Fusarium species associated with Euwallacea xanthopus in South Africa, including two novel species

Abstract

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are small wood-boring insects that live in an obligate symbiosis with fungi, which serve as their primary food source. Beetles residing in the genus Euwallacea have evolved a unique association with a clade of Fusarium that falls within the aptly named Ambrosia Fusarium Clade (AFC). The discovery of the invasive polyphagous shot hole borer, E. fornicatus, in South Africa, has heightened awareness of ambrosia beetles and their symbionts in the country. In this study, we investigated the Fusarium symbionts of three species of Euwallacea in South Africa, with a specific focus on those associated with E. xanthopus. Isolations of Fusarium strains from both living and dissected beetles yielded nearly 100 isolates. Using multigene phylogenetic analyses, these isolates were identified as six different Fusarium species. Fusarium hypothenemi and F. euwallaceae have previously been reported from South Africa. Fusarium pseudensiforme and Fusarium AF-6 are new records for the country. The remaining two species are new to science and are described here as F. rufum sp. nov. and F. floriferum sp. nov. Targeted fungal isolation from specific beetle body parts revealed that the AFC species collected were typically associated with the dissected beetle heads and helped us identify the likely nutritional symbiont of E. xanthopus. This study highlights the understudied diversity of fungal associates of ambrosia beetles present in South Africa.