Microemulsion Formulations Of Rotenone And Their Effectiveness Against The Diamondback Moth (Lepidoptera: Yponomeutidae)

Oil-in-water (O/W) microemulsions were prepared by the titration method through phase diagram study. The mixture consisted of surfactant, oil (as carrier), and water. The surfactants were Agnique PG 8107-U, Agnique PG 9116, and Tween 20 while the oils were Agnique BL 7001, Agnique BL 7002, and xylene. The potential of plant-derived insecticide rotenone (Derris elliptica) microemulsion formulations and their effectiveness against crucifer insect pest namely diamondback moth, Plutella xylostella were investigated in laboratory. The objectives of this study were, therefore, to formulate rotenone as microemulsion formulations through phase diagram study, to characterize the formulations, and to determine their LC50 on diamondback moth by bioassay study.Twelve phase diagrams of ternary systems were constructed and isotropic region were established. The systems having wider isotropic region were selected and they were Agnique 8107-U/Agnique BL 7001/water, Agnique 9116/Agnique BL 7001/water, Tween 20/Agnique BL 7001/water, Agnique PG 8107-U/Agnique BL 7002/water, Tween 20/Agnique BL 7002/water and Tween 20/Edenor ME/water systems. From these phase diagrams, 13 microemulsion solutions were derived. These microemulsion solutions were further evaluated for miscibility, surface tension, and particle size analysis. The phase diagram systems containing Tween 20 as the surfactant showed the greater ability to produce a wider isotropic (microemulsion) region compared to others. The miscibility test showed all surfactants mixed readily with water. In interaction with the all oil phases, Tween 20 showed better miscibility compared with Agnique PG 8107-U and Agnique PG 9116 which produce double layers isotropic emulsion in absence of water. The width of isotropic/transparent region in phase diagrams constructed measured in decreasing order were; Tween 20/Agnique BL 7002/ water > Tween 20/Agnique BL 7001/water > Tween 20/Edenor ME/water > Agnique PG 9116/Agnique BL 7001/water > Agnique PG 8107-U/Agnique BL 7001/water > Agnique PG 8107-U/Agnique BL 7002/water > Tween 20/xylene/water > Agnique PG 9116/Agnique BL 7002/water > Agnique PG 9116/xylene/water > Agnique PG 8107-U/xylene/water > Agnique PG 8107-U/Edenor ME/water > Agnique PG 9116/Edenor ME/water.Three phase diagram systems representing the best microemulsifiable characterization properties and solubility with rotenone were Tween 20/Agnique BL 7001/water, Tween 20/Agnique BL 7002/water and Tween 20/Edenor ME/water systems. Six points in the isotropic regions of the selected phase diagrams were utilized to prepare the microemulsion and coded as M1 to M13. The microemulsions were then subjected to the determination of their surface tensions and particle sizes. The surface tension values of the selected microemulsions were low and their values in decreasing order were; M9 (27.3 mN/m) > M13 (26.9 mN/m) > M2 (26.8 mN/m) > M4 (26.4 mN/m) > M11 (22.8 mN/m) > M7 (22.7 mN/m). The particle size of the microemulsion in decreasing order were; M4 (207.57 nm) > M13 (83.31 nm) > M2 (68.7 nm) > M11 (49.03 nm) > M9 (35.86 nm) > M7 (20.63 nm). The selected microemusions were used to prepare the rotenone microemulsion formulations. The formulations were then evaluated for their toxicity in comparison with the standard commercial EC formulation (Saphyr®) against the early third instar larvae of the diamondback moth by leaf-dipped bioassay in the laboratory. The mortality of the larvae was recorded at 72 and 96 hours following treatment and data were subjected to the Probit analysis to establish the LC50 and LC95. Based on LC50 values, the toxicity of formulations for 72 hours after treatment in decreasing order were M11 (204.82 ppm) > M7 (139.71 ppm) > M13 (129.89 ppm) > M4 (122.8 ppm) > M2 (116.94 ppm) > M9 (96.09 ppm) > Saphyr® (96.05 ppm) while for 96 hours after treatment, the toxicity in decreasing order were M11 (166.63 ppm) > M7 (119.58 ppm) > M13 (105.82 ppm) > M2 (105.22 ppm) > M4 (97.67 ppm) > M9 (87.22 ppm) > Saphyr® (76.86 ppm). The toxicity study indicated that the rotenone microemulsion formulations especially M9 were comparable to commercial rotenone, Saphyr®.

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