Temperature effects on the virulence of entomopathogenic fungi to manage the bronze bug Thaumastocoris peregrinus (Hemiptera: Thaumastocoridae)

Abstract

Abstract Thaumastocoris peregrinus Carpintero & Dellapé (Hemiptera: Thaumastocoridae), a sap-sucking pest native to Australia, has severely impacted eucalyptus plantations in Brazil since 2008. Due to environmental concerns and resistance risks, chemical control is restricted in forest systems, prompting the search for sustainable alternatives. Entomopathogenic fungi (EPF) offer promising potential for integrated pest management (IPM) strategies. This study evaluated the virulence and thermal tolerance of EPF isolates against T. peregrinus through a multi-phase bioassay. Initially, eleven fungal isolates were screened for pathogenicity against adults. Based on mortality rates, three isolates Beauveria bassiana (IBCB227), Metarhizium anisopliae (IBCB425), and Cordyceps farinosa (IBCB220) were selected for further testing at constant temperatures (20, 25, and 30 °C). Subsequently, lethal concentration (LC50) and lethal time (LT50) were determined for the two most virulent isolates (IBCB227 and IBCB425) in both nymphs and adults. IBCB425 demonstrated high efficacy across all temperatures, while IBCB227 and IBCB220 were less effective at 20 °C. LC50 values were 1.10 × 107 and 2.10 × 106 conidia/mL for IBCB227 and IBCB425, respectively, based on mortality recorded six days post-application. LT50 was calculated using the highest concentration (1.0 × 108 conidia/mL), with IBCB425 inducing faster mortality (3.75 days) than IBCB227 (4.43 days). Post-mortem sporulation confirmed fungal infection in >90% of cadavers. These findings highlight the virulence and temperature resilience of M. anisopliae IBCB425 and B. bassiana IBCB227, supporting their potential as effective biological control agents for T. peregrinus in eucalyptus plantations under variable environmental conditions.