Evaluation of larvicidal and ovicidal effect of mundulea Sericea in the control of culex quinquef asciatus
Mwangemi, Arthur Mwanjulu
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Vector surveillance and control are crucial to any effective and sustainable suppression programmes of vector-borne diseases. Culex quinquefasciatus is not only a biting nuisance in urban areas but also an important vector for lymphatic filariasis in Kenya. In urban areas it breeds in various sites such as wet pit latrines, cess pits, cess pools, blocked open drains, discarded tyres and tins containing polluted water. Various control methods such as conventional insecticides have been used to target C. quinquefasciatus larvae but with little success due to larval resistance. This study determined the efficacy of a plant Mundulea sericea in the control of C. quinquefasciatus in the laboratory, Semi field and field habitats. Various crude extract samples of M sericea from Coastal region and Western Kenya were applied in 100 mls cups with thirty third instar larvae in three replicates in the laboratory. One control set up was treated with alpha cypermethrine (Bestox) while another had no treatment and each was replicated three times. Mortality was monitored for 120 hours at 24 hour intervals. Set up with five rafts of the Culex mosquito were similarly prepared and treated with the Coast sample crude extract. The LC90value was calculated to determine the most effective isolate. Sample with higher efficacy was further tested in the Semi field and field conditions. Five experimental sites (A, B, C, 0 and E) prepared in the Semi field and five sites with stagnant wastewaters identified in the field were replicated three times. Sites AI, A2 and A3, were treated with half LC90 dosage while the B replicate sites were treated with exact LC90 value. The C sites were treated with double LC90 value. Alpha cypermethrine was applied in the 0 sites at the rate of 1Omls/20liters of water while the E sites were negative control, with no treatment. Larval and pupal densities were determined after treatment at 24 hours interval for 72 hours and then after 7 and 14 days. An average of O.28g crude extract for Coast sample was obtained as LC90while the western sample produced 0.55g in laboratory bioassay. Only negligible number of larvae died in the control without treatment while all larvae died within 24 hours in alpha cypermethrine treated set up. Coast sample mortality mean was significantly higher than that from Western (t (178) = 5.36,p=0.000, a =0.05). Factorial ANOV A showed significance in larval and pupal mortality with every concentration of Coast sample crude extract applied relative to controls in semi field (F (290,314) =2.58, P = 0.0378, a =0.05) and in the field (F (285,309) =8.20, p=O.OOOO,a =0.05). The mosquito larvae were recovered after 7 days with only 1st lnstar present. A complete cycle recovery with all immature stages was realized after 14 days. There was also statistical significance in mortality variations among various instars of larvae and pupa (F (290,314) =2.77, P = 0.0276, a =0.05). However there was no significant interaction between crude extracts applied and larval instars and pupa to cause mortality in the semi field (F (290,314) =1.37, P = 0.1561, a =0.05). No eggs hatched at 0.126g concentration of alpha cypermethrine. oast sample had a higher efficacy of 0.28g per lOOmis of water compared to 0.5g of the sample from Western Kenya both being average LC90 values. In both Semi field and field habitats, double LC90 was more effective than any other M sericea concentrations. In addition, 0.3g of crude extract from Coast sample completely hindered hatchability of C. quinquefasciatus eggs both in the laboratory and in the semi field treatment relative to the controls (I (26) = 3.0987, p=0.0046, a =0.05.). This implies therefore both Coast and Western samples of M sericea have larvicidal effect against C. quinquefasciatus larvae and pupa and Coast sample also has ovicidal effect against the eggs. This study therefore recommends the adoption of M sericea crude extract as a biological larvicide and ovicide to control C. quinquefasciatus.