Evaluation of Synthetic and Natural Insecticides for the Management of Insect Pest Control of Eggplant ( Solanum Melongena L.) and Pesticide Residue Dissipation Pattern

Abstract

Eggplant shoot and fruit borer (ESFB), Leucinodes orbonalis G. is a key pest of eggplant, Solanum melongena L. Organophosphates (OP) having high toxicity and persistence are used to control the pests in many developing countries, despite availability of new insecticides with better qualities. Field evaluation of thiacloprid and indoxacarb were carried out against ESFB, with an OP insecticide, methyl parathion. Two Bacillus thuriegensis (Bt) based formulations namely Biolep and PUSA Bt and two azadirachtin formulations namely Neem Seed Kernal Extract (NSKE) and Nimbo Bas were also evaluated against ESFB for the management of the pest. HPLC and GC methods for the estimation of indoxacarb, thiacloprid and methyl parathion from the fruits were developed and their dissipation patterns and safety parameters were compared. For indoxacarb, the method involving Florisil gave highest recovery (88%) whereas average recoveries of other methods varied from 59% to 82%. The mean initial deposits of indoxacarb on fruits were 2.60 mg/kg to 3.64 mg/kg and 2.63 mg/kg to 3.68 mg/kg from 75 and 150 g·ai/ha treatments from two-year field studies. The half-life of indoxacarb was 3.0 d - 3.8 d from both years. The Theoretical Maximum Daily Intake (TMDI) was found to be 0.446 mg/person/day to 0.643 mg/person/day for day-1 residues which is in par with the Maximum Permissible Intake (MPI) of 0.6 mg/person/day. The TMDI from 3 d residues was found to be less than the MPI calculated with the data of 3 d residues which ensures better margin of safety. For thiacloprid, the method involving Florisil gave highest recovery (89%). The mean initial deposits of thiacloprid on fruits were 3.39 to 5.40 mg/kg and 3.40 to 5.39 mg/kg from 30 and 60 g·ai/ha treatments from both years. The half-life values were determined to be 11.1 and 11.6 d for both years. The TMDI from maximum residues observed for first day for both the treatments during first year trials was found to be 0.682 to 1.098 mg person/day, which was higher than the MPI of 0.72 mg/person/day, which proved that the application is toxic to humans. Thiacloprid at the experimented doses (30 and 60 g·ai/ha) was found not effective to manage ESFB and was not safe for human consumption after a waiting period of 3 days. For methyl parathion, the method involving Florisil gave highest average recovery (89%). The initial residues on fruits from recommended dose declined from 3.60 to 3.12 mg/kg in one day and 0.27 mg/kg in twentyfive days from 100 g·ai/ha. Similar pattern was observed with higher dose also. The dissipation rate constants were 0.123 and 0.140 for 100 and 200 g·ai/ha treatments, respectively. The half life values ranged from 6.0 to 7.4 days. Using dose (100 g·ai/ha), the residues reached safe level only after 20 days. A minimum gap of 20 days after the last application of the insecticide to the harvest is impractical for this crop. The efficacy of methyl parathion against ESFB was good at lower dose, but due to its toxic residue profile there is a high health risk. Biolep at both doses were not effective against ESFB, however PUSA Bt gave better control against ESFB at similar dose. NSKE was found effective against ESFB, however NimboBas found to be non-effective against ESFB.