The larvicidal activity of Agave sisalana against L4 larvae of Aedes aegypti is mediated by internal necrosis and inhibition of nitric oxide production.

Dengue is a viral disease that affects about 50 million people per year around the world. The aim of this study was to investigate the larvicidal activity of Agave sisalana crude extract in order to develop a new insecticide against Aedes aegypti. In larvicidal activity assays, fourth-stage Ae. aegypti larvae were exposed to different concentrations of A. sisalana crude extract for 3, 6, 12, and 24 h for determining the LC50. Next, we explored its cytotoxic activity by flow cytometry. Furthermore, histological alterations were confirmed by histopathological analysis, and the nitric oxide (NO) production by hemocytes was checked after different periods of exposure to A. sisalana crude extract. The LC50 was 4.5 ± 0.07 mg/mL. In addition, flow cytometry revealed an increase of cellular necrosis (21 and 16.5 % after 12 and 24 h, respectively) in larvae that were exposed to A. sisalana crude extract. The histological analysis revealed cell lysis and destruction of the peritrophic membrane. Furthermore, there was a reduction in the concentration of NO in the hemolymph from larvae exposed to A. sisalana crude extract after 3, 6, and 24 h (5.3 ± 4.3 vs. 22.7 ± 5.2 µM, 4.3 ± 5.5 vs. 25.4 ± 6.6 µM, and 6 ± 1.7 vs. 37.1 ± 7.8 µM, respectively). Our findings show that A. sisalana crude extract constitutes an effective larvicidal agent against Ae. aegypti larvae due to its necrotizing activity in hemocytes and inhibition of the NO production.

Larvicidal & emergence inhibitory activities of NeemAzal T/S 1.2 per cent EC against vectors of malaria, filariasis & dengue.

BACKGROUND & OBJECTIVE: Vector control, using agents of chemical origin, continues to be practiced in the control of vector borne diseases. However, due to some drawbacks including lack of selectivity, environmental contamination, and emergence and spread of vector resistance, development of natural products for vector control has been a priority in this area. In the present study we evaluated the larvicidal and emergence inhibitory activities of a neem based formulation Neem Azal T/S 1.2 per cent EC against the vectors of malaria, filariasis and dengue. METHODS: Larvicidal and emergence inhibition (EI) activity of a neem formulation, NeemAzal T/S 1.2 per cent EC, was studied in the laboratory respectively against early 4(th) and early 3(rd) instar larvae of Anopheles stephensi, Culex quinquefasciatus and Aedes aegypti following standard procedures. RESULTS: Among the three vector species studied, An. stephensi was highly susceptible to NeemAzal T/S as revealed by the LC(50) and LC(90) values (1.92 and 2.76 ppm). The formulation produced an overall mortality or inhibition of emergence of 90 per cent (EI(90), when 3(rd) instar larvae were treated) at 0.046, 0.208 and 0.866 ppm in An. stephensi, Cx. quinquefasciatus and Ae. aegypti, respectively. The corresponding EI(50) values were 0.006, 0.048 and 0.249 ppm. On treatment, NeemAzal T/S induced certain morphogenetic abnormalities, broadly characterized in five types, in larvae, pupae and adults of all the three vector species. The percentage of dead specimens of any stage showing morphogenetic abnormalities was the maximum in Cx. quinquefasciatus (14.4%; n=2113) followed by Ae. aegypti. INTERPRETATION & CONCLUSION: Our results indicated that because of its emergence inhibition activity, NeemAzal T/S 1.2 per cent EC could be a promising candidate for the use in integrated vector management programme and replace chemical insecticides.

Açäo larvicida de extrato bruto etanólico de Magonia pubescens St.Hil. (tingui-do-cerrado), sobre o Aedes aegypti(Lin.) em laboratório / Larvicid action crude ethanol extract of Magonia pubescens St.Hil.(tingui-do-cerrado), on the Aedes aegypti(Lin.), dengue's main vector

Realizaram-se testes biológicos com extrato bruto etanólico (e.b.e.) de Magonia pubescens St. Hill., (tingui-do-cerrado)(Sapindaceae) para verificar a açäo larvicida sobre o Aedes aegypti(Lin.). Os extratos foram obtidos a partir de cada parte da planta: casca do caule, envoltório da semente e semente. Após ter sido coletado, o material foi dessecado em estufa de ar forçado a 40§C, moído, percolado em etanol por 10 dias, filtrado em papel filtro qualitativo, concentrado em evaporador rotativo e dessecado em pistola à vácuo. Após a obtençäo do e.b.e. de cada parte da planta, este foi dissolvido em água, em diferentes concentraçöes e testados com larvas de 4§ estádio de A.aegypti para determinar a DL50, que foi de 35, 55 e 150mg do e.b.e./100ml de água destilada, respectivamente, para semente, envoltório da semente e casca do caule. Cada experimento foi realizado com 20 frascos descartáveis, com capacidade para 30ml, com uma larva em cada um deles e observados por 24 horas. As larvas foram criadas em câmara biológica climatizada a 28ñ1§c, umidade relativa de 80ñ5(pôr cento) e fotofase de 12 horas. Os testes biológicos com os e.b.e. foram realizados em outra câmara, climatizada similarmente. Entre os experimentos realizados, os e.b.e. da semente e seu envoltório, mostraram-se mais eficientes larvicidas do que os e.b.e. da casca do caule