# Synergistic Effects of Beauveria bassiana and Insecticides for Integrated Management of Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)

## TL;DR

This study explores combining a fungus with a low dose of insecticide to control the oriental fruit fly, showing potential for reducing chemical use and environmental impact.

## Contribution

The study identifies emamectin benzoate as compatible with Beauveria bassiana, demonstrating synergistic effects for pest control.

## Key findings

- Emamectin benzoate had the least inhibitory effect on Beauveria bassiana spore germination and mycelial growth.
- Combining Beauveria bassiana with emamectin benzoate showed synergistic effects against Bactrocera dorsalis adults in lab tests.
- Greenhouse trials showed the combined treatment reduced adult populations and pupal emergence rates more than individual treatments.

## Abstract

Bactrocera dorsalis (Hendel) (Diptera: Tephritidae), commonly known as the oriental fruit fly, is a highly invasive and economically significant pest with a global impact. Current control strategies for B. dorsalis are largely dependent on chemical insecticide. However, the prolonged and widespread use of these chemicals has raised several concerns, such as resistance. In this study, integrating biological control agents with lower doses of chemical insecticides can address these limitations to some extent, but the compatibility of fungal agents with insecticides is a critical consideration. In this study we evaluated the biocompatibility of six commonly used insecticides with B. bassiana Bb-33, assessed the synergistic potential of compatible insecticide–fungus combinations against B. dorsalis under laboratory conditions, and investigated the efficacy of the most promising combination against B. dorsalis adults and pupae in greenhouse trials. We found that emamectin benzoate exhibited the lowest inhibition of B. bassiana spore germination and mycelial growth across different concentrations. Moreover, combination treatments of B. bassiana Bb-33 with emamectin benzoate demonstrated synergistic effects against B. dorsalis adults in laboratory bioassays. Greenhouse trials revealed that the combined treatment significantly reduced B. dorsalis adult populations and pupal emergence rates compared to individual treatments.

Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) is a significant agricultural pest that causes substantial economic losses globally. While chemical insecticides are commonly used for its management, increasing resistance and environmental concerns underscore the need for alternative control strategies. This study evaluated the potential of integrating the entomopathogenic fungus Beauveria bassiana strain Bb-33 (Hypocreales: Clavicipitaceae) with reduced doses of chemical insecticides for sustainable B. dorsalis management. The compatibility of B. bassiana Bb-33 with six commonly used insecticides—spinosad, emamectin benzoate, avermectin, thiamethoxam, beta-cypermethrin, and imidacloprid—was assessed. Among them, emamectin benzoate exhibited the least inhibitory effects on spore germination, mycelial growth, and sporulation of B. bassiana. Laboratory bioassays demonstrated synergistic interactions between B. bassiana Bb-33 and emamectin benzoate, particularly when the ratio of emamectin benzoate to B. bassiana exceeded 4:1, as indicated by co-toxicity coefficients greater than 100. However, greenhouse trials revealed that the combined formulation had lower efficacy in reducing B. dorsalis adult populations and pupal emergence rates compared to emamectin benzoate alone, though it was more effective than B. bassiana Bb-33 applied independently. Importantly, this composite formula reduces pesticide usage, which highlights its potential to mitigate environmental impacts. This study underscores the promise of integrating B. bassiana Bb-33 with reduced doses of emamectin benzoate as a viable strategy for managing B. dorsalis. Despite its current limitations in greenhouse trials, further optimization of formulation stability and application methods could enhance its field performance, offering an effective and environmentally friendly alternative to conventional chemical control methods.