Field evaluation of biodegradable controlled release formulation of fenthion against Mansonia mosquitos

Controlled release monolithic formulation of fenthion, an organophosphorus mosquito larvicide, prepared by the physical entrapment of the active agent into biodegradable polymer matrices was evaluated against Mansonia mosquito larvae breeding in hydrophytes infested coconut husk retting ponds. Field evaluation was carried out at two application rates viz, 2.5 and 1.0 ppm. Absolute control of larval breeding was observed for 25 and 17 weeks and over 50% reduction in breeding density was observed for another 3 and 2 weeks for the respective application rates of 2.5 and 1.0 ppm. The bioassay carried out with the water samples collected from the ponds treated at 2.5 ppm against the fourth instar larvae of Mansonia annulifera showed larval mortality of more than 95% for 14 weeks and 80-95% from 15 to 25th week. The concentration of fenthion in the treated ponds was found to vary between 0.006 and 0.095 ppm during the evaluation period.