Ambrosia Beetles

An ambrosia beetle, commonly known as Polyphagous Shot Hole Borer (PSHB) Euwallacea fornicatus (Coleoptera: Curculionidae: Scolytinae), is considered to be a pest, due to its ability to damage trees by acting as a vector for a pathogenic fungi. Fusarium euwallaceae, the fungal symbiont of the PSHB, is inoculated into the tree by the beetle. Eventually, the fungal symbiont prevents the transport of water and nutrients by invading the xylem, that leads to Fusarium dieback and the eventual death of the host tree. This pest-pathogen complex has emerged as an invasive pest in Israel and the United States of America (California), causing severe damage and significant economic losses to agricultural, ornamental and urban trees, especially to their avocado industries.

This pest-pathogen complex was detected in South Africa damaging Platanus x acerifolia (London Plane) trees in the National Botanical Gardens, KwaZulu-Natal. Recently, it was detected on a backyard tree and in a commercial avocado orchard. Control management strategies for this pest complex are limited due to inefficient trapping mechanisms, lack of biocontrol measures and inefficient fungicides. The use of resistant/tolerant trees could serve as a potential control strategy. Current research within the Avocado Research Programme (ARP) is therefore aimed at identifying Fusarium spp. isolates sampled from avocado trees to determine the extent of the threat to industry, after which the taxonomy of these isolates will be defined. We are also in the process of determining the threat on various, commonly growth avocado cultivars through the use of multiple pathogenicity trials.

*Read more about Ambrosia beetles and Fusarium dieback on our Fact sheet here.

ARP Team Members

Images from left to right: 1. Xylosandrus crassiusculus fungal symbiont Ambrosiella roeperi in culture. 2. Internal symptoms of PSHB infestation as beetles establish a network of galleries. 3. PSHB interception traps used in orchards.

New Publications

Magagula P, Swart V, Fourie A, Vermeulen A, Nelson JH, van Rooyen Z, van den Berg N. (2025) Avocado rhizosphere community profiling: white root rot and its impact on microbial composition. Frontiers in Microbiology 16 10.3389/fmicb.2025.1583797

van den Berg N, Magagula P, Backer R, Swart V. (2025) Towards developing an integrated approach for the treatment of white root rot in commercial avocado orchards. Phytoparasitica 53(32) 10.1007/s12600-025-01250-1

Harvey A, van den Berg N, Swart V. (2025) In silico characterisation of the avocado WAK/WAKL gene family with a focus on genes involved in defence against Phytophthora cinnamomi. Frontiers in Plant Science 15:1474781. 10.3389/fpls.2024.1474781

Harvey A, van den Berg N, Swart V. (2024) Describing and characterizing the WAK/WAKL gene family across plant species: a systematic review. Frontiers in Plant Science 15:1467148. 10.3389/fpls.2024.1467148

Joubert M, van den Berg N, Theron J, Swart V. (2024) Global transcriptomic analysis in avocado nursery trees reveals differential gene expression during asymptomatic infection by avocado sunblotch viroid (ASBVd). Virus Research 339:199263. 10.1016/j.virusres.2023.199263.

Anbu SP, Swart V, van den Berg N. (2023) Unmasking the invaders: NLR-mal function in plant defense. Frontiers in Plant Science 14:1307294. 10.3389/fpls.2023.1307294

Backer R, Naidoo S, van den Berg N. (2023) The expression of the NPR1-dependent defense response pathway genes in Persea americana (Mill.) following infection with Phytophthora cinnamomi. BMC Plant Biology 23(1):548. 10.1186/s12870-023-04541-z

Wingfield BD, Berger DK, Coetzee MPA, Duong TA, Martin A, Pham NQ, Van den Berg N, Wilken PM, Arun-Chinnappa KS, Barnes I, Buthelezi S, Dahanayaka BA, Durán A, Engelbrecht J, Feurtey A, Fourie A, Fourie G, Hartley J, Kabwe ENK, Maphosa M, Narh Mensah DL, Nsibo DL, Potgieter L, Poudel B, Stukenbrock EH, Thomas C, Vaghefi N, Welgemoed T, Wingfield MJ. (2022) IMA genome‑F17 Draft genome sequences of an Armillaria species from Zimbabwe, Ceratocystis colombiana, Elsinoë necatrix, Rosellinia necatrix, two genomes of Sclerotinia minor, short‑read genome assemblies and annotations of four Pyrenophora teres isolates from barley grass, and a long-read genome assembly of Cercospora zeina. 13:19. 10.1186/s43008-022-00104-3

Wienk R, Mostert‑O’Neill M, Abeysekara N, Manosalva P, Freeman B, van den Berg N. (2022) Genetic diversity, population structure and clonal verification in South African avocado cultivars using single nucleotide polymorphism (SNP) markers. Tree Genetics and Genomes 18(41) 10.1007/s11295-022-01573-8

Joubert M, van den Berg N, Theron J, Swart V. (2022) Transcriptomics Advancement in the Complex Response of Plants to Viroid Infection. International Journal of Molecular Sciences 23(7677) 10.3390/ijms23147677

Backer R, Engelbrecht J, van den Berg N. (2022) Differing Responses to Phytophthora cinnamomi Infection in Susceptible and Partially Resistant Persea americana (Mill.) Rootstocks: A Case for the Role of Receptor-Like Kinases and Apoplastic Proteases. Frontiers in Plant Science 13 10.3389/fpls.2022.928176

Kooverjee BB, Soma P, Neser FWC, Van der Nest MA, Scholtz MM. (2022) Selection Signatures in South African Nguni and Bonsmara Cattle Populations Reveal Genes Relating to Environmental Adaptation.. Frontiers in Genetics 13:909012. 10.3389/fgene.2022.909012

Hartley J, Engelbrecht J, Van den Berg N. (2022) Detection and prevalence of Rosellinia necatrix in South African avocado orchards. European Journal of Plant Pathology 10.1007/s10658-022-02532-8

Fick A, Swart V, Van den Berg N. (2022) The ups and downs of plant NLR expression during pathogen infection. Frontiers in Plant Science 13:921148. 10.3389/fpls.2022.921148

Midgley KA, van den Berg N, Swart V. (2022) Unraveling plant cell death during Phytophthora Infection. Microorganisms 10(6) 10.3390/microorganisms10061139

Miyambo TM, Backer R, Engelbrecht J, Joubert F, van der Merwe NA, van den Berg N. (2022) The Identification and Characterization of Endopolygalacturonases in a South African Isolate of Phytophthora cinnamomi. Microorganisms 10(1061) 10.3390/microorganisms10051061

Fick A, Swart V, Backer R, Bombarely A, Engelbrecht J, van den Berg N. (2022) Partially Resistant Avocado Rootstock Dusa® Shows Prolonged Upregulation of Nucleotide Binding-Leucine Rich Repeat Genes in Response to Phytophthora cinnamomi Infection. Frontiers in Plant Science 13:793644. 10.3389/fpls.2022.793644

Wingfield BD, De Vos L, Wilson AM, Duong AT, Vaghefi N, Botes A, Kharwar RN, Chand R, Poudel B, Aliyu H, Barbetti MJ, Chen S, de Maayer P, Liu F, Navathe S, Sinha S, Steenkamp ET, Suzuki H, Tshisekedi KA, van der Nest MA, Wingfield MJ. (2022) Draft genome assemblies of Fusarium marasasianum, Huntiella abstrusa, two Immersiporthe knoxdaviesiana isolates, Macrophomina pseudophaseolina, Macrophomina phaseolina, Naganishia randhawae, and Pseudocercospora cruenta. IMA Fungus 13(1):3. 10.1186/s43008-022-00089-z

Engelbrecht J, Duong TA, Paap T, Hulbert JM, Hanneman J, Van den Berg N. (2022) Population genetic analyses of Phytophthora cinnamomi reveals three lineages and movement between natural vegetation and avocado orchards in South Africa. 10.1094/PHYTO-10-21-0414-R

Kooverjee BB, Soma P, Neser FWC, Van der Nest MA, Scholtz MM. 2022. Copy number variation analysis in Nguni and Bonsmara crossbred cattle. In: Proceedings of 12th World Congress on Genetics Applied to Livestock Production (WCGALP). Veerkamp RF, de Haas Y. (eds). Wageningen Academic Publishers, pp 2187-2190.

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