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

## TL;DR

This study introduces an eco-friendly pesticide made from soy sauce waste and a fungus that effectively controls citrus pests, offering a sustainable alternative to chemicals.

## Contribution

A new plant spray oil and its synergistic mixture with Metarhizium anisopliae provide effective, eco-friendly pest control for Diaphorina citri.

## Key findings

- The plant spray oil and M. anisopliae mixture achieved over 80% control efficacy against D. citri within 6 days.
- The optimal 5:5 mixing ratio showed the strongest synergistic effect in pest control.
- The treatment reached 96.28% efficacy by day 8, comparable to chemical control methods.

## Abstract

Diaphorina citri, the natural transmission vector of the destructive disease Huanglongbing, is the most important pest in citrus production. This research provides a method for the eco-friendly control of D. citri. A new plant spray oil, based on plant glycerides extracted from soy sauce waste residue, was developed into an environmentally friendly pesticide, which can quickly and effectively control D. citri. When mixed with Metarhizium anisopliae, it had a significant synergistic effect. Field application showed that the control efficacy of the plant spray oil and M. anisopliae mixture on D. citri was equivalent to that of chemical control, presenting a viable alternative for eco-friendly pest management. This study provides a scientific basis for effectively controlling D. citri and preventing the further spread of Huanglongbing in the field.

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.