Neem by-products in the fight against mosquito-borne diseases:Biotoxicity of neem cake fractions towards the rural malaria vector Anopheles culicifacies(Diptera:Culicidae)

Objective: To evaluate the ovicidal, larvicidal and adulticidal potential of neem cake fractions of different polarity against the rural malaria vector Anopheles culicifacies(An.culicifacies).Methods: Neem cake fractions' total methanol extract(NTMeOH), total ethyl acetate extract(NTAc OEt), ethyl acetate fraction after repartition with NTMe OH(NRAc OEt),butanol fraction after repartition with NTMeOH(NRBuOH), and aqueous fraction after repartition of NTMeOH(NRH2O) were tested against An. culicifacies eggs, fourth instar larvae and adults.Results: In larvicidal experiments, NTMeOH, NTAcOEt, NRAcOEt, NRBuOH and NRH2O achieved LC50 values of 1.32, 1.50, 1.81, 1.95 and 2.54 mg/L, respectively. All fractions tested at 150 mg/L were able to reduce egg hatchability of more than 50%, with the exception of NTAc OEt and NRAc OEt. In adulticidal assays, NTMeOH, NTAcOEt,NRAcOEt, NRBuOH and NRH2O achieved LC50 values of 3.01, 2.95, 3.23, 3.63 and3.00 mg/L, respectively.Conclusions: Overall, this study suggests that the methanolic fractions of neem cake may be considered as a new and cheap source of highly effective compounds against the rural malaria vector An. culicifacies.

Insecticide susceptibility in larval populations of the West Nile vector Culex pipiens L.(Diptera: Culicidae) in Saudi Arabia

Objective: To investigate the susceptibility to some conventional and non-conventional insecticides in laboratory and field larval populations of the West Nile vector Culex pipiens L.(Cx. pipiens), the dominant species in Jeddah Province, Saudi Arabia.Methods: The tested conventional insecticides were Actikil and Pesgard, while the nonconventional ones were Bacilod, Dudim and Baycidal. Probit analysis and photomicroscopical observations were carried out to shed light on acute toxicity in laboratory and field Cx. pipiens strains.Results: Cx. pipiens were more susceptible to Pesgard(LC50: 0.045 and 0.032 mg/L)than Actikil(0.052 and 0.038 mg/L) and Bacilod(0.129 and 0.104 mg/L), for the field and laboratory strains, respectively. Results showed that treatments with the chitin synthesis inhibitor Dudim and Baycidal evoked morphological effects similar to those induced by other insect growth regulators. According to IC50 values obtained(concentration which to inhibit the emergence of 50% of mosquito adults), the compound Dudim(0.000 3 and 0.000 1 mg/L) was more effective against Cx. pipiens L. mosquitoes than Baycidal(0.000 4 and 0.000 3 mg/L) for both the field and laboratory strains, respectively.Conclusions: Our results provide baseline data to enhance control programs and orient public health decisions on the selection of pesticides against mosquito vectors in Saudi Arabia.

Larvicidal efficacy of Catharanthus roseus Linn.(Family:Apocynaceae)leaf extract and bacterial insecticide Bacillus thuringiensis against Anopheles stephensi Liston.

Objective:To explore the larvicidal activity of Catharanthus roseus(C.roseus) leaf extract and Raeillus thuringiensis(B.thuringiensis) against the malarial vector Anopheles stephensi(An. stephensi),when being used alone or together.Methods:The larvicidal activity was assayed at various concentrations under the laboratory and field conditions.The LC_(50) and LC_(90) values of the C.roseus leaf extract were determined by probit analysis.Results:The plant extract showed larvicidal effects after 24 h of exposure;however,the highest larval mortality was found in the petroleum ether extract of C.roseus against the first to fourth instars larvae with LC_(50)=3.34,4.48, 5.90 and 8.17 g/L,respectively;B.thuringiensis against the first to fourth instars larvae with LC_(50)=1.72.1.93.2.17 and 2.42 g/L.respectively:and the combined treatment with LC_(50)=2.18.2.41. 2.76 and 3.22 g/L,respectively.No mortality was observed in the control.Conclusions:The petroleum ether extract of C.roseus extract and B.thuringiensis have potential to be used as ideal eco-friendly agents for the control of An.stephensi in vector control programs.The combined treatment with this plant crude extract and bacterial toxin has better larvicidal efficacy against An.stephensi.