Integrated Mosquito Larval Control: Toxicity and Safety Evaluation of Larvicides on Guppy Fish (Poecilia Reticulata)

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Anogwih, J.A
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Toxicity and safety of selected larvicides on Poecilia reticulata, a predator fish, was investigated in the control of mosquito larvae using integrated approach. Preliminary studies were carried out to establish an optimum feeding density for P. reticulata by introducing Culex quinquefasciatus and Anopheles gambiae larvae respectively to the predatory fish at different population levels and time intervals. Prey preference of P. reticulata was determined in the presence of Chironomid sp., Culex sp. and Eudrillus sp., that naturally co-exist with the fish by introducing 30 of each prey type to different population levels of the fish. Acute toxicity tests were carried out to determine the effect of three larvicides: chlorpyrifos, actellic and spinosad larvicides on P. reticulata and the mosquito larvae species respectively. Thereafter, blood samples were collected from the gill epithelial cells of the fish exposed in vivo for 28 days to sub-lethal concentrations of 1/29th, 1/12th, and 1/3rd of the 24 hLC50 values of actellic against P. reticulata to determine the cytogenotoxic effects using Giemsa assay. To investigate the behavioral, genotoxic and ultrastructural changes in P. reticulata, the fish were exposed for 28 days to low concentrations of the test larvicides capable of killing 30%, 50% and 70% of Culex larvae. Poecilia reticulata and Cx. quinquefasciatus in ratios of 1:35; 5:70 and 10:350 were exposed for 24 h at the established low concentrations in six replicates. The results showed that the prey consumption by P. reticulata increased significantly with predator-prey density and time interval (P<0.05). The fish competed for the preys prior to feeding on them of which, Chironomid sp. was the most vulnerable. Spinosad, unlike chlorpyrifos and actellic, showed no lethal toxic effect on P. reticulata but caused an appreciable mortality in Anopheles and Culex larvae with 24 hLC50 values of 59.34 μgL-1 and 73.06 μgL-1 respectively. Sub-lethal concentrations of spinosad and actellic induced significant micronuclei in the fish gill xxi cells (P<0.05) with actellic having a higher potential to cause mutagen-induced cytotoxicity in the fish. The three larvicides failed to significantly induce micronuclei in the fish using the Acridine orange assay (P>0.05). Chlorpyrifos caused the highest behavioral changes in the fish exhibiting the following symptoms: heamorrhage, scoliosis and loss of equilibrium with increasing concentration of the larvicide. Pycnotic nuclei, loss of cristae in mitochondria and degraded cytoplasm were some of the ultrastructural changes that occurred in the intestinal cells of the exposed fish. There were no observed adverse changes in the fish cells exposed to spinosad at 49 μgL-1. The integration of P.reticulata and spinosad significantly decreased the population of Cx. quinquefasciatus at all the feeding densities sampled when compared to actellic and chlorpyrifos (P<0.05). The population of Cx. quinquefasciatus reduced only at the lowest concentration of actellic and at predator-prey densities of 5:70 and 10:350 respectively. Integrating spinosad at 49 μgL-1 with P. reticulata at predator density of 10:350 gave the most effective mosquito larval control with minimal adverse effect on the non-target fish species
A Thesis Submitted to the School of Postgraduate Studies, University of Lagos
Toxicity , Control -Mosquito Larvae , Predator density , Tests , Research Subject Categories::NATURAL SCIENCES::Biology::Organism biology
Anogwih, J.A (2012). Integrated Mosquito Larval Control: Toxicity and Safety Evaluation of Larvicides on Guppy Fish (Poecilia Reticulata). A Thesis Submitted to University of Lagos School of Postgraduate Studies Phd Thesis and Dissertation, 179pp.