Ambrosia beetle and Fusarium wilt

from: Fact Sheet (Updated April 2018) - https://www.fabinet.up.ac.za/images/groups/ARP/ARP-Website-Fusarium-dieback-Fact-sheet-March-2018.pdf
(*by Noëlani van den Berg, Avocado Research Programme (FABI), University of Pretoria)

Euwallacea cf. fornicatus (Polyphagous Shothole Borer) is an Ambrosia Beetle native to Asia that has a symbiotic relationship with species of Fusarium fungus - including the pathogen Fusarium euwallaceae.
This fungus is responsible for Fusarium Dieback in Israel, California and Florida

The beetle carries spores within a special fungal pouch in its mandibles. Adult females burrow into trees and deposit the fungi to establish brood galleries. The fungus proliferates on the gallery walls and is grazed by both larvae and adult beetles. The fungal threads invade the wood tissues, causing necrosis of the cambium, resulting in dieback and death of some plants.
Some 200 trees are attacked by the beetle and fungus, although only about half support fungal growth, and only about a third of those supporting the fungus can be used by the beetles to reproduce.

Symptoms vary a lot, depending on hosts and levels of infection. The beetle itself is very small and hard to see. Their galleries penetrate 10-40 mm into the wood, and usually have several exit holes (with "sugar volcanos") on infested trees. Females are black and 1.8-2.5 mm long and males are brown and 1.5 mm long.

Hosts in South Africa include
Avocado (Persea americana),
Box Elder (Acer negundo),
Castor Bean (Ricinus communis),
Oak (Quercus spp.),
Citrus (Citrus spp.),
Tea (Camelia sinensis) and
London Plane (Platanus x acerifolia).

Less suitable hosts include Litchi, Mango and Cacao.
Affected fruits include:
Macadamia Nut (Macadamia integrifolia),
Pecan (Carya illinoinensis),
Peach (Prunus persica) and
Grape (Vitis vinifera)

Native species affected include:
Cabbage Tree (Cussonia spicata;
Common Calpurnia (Calpurnia aurea),
Monkey Plum (Diospyros lycioides),
Dwarf Coraltree ( Erythrina humeana)
Common Coraltree (Erythrina lysistemon),
Short Boerbean (Schotia brachypetala),
Honeyflower (Melianthus major),
Red Alder (Cunonia capensi),
Forest Alder (Nuxia floribunda) and
Red Orchid Bush (Bauhinia galpinii).

Please report any instances on iNaturalist.

Further reading:
https://www.fabinet.up.ac.za/publication/pdfs/3351-paap_et_al_2018_austr_pl_path.pdf
The polyphagous shot hole borer (PSHB) and its fungal symbiont. Fusarium euwallaceae: a new invasion in South Africa
Trudy Paap & Z. W. de Beer & D. Migliorini & W. J. Nel & M. J. Wingfield
Australasian Plant Pathology https://doi.org/10.1007/s13313-018-0545-0

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Posted on 27 July, 2018 21:34 by tonyrebelo