Toxicological Evaluation of Some Insecticides and Their Combined Action with Azadirachtin against the Lesser Mealworm Alphitobius Diaperinus (Panzer)

Abstract

The toxicity of five (5) commercially formulated insecticides viz. Fenitrothion (organophosphate); Thiodicarb (Carbamet); Deltamethrin (Pyrethroid), Imidacloprid (Neonecotinoide) and Nimbicidine (Azadirachtin) were investigated following residual film method (RFM) and treated flour method (TFM). Adults and larvae (1, 10, 20, 30 and 40-days old) of Alphitobius diaperinus Panzer were used in the experiment. The mortality data were recorded after 24, 48 and 72 hours of exposure. All tested insecticides were found to be toxic on the beetles. The insecticides were moderately and less toxic on adults in residual film method having LD50 values as 3082.80 (Imidacloprid), 3033.83 (Fenitrothion), 1229.48 (Deltamethrin), 376.39 (Thiodicarb), and 61.85 (Azadirachtin) µg/cm2 after 24 hrs exposure. Azadirachtin and thiodicarb were the most toxic and fenitrothion and imidacloprid were found to be comperatively less toxic to adults in RFM test. The order of toxicity for adults was Azadirachtin > Thiodicarb> Deltamethrin > Fenitrothion > Imidacloprid. The LD50 values for the mature larvae (40 days old) at same test were 361.78 (Deltamethrin), 257.76 (Fenitrothion), 215.48 (Imidacloprid), 78.47 (Thiodicarb) and 25.28 (Azadirachtin) µg/cm2 after 24 hours respectively. The toxicity was higher than that of adults and the order of toxicity was Azadirachtin > Thiodicarb > Imidacloprid> Fenitrothion> Deltamethrin. The LD50 values for the newly hatched larvae (1 day old) at same test were 49.74 (Fenitrothion), 19.62 (Imidacloprid), 4.49 (Azadirachtin), 4.43 (Thiodicarb) and 3.05 (Deltamethrin) µg/cm2 after 24 hours exposure. Most of the insecticides were found to be highly toxic on 1 day old larvae. The toxicity was higher than mature larvae and the order of toxicity was Deltamethrin> Thiodicarb > Azadirachtin > Imidacloprid> Fenitrothion. In Residual Film Method (RFM) imidacloprid was less toxic on adults. Deltamethrin was less toxic on mature larvae but highly toxic on newly hatched larvae. Fenitrothion was less toxic on newly hatched larvae than other insecticides. Azadirachtin and thiodicarb were found highly toxic on all stages of beetles. In treated food method (TFM), the LD50 values after 24 hours for adults were 2044.41 (Deltamethrin), 901.08 (Fenitrothion), 579.83 (Azadirachtin), 359.46(Imidacloprid) and 194.23 (Thiodicarb) ppm. For the mature larvae these values were 1095.90 (Deltamethrin), 436.41 (Fenitrothion), 340.98 (Azadirachtin), 307.99 (Imidacloprid) and 49.28 (Thiodicarb)ppm. For the newly hatched larvae these values were 168.90 (Deltamethrin), 161.34 (Fenitrothion), 81.42 (Azadirachtin), 22.39 (Imidacloprid) and 14.62 (Thiodicarb)ppm. In treated food method, thiodicarb was the most toxic, and deltamethrin was the least toxic against all stages of beetles. The order of toxicity on all stages of beetles was, Thiodicarb > Imidacloprid> Azadirachtin> Fenitrothion> Deltamethrin. In all type of methods for the larvae and adults, the toxicity of all insecticides were increased with time and decreased with age of insects. Synergistic effect with azadirachtin in combination with all insecticides was evaluated. The synergistic effects were calculated by using co-toxicity coefficient (> 100) values. The interaction between insecticides and synergist was analyzed for co-toxicity co-efficient and through plotting isoboles of the LD50 values. Azadirachtin considerably increased the toxicity of all insecticides in both adults and mature larvae after 72 hours exposure. The co-toxicity coefficient of all insecticides indicates synergistic action. The co-toxicity coefficient of azadirachtin indicates synergistic action when combined with deltamethrin and imidacloprid on adults in RFM test. The combination of deltamethrin and imidacloprid with azadirachtin was the most effective for controlling adults in residual film method (RFM). Deltamethrin+ azadirachtin was the best combination for controlling of mature larvae in both residual film method (RFM) and treated flour method (TFM). Imidacloprid+ azadirachtin combination was the best for controlling of adults in both residual film method (RFM) and treated flour method (TFM). Thiodicarb and imidacloprid was the most toxic at single action. Deltamethrin was less toxic at single action but when combined with azadirachtin then it was the most toxic on A. diaperinus.