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

Shaohui Wu,Jaime C Piñero,Michael D Toews,Muhammad Usman,David Ian Shapiro-Ilan,Waqas Wakil

doi:10.3390/microorganisms9081791

Abstract

Fruit flies including Bactrocera zonata and B. dorsalis (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 B. zonata and B. dorsalis. In virulence assays against third instars and adults, all 21 EPF isolates (Beauveria bassiana and Metarhizium anisopliae) tested were pathogenic and caused varying levels of mortality to the fruit flies. Based on the initial screening, four isolates (B. bassiana WG-21 and WG-18 and M. anisopliae WG-07 and WG-02) were selected for further study. The isolate WG-18 was the most virulent against larvae and adults of B. zonata and B. dorsalis 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 B. bassiana isolates WG-18 and WG-21 were the most virulent against multiple life stages of B. zonata and B. dorsalis, and also exerted the strongest sub-lethal effects.

Highlights

Fruit flies (Diptera: Tephritidae) are among the most economically important pest species in the world, attacking a wide range of fruits and fleshy vegetables throughout tropical and sub-tropical areas [1,2]
There was a significant effect of entomopathogenic fungi (EPF) isolates on larval mortality (B. zonata: F20, 125 = 242, p < 0.001; B. dorsalis: F20, 125 = 225, p < 0.001) and adult mortality (B. zonata: F20, 125 = 265, p < 0.001; B. dorsalis: F20, 125 = 217, p < 0.001)
The 21 EPF isolates tested showed varying levels of virulence, with mean mortality ranging from 2.5% to 88.2%

Summary

Introduction

Fruit flies (Diptera: Tephritidae) are among the most economically important pest species in the world, attacking a wide range of fruits and fleshy vegetables throughout tropical and sub-tropical areas [1,2]. Bactrocera Macquart is the most economically significant fruit fly genus with at least 50 species considered to be important pests, many of which are highly polyphagous [2]. Fruit flies cause direct damage to the fruit. Gravid females oviposit just under the fruit skin. The fruit rots and prematurely drops to the ground, thereby reducing yield [3,4]. Additional economic losses occur when importing countries prevent the introduction of commodities due to the presence of maggots inside the consignment. As a result, exporting countries lose their potential markets due to quarantine restrictions [5].

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