Evaluation of commercial formulations of entomopathogenic fungi to manage the redbay ambrosia beetle, vector of laurel wilt, a lethal disease affecting avocados in Florida

The redbay ambrosia beetle (RAB), Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae) vectors the fungal pathogen, Raffaelea lauricola, which causes laurel wilt, a lethal disease of trees in the family Lauraceae, including the most commercially important crop in this family, avocado, Persea americana. The objective of this study was to determine the susceptibility of RAB to infection and subsequent death by exposure to four commercial strains of entomopathogenic fungi. RAB females were exposed separately to two strains of Isaria fumosorosea, Ifr 3581 and PFR 97^® 20% WDG, one strain of Metarhizium brunneum (Met F52^® ES), and one strain of Beauveria bassiana (BotaniGard^® ES). RAB females were dipped in fungal spore suspensions and the time to kill 50% of the beetles (LT₅₀) was determined. Contact with all of the biopesticides resulted in death of all RAB females within a few days. LT₅₀ of RAB females exposed to the different entomopathogenic fungi ranged from 2.92 days (BotaniGard) to 4.75 days (PFR). BotaniGard and Met F52 killed RAB females the fastest, followed by Ifr 3581 and PFR. No significant differences were observed in the mortality of beetles that were dipped in fungal spore suspensions and then offered avocado logs as a substrate, compared with beetles that were allowed to walk on logs previously treated with the different fungi. Beetles were able to bore into the logs and construct galleries but were found dead inside the galleries a few days after exposure to the entomopathogens. Additional research is needed to determine the effectiveness of entomopathogenic fungi to control RAB infestations under field conditions.