EVALUATION OF RESIDUAL EFFECTS OF PESTICIDES ON FRUIT FLIES (Drosophila melanogaster)

Abstract

Pesticides are used worldwide to control agricultural pests, but their non-target effects on beneficial organisms remain a growing environmental concern. This study evaluates the residual effects of four commonly used pesticides on fruit flies (Drosophila melanogaster) as a model non-target organism. Adult flies were exposed to each pesticide at a 1-10 mmol concentration under controlled conditions, with three replicates per treatment.  Acute toxicity, fecundity eclosion and enzyme activities such as catalase (CAT) and superoxide dismutase (SOD) were measured to assess physiological stress and toxicity using residual film contact method. The results showed that all pesticides induced varying levels of toxicity compared to the untreated control. Lambda-cyhalothrin with the steepest slope (3.45), was most rapid n causing mortality over time with the LC₅₀ value of 4.18 mmol at 72h, 5.23 mmol at 48h and 7.45 mmol at 24h and LC₉₀ of 7.05 mmol at 72h, 8.92 mmol at 48h and 10 mmol at 24h. Glyphosate was the least with LC₅₀ of 5.12 mmol at 72h, 7.83 mmol at 48h and 10 mmol at 24h. Imidacloprid caused the highest reduction in the number eggs laid per female with the mean value of 11.67±4.48 while the least was paraquat (22±5.49). There was no significant difference across the treatment groups (F = 0.825, df = 4, P> 0.539). Imidacloprid was the most toxic against fruit flies eclosion with 100±0.00 % mortality and 0.00 ±0.00% eclosion while paraquat was the least with 81.67±10.93% mortality and 18.67±10.93% eclosion with observed significant difference across the treatment groups (F = 7.554, df = 4, P< 0.005). Glyphosate induced the highest oxidative stress with the SOD and catalase activities of 253.67±82.3 and 215.8±92.9 while the least was lambda-cyhalothrin (742.57±255.6 and 355.4±40.3), respectively. Therefore, there was a significant difference in the SOD activity across the treatment group (F = 39.021, df = 4, P<0.001) likewise catalase activities (F = 7.641, df = 4, P<0.004). These findings indicate that even pesticides intended for specific pests can adversely affect non-target organisms. Therefore, careful selection and use of pesticides are essential to reduced ecological risks and maintain environmental balance.