The effect of exposure to heat,  UV-rays and sunlight on the degradation of fenitrothion and malathion were studied. It was found that fenitrothion insecticide residues was more persistence than malathion insecticide residues and both showed progressive loss as temperature and prolongation of exposure period increased, this indicates that the interval between successive sprays should be shorter at high temperature and vice versa. Photodegradation with UV-rays was positively correlated with exposure  period  and  chemical  structure  of  insecticide,   malathion degraded faster than fenitrothion in this respect. Sunlight was more effective than UV-rays in accelerating the photodecomposition of fenitrothion and malathion residues.