Evaluation of Laboratory Toxicities and Field Application of Plant Spray Oil and Its Mixture with Metarhizium anisopliae Against Diaphorina citri Kuwayama (Hemiptera: Liviidae)

Abstract

Overusing chemicals to manage Diaphorina citri has created insecticide resistance and negative impacts on the natural ecosystem. This has prompted the need to develop new methods of control. In the present study, we evaluated the toxicity of plant spray oil, Metarhizium anisopliae, and their combined formulations against D. citri adults through laboratory bioassays. We tested varying concentrations and application doses of the individual agents and their mixtures to determine synergistic effects. The optimal mixing ratio of M. anisopliae and plant spray oil for enhanced pest control efficacy was also identified. The results showed that the control effect of plant spray oil and M. anisopliae on D. citri became more pronounced as the concentration increased. When the two were mixed in different proportions, the synergistic effect of plant spray oil was the strongest when the mixing ratio was 5:5. Field trials demonstrated that a combined treatment of plant spray oil emulsion (9.10 g/L) and M. anisopliae (1 × 10⁸ spores/mL) achieved over 80% relative control efficacy against adult D. citri by the 6th day post-treatment. Its efficacy further increased to 96.28% by the 8th day, demonstrating its potential to replace chemical control methods. This study provides a practical example for exploring biopesticides and leveraging the synergistic effects of biogenic pesticides in preventing and controlling pests.

Keywords: Diaphorina citri; Metarhizium anisopliae; chemical substitute; mix proportion; plant spray oil; synergistic effect; virulence.

Figure 1

Comparison of time–mortality relationship for M. anisopliae used on D. citri adults inoculated with spores at varied concentrations. Spore suspensions were prepared in 0.02% Tween-80 solution at concentrations of 2.5 × 10⁷, 5 × 10⁷, 1 × 10⁸, 2 × 10⁸, and 3 × 10⁸ spores/mL, with the 0.02% Tween-80 solution as the control.

Figure 2

Synergistic effect of plant spray oil and M. anisopliae on adults of D. citri according to interactive determination method.

Figure 3

Field control efficacy of D. citri with different treatments in the field. The experimental data were analyzed using one-way ANOVA, and Duncan’s new multiple range test was employed to test the differences among treatments. Different letters indicate significant differences (p < 0.05). Error bars represent the standard error of the mean.