Evaluation of Locally Isolated Entomopathogenic Fungi against Multiple Life Stages of <i>Bactrocera zonata</i> and <i>Bactrocera dorsalis</i> (Diptera: Tephritidae): Laboratory and Field Study

• Main Authors: Muhammad Usman, Waqas Wakil, Jaime C. Piñero, Shaohui Wu, Michael D. Toews, David Ian Shapiro-Ilan
• Format: Article
• Language: English
• Published: MDPI AG 2021-08-01
• Series: Microorganisms
• Subjects: entomopathogenic fungi; horizontal transmission; host development; biological control
• Online Access: https://www.mdpi.com/2076-2607/9/8/1791

Fruit flies including <i>Bactrocera zonata</i> and <i>B. dorsalis</i> (Diptera: Tephritidae) are considered major pests of orchard systems in Pakistan. This study evaluated the laboratory virulence, sub-lethal effects, horizontal transmission, greenhouse, and field-cage efficacy of locally isolated entomopathogenic fungi (EPF) against <i>B. zonata</i> and <i>B. dorsalis</i>. In virulence assays against third instars and adults, all 21 EPF isolates (<i>Beauveria bassiana</i> and <i>Metarhizium anisopliae</i>) tested were pathogenic and caused varying levels of mortality to the fruit flies. Based on the initial screening, four isolates (<i>B. bassiana</i> WG-21 and WG-18 and <i>M. anisopliae</i> WG-07 and WG-02) were selected for further study. The isolate WG-18 was the most virulent against larvae and adults of <i>B. zonata</i> and <i>B. dorsalis</i> followed by WG-21, WG-02, and WG-07. In both species, adults were more susceptible than larvae to all isolates, and pupae were the least susceptible. Isolates WG-18 and WG-21 strongly decreased female fecundity and fertility, the highest adult and larval mortality, and longest developmental time of larvae and pupae. Fungal conidia were disseminated passively from infected to healthy adults and induced significant mortality, particularly from infected males to non-infected females. In greenhouse and field-cage experiments, WG-18 and WG-21 were the most effective isolates in reducing adult emergence when applied to larvae and pupae of both fruit fly species. Our results indicate that <i>B. bassiana</i> isolates WG-18 and WG-21 were the most virulent against multiple life stages of <i>B. zonata</i> and <i>B. dorsalis</i>, and also exerted the strongest sub-lethal effects.