and adult emergence (as proportion of original numbers tested) of 3rd-4th instar larvae of An. gambiae following exposure to various concentrations (0.5–32 ppm) of neem oil (N) or corn oil (C). Adult emergence values are percentages of the total number of mosquitoes tested as larvae.
Mentions: Neem oil was highly larvicidal at high concentrations (32 ppm), but this activity declined progressively as the dose decreased (Figure 1). Corn oil had little if any larvicidal properties at any concentration tested. At concentrations above 16 ppm of the neem oil formulation, over 80% of the observed mortality occurred within the first 72 hrs, while at lower concentrations the rate of mortality was very slow and some larvae, in spite of being 3rd or 4th instar, lived as long as 8 days before they either pupated or died. The median anti-larval potency (LC50) of the neem oil formulation after 8 days was 10.7 ppm, and the LC90 was 24.1 ppm (Table 1). This was 4.7 times lower than the corn oil formulation, which showed an LC50 of 50.7 ppm. The concentration of neem oil that induced median emergence inhibition (EI50) was 6.4 ppm while the EI90 was 17.4 ppm. Table 1 shows that the EI50 value of the neem oil formulation was approximately 8 times lower than that of the corn oil formulation. At 32 ppm the neem formulation inhibited 99.3% of emergence. Whereas the adult emergence steadily increased with decreasing concentrations of the neem oil formulation, there were no observable increments with the corn oil formulation (Figure 1).

Bottom Line: Costs could be reduced if larvicides could be manufactured locally.Significant reductions on growth indices and pupation, besides prolonged larval periods, were observed at neem oil concentrations above 8 ppm.Neem oil has good larvicidal properties for An. gambiae s.s. and suppresses successful adult emergence at very low concentrations.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Nairobi, School of Biological Sciences, Nairobi, Kenya. fros2001@hotmail.com <fros2001@hotmail.com>

ABSTRACT

Background: Larviciding is a key strategy used in many vector control programmes around the world. Costs could be reduced if larvicides could be manufactured locally. The potential of natural products as larvicides against the main African malaria vector, Anopheles gambiae s.s was evaluated.

Methods: To assess the larvicidal efficacy of a neem (Azadirachta indica) oil formulation (azadirachtin content of 0.03% w/v) on An. gambiae s.s., larvae were exposed as third and fourth instars to a normal diet supplemented with the neem oil formulations in different concentrations. A control group of larvae was exposed to a corn oil formulation in similar concentrations.

Results: Neem oil had an LC50 value of 11 ppm after 8 days, which was nearly five times more toxic than the corn oil formulation. Adult emergence was inhibited by 50% at a concentration of 6 ppm. Significant reductions on growth indices and pupation, besides prolonged larval periods, were observed at neem oil concentrations above 8 ppm. The corn oil formulation, in contrast, produced no growth disruption within the tested range of concentrations.

Conclusion: Neem oil has good larvicidal properties for An. gambiae s.s. and suppresses successful adult emergence at very low concentrations. Considering the wide distribution and availability of this tree and its products along the East African coast, this may prove a readily available and cheap alternative to conventional larvicides.

Show MeSH
Related in: MedlinePlus