Research Article
Anogwih JA, Saliu JK, Linto
Abstract
Background: The compatibility of spindor dust (spinosad), a bio-rational larvicide derived from the fermentation of a soil bacterium Saccharopolyspora spinosa, was investigated on the mosquito fish, Poecilia reticulata, and larvae of both Anopheles gambiae s.s. and Culex quinquefasciatus mosquitoes. Methods: Three replicates of each to different concentrations of spinosad dust under static bioassay were performed to determine the acute toxicity of the larvicide on each organism. To investigate the genotoxic and ultrastructural changes in P. reticulata, the fish were exposed for 28 days to low concentrations of the test larvicide capable of killing 30% and 70% of Cx. quinquefasciatus larvae. Thereafter, gill and intestinal cells were removed at days 3 and 28 respectively, and then processed for epifluorescent and transmission electron microscopic studies. Results: Spinosad showed no lethal toxic effect on P. reticulata but caused an appreciable mortality to Anopheles and Culex larvae with 24h LC50 values of 59.34 μgL-1 and 73.06 μgL-1 respectively. The larvicide failed to significantly induce micronuclei in the fish as determined with acridine orange assay (P>0.05). Marked damage characterised by pycnotic nuclei, loss of cristae in mitochondria, dense and degraded cytoplasm was mostly found in the exposed intestinal cells of the fish and the damage severity increased with increasing concentration of spinosad. Conclusion: Spinosad at 49 μgL-1 seems to be the threshold above which severe damage occurred in the fish. Therefore, spinosad is only compatible with P. reticulata for integrated mosquito larval control at concentration not greater than 49 μgL-1.