A doctoral study in the Forestry and Agricultural Biotechnology Institute confirms for the first time the presence of Xylosandrus crassiusculus, a polyphagous ambrosia beetle and its fungal symbiont, Ambroseilla roeperi, in three provinces in South Africa. The authors warn that this beetle species could be a threat to native and plantation trees. Results from this work appear in Zootaxa.  

A South East Asian ambrosia beetle, Xylosandrus crassiusculus has been introduced to Europe, the Americas and several African countries, “but only as far south as Tanzania” in Africa, the authors report. The researchers warn that because of its polyphagous and haplo-diploid nature, X. crassiusculus could be difficult to control.

“These facts are particularly relevant in South Africa, where X. crassiusculus is already widespread and has now been found infesting avocado and macadamia trees, both important to local agriculture. However, it must be noted that both tree species were stressed at the time of the infestation due to environmental factors, so the effect that X. crassiusculus might have on these industries remains unclear,” write the researchers.

These outcomes are part of a PhD study by Wilma Nel investigating the diversity of ambrosia beetles and their fungal symbionts in natural forests in South Africa. The discovery of Euwallacea fornicatus, a destructive ambrosia beetle also known as the polyphagous shothole borer (PSHB) in South Africa in 2017, resulted in renewed bark and ambrosia beetle research in the country. 

“Concern regarding the PSHB has resulted in many samples of scolytine-infested wood being examined, including avocado (Persea americana) and macadamia (Macadamia integrifolia x M. tetraphylla) logs, but much of the material was infested with species other than PSHB” write the authors.

This study included samples collected from avocado in the Northern Cape and Limpopo provinces as well as from macadamia in KwaZulu-Natal. Out of these samples, the researchers came across an unidentified ambrosia beetle species. Using morphological characters and COI sequence data, the researchers identified the ambrosia beetle as X. crassiusculus representing “two distinct haplotypes.”

Maximum likelihood phylogenetic analyses of COI sequence data grouped X. crassiusculus specimens from Kwazulu-Natal and the Northern Cape with specimens from geographically distant locations including Panama, Thailand, and Madagascar. The specimens from Limpopo grouped with specimens from Argentina, France, and the United States, wrote the authors.

Ambrosia beetles are known to associate with fungi that are agents of various diseases and sapstain of lumber. In this study, “[t]he fungal symbiont, Ambrosiella roeperi, was isolated and identified using DNA sequencing and morphological characterization,” write the authors.

“Xylosandrus crassiusculushas been present on mainland Africa for many years but the present study represents the first record of both the insect and its fungal symbiont A. roeperi in South Africa. Its presence infesting important agronomic tree crops such as macadamia and avocado suggests that it requires further study,” conclude the authors.

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