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Galls are abnormal growths on a plant that can have various causes, including viruses, nematodes, bacteria, fungi, mites and insects. Aphids, flies and wasps are some of the insects known to cause galls. Generally plants can tolerate galls with no obvious injury. However, a very high incidence of galls can damage and even kills plants.

Gall formers on eucalypts

The Eucalyptus gall wasp (Leptocybe invasa) is currently the only gall forming insect in South Africa which is considered a serious pest of plantation forest trees. This insect, which infests Eucalyptus, was accidentally introduced from Australia. It was first detected in South Africa in 2007 (and only in 2009 in forestry areas). The Eucalyptus gall wasp causes galls on the stems, petioles and midrib of leaves. Damage by this insect is particularly severe on younger trees, where the majority of leaves can have galls, resulting in severe leaf drop. In such cases, stunting of growth and possibly tree death can occur. The adult wasp is minute (about 1.4 mm), but the galls, which often contain multiple eggs of the Eucalyptus gall wasp, are easily visible. Severely infested trees have a gnarled appearance.

New Publications

Coelho MA, David-Palma M, Marincowitz S, Aylward J, Pham NQ, Yurkov AM, Wingfield BD, Wingfield MJ, Sheng S, Heitman J. (2025) The complex evolution and genomic dynamics of mating-type loci in Cryptococcus and Kwoniella. PLoS Biology 23:e3003417. 10.1371/journal.pbio.3003417
Visagie CM, Houbraken J, Overy DP, Sklenář F, Bensch K, Frisvad JC, Mack J, Perrone G, Samson RA, van Vuuren NI, Yilmaz N, Hubka V. (2025) From chaos to tranquillity: a modern approach to the identification, nomenclature and phylogeny of Aspergillus, Penicillium and other Eurotiales, including an updated accepted species list. Studies in Mycology 112:117–260. 10.3114/sim.2025.112.04
Joubert M, van den Berg N, Theron J, Swart V. (2025) Small RNAs derived from avocado sunblotch viroid and their association with bleaching symptoms: implications for pathogenesis in avocado sunblotch disease. Archives of Virology 170(10):205. 10.1007/s00705-025-06360-z PDF
Mavima L, Steenkamp ET, Beukes CW, Palmer M, De Meyer SE, James EK, Venter SN, Coetzee MPA. (2025) Estimated timeline for the evolution of symbiotic nitrogen fixing Paraburkholderia. Molecular Phylogenetics and Evolution 213:108447. 10.1016/j.ympev.2025.108447
Pham NQ, Liu FF, Duong TA, Wingfield BD, Chen SF, Wingfield MJ. (2025) Genetic diversity of Calonectria reteaudii isolates from infected Eucalyptus leaves and associated soils indicates a phyllosphere origin of the pathogen. Forest Pathology 55:e70037. 10.1111/efp.70037