The toxicological profile of three larvicides for integrated mosquito larval control

ABSTRACT

Toxicity and safety of selected larvicides on Poecilia reticulata (guppy) was investigated for integrated mosquito larval control. To assess the behavioural, genotoxic and ultrastructural changes in guppy, the fish were exposed for 28 days to low concentrations of the three test larvicides capable of killing 30%, 50% and 70% population of Culex quinquefasciatus following acute toxicity studies. Spinosad, unlike chlorpyrifos and actellic showed no lethal toxic effect on guppy but caused an appreciable mortality in Anopheles gambiae s.s and Cx. quinquefasciatus larvae with 24h LC50 values of 59.34 μgL^-1 and      73.06 μgL^-1 respectively. The three larvicides failed to significantly induce micronuclei in the fish (P>0.05). Chlorpyrifos caused the greatest behavioural changes in the fish exhibiting the following symptoms: heamorrhage, scoliosis and loss of equilibrium at increasing concentration. Marked damage characterized by pycnotic nuclei, cell ruptures, dense and degraded cytoplasm was found in the exposed intestinal cells of guppy except with spinosad treatment at 49 μgL^-1 where minimal damage was recorded. Spinosad can only be compatible with guppy for integrated mosquito larval control at concentration not greater than 49 μgL^-1.

Keywords: Larvicides, Poecilia reticulata, Anopheles gambiae s.s., Culex quinquefasciatus