Preferred name: Euwallacea fornicatus sensu stricto
Authority: (Eichhoff)
Taxonomic position: Animalia: Arthropoda: Hexapoda: Insecta: Coleoptera: Curculionidae: Scolytinae
Other scientific names: Euwallacea whitfordiodendrus (Schedl), Xyleborus fornicatus Eichhoff, Xyleborus tapatapaoensis Schedl
Common names in English: polyphagous shot-hole borer
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Notes on taxonomy and nomenclature EPPO Code: EUWAWH

The Euwallacea fornicatus species complex has a broad host range. Gomez et al. (2019) updated the list of hosts to 412 plant species in 75 families; 109 are reported as breeding hosts, 95 are commercial timber tree species and 43 are species used for fruit production. Recently, after the report of E. fornicatus in South America, new additional hosts were recorded (Ceriani-Nakamurakare et al., 2023). In the United States (California), the beetles were found on more than 200 hosts, though only 19 of these were shown to be reproductive hosts (Eskalen et al., 2013).

Host list: Acacia auriculiformis, Acacia floribunda, Acacia longifolia, Acacia mangium, Acacia mearnsii, Acacia melanoxylon, Acacia saligna, Acacia stenophylla, Acacia victoriae, Acaciella glauca, Acer buergerianum, Acer campestre, Acer caudatifolium, Acer davidii, Acer japonicum, Acer macrophyllum, Acer negundo, Acer obtusifolium, Acer palmatum, Acer paxii, Acer pectinatum, Acer pictum subsp. mono, Acer pseudoplatanus, Acer saccharinum, Acer x freemanii, Adansonia digitata, Afrocarpus falcatus, Afrocarpus gracilior, Afzelia quanzensis, Aglaia odorata, Ailanthus altissima, Alangium chinense, Albizia adianthifolia, Albizia julibrissin, Albizia kalkora, Albizia lebbeck, Albizia sp., Alectryon excelsus, Alnus cordata, Alnus glutinosa, Alnus incana, Alnus rhombifolia, Aloysia virgata, Anisodontea scabrosa, Arbutus unedo, Archontophoenix alexandrae, Bambusa sp., Banksia saxicola, Bauhinia galpinii, Bauhinia petersiana, Bauhinia purpurea, Bauhinia variegata, Beilschmiedia miersii, Betula pendula, Bischofia javanica, Bocconia arborea, Bombax ceiba, Bougainvillea sp., Brachychiton acerifolius, Brachychiton australis, Brachychiton bidwillii, Brachychiton discolor, Brachychiton diversifolius, Brachychiton populneus, Brachychiton rupestris, Brachylaena discolor, Brahea armata, Broussonetia papyrifera, Buddleia saligna, Bunchosia armeniaca, Bursera hindsiana, Butia capitata, Caesalpinia mexicana, Callerya sp., Calliandra surinamensis, Callistemon salignus, Calodendrum capense, Calpurnia aurea, Camellia chrysanthoides, Camellia drupifera, Camellia grijsii, Camellia hiemalis, Camellia indochinensis, Camellia japonica, Camellia reticulata, Camellia rosiflora, Camellia semiserrata, Camellia x williamsii, Camptotheca acuminata, Carya illinoinensis, Cascabela thevetioides, Cassia brewsteri, Cassia leptophylla, Castanospermum australe, Casuarina cunninghamiana, Catalpa speciosa, Ceanothus caeruleus, Cedrus atlantica, Ceiba pentandra, Celtis africana, Celtis australis, Celtis bungeana, Celtis laevigata, Cercis chinensis, Cercis siliquastrum, Cestrum sp., Chamaedorea elegans, Chionanthus retusus, Chiranthodendron pentadactylon, Chorisia speciosa, Cinnamomum camphora, Cinnamomum glanduliferum, Cinnamomum tenuifolium, Citharexylum montevidense, Citrus x aurantium var. sinensis, Citrus x limon, Cleyera japonica, Cocculus laurifolius, Cocculus orbiculatus, Colletia paradoxa, Combretum erythrophyllum, Combretum kraussii, Commiphora harveyi, Cordia caffra, Cornus controversa, Cornus drummondii, Cornus florida, Corylus colurna, Corymbia ficifolia, Crinodendron patagua, Cunninghamella sp., Cunonia capensis, Cupaniopsis anacardioides, Cussonia spicata, Dahlstedtia pinnata, Dalbergia delavayi, Dalbergia sissoo, Davidia involucrata, Desmodium elegans, Diospyros dichrophylla, Diospyros glabra, Diospyros kaki, Diospyros lycioides, Diospyros whyteana, Diploglottis australis, Dombeya cacuminum, Dombeya rotundifolia, Dovyalis caffra, Dracaena draco, Ebenopsis ebano, Ehretia latifolia, Ekebergia capensis, Elaeocarpus decipiens, Enterolobium contortisiliquum, Eriobotrya japonica, Erythrina americana, Erythrina caffra, Erythrina chiriquensis, Erythrina corallodendron, Erythrina crista-galli, Erythrina falcata, Erythrina flabelliformis, Erythrina folkersii, Erythrina humeana, Erythrina livingstoniana, Erythrina lysistemon, Erythrina macrophylla, Erythrina variegata, Erythrina x bidwillii, Erythrina x sykesii, Eucalyptus camaldulensis, Eucalyptus cinerea, Eucalyptus froggattii, Eucalyptus kitsoniana, Eucalyptus perriniana, Eucalyptus polyanthemos, Eucalyptus torquata, Fagus crenata, Fagus sylvatica, Faidherbia albida, Fatsia japonica, Ficus altissima, Ficus benjamina, Ficus carica, Ficus macrophylla, Ficus maxima, Ficus natalensis, Ficus obliqua, Ficus platypoda, Ficus rubiginosa, Ficus sur, Firmiana simplex, Frangula californica, Fraxinus americana, Fraxinus excelsior, Fraxinus griffithii, Fraxinus sp., Fraxinus uhdei, Fraxinus velutina, Geijera parviflora, Gleditsia japonica, Gleditsia triacanthos, Grewia occidentalis, Gymnosporia buxifolia, Hakea salicifolia, Halleria lucida, Handroanthus impetiginosus, Harpephyllum caffrum, Harpullia arborea, Harpullia pendula, Hauya elegans subsp. cornuta, Heliocarpus donnellsmithii, Heteropterys purpurea, Hibiscus rosa-sinensis, Hovenia dulcis, Howea forsteriana, Hymenosporum flavum, Ilex aquifolium, Ilex cornuta, Ilex latifolia, Ilex mitis, Inga feuillei, Inga insignis, Inga sp., Inga uruguensis, Inga vera, Jacaranda cuspidifolia, Jacaranda mimosifolia, Jatropha cinerea, Jatropha mcvaughii, Juglans californica, Juglans mandshurica, Juglans nigra, Juglans regia, Juniperus chinensis, Juniperus virginiana, Kiggelaria africana, Koelreuteria bipinnata, Koelreuteria elegans, Leonotis leonurus, Liquidambar formosana, Liquidambar styraciflua, Liriodendron tulipifera, Livistona chinensis, Lonchocarpus nitidus, Luehea divaricata, Lysiphyllum carronii, Macadamia integrifolia, Machilus thunbergii, Magnolia campbellii, Magnolia compressa, Magnolia cylindrica, Magnolia delavayi, Magnolia denudata, Magnolia doltsopa, Magnolia foveolata, Magnolia grandiflora, Magnolia grandis, Magnolia guatemalensis, Magnolia hodgsonii, Magnolia liliiflora, Magnolia pacifica, Magnolia sargentiana, Magnolia sharpii, Magnolia sprengeri, Magnolia tamaulipana, Magnolia virginiana, Magnolia x brooklynensis, Magnolia x loebneri, Magnolia x soulangeana, Magnolia x veitchii, Magnolia yunnanensis, Malus domestica, Malus floribunda, Malus sylvestris, Manihot esculenta, Melaleuca viminalis, Melia azedarach, Melianthus major, Metasequoia glyptostroboides, Mezoneuron kauaiense, Milicia excelsa, Moringa sp., Morus alba, Morus nigra, Myrsine melanophloeos, Neltuma articulata, Neltuma glandulosa, Neolitsea sericea, Nuxia floribunda, Ochroma pyramidale, Olea europaea subsp. africana, Olea europaea, Olinia ventosa, Olneya tesota, Osmanthus fragrans, Osteospermum moniliferum, Pararchidendron pruinosum, Parasenegalia visco, Parkinsonia aculeata, Parkinsonia florida, Parkinsonia x sonorae, Peltophorum africanum, Persea americana, Peumus boldus, Phellodendron amurense, Phoebe cavaleriei, Photinia x fraseri, Pinus densiflora, Pinus douglasiana, Pipturus argenteus, Pistacia atlantica, Pistacia chinensis, Pistacia terebinthus subsp. palaestina, Pithecellobium sp., Pittosporum undulatum, Platanus mexicana, Platanus occidentalis, Platanus orientalis, Platanus racemosa, Platanus wrightii, Platanus x hispanica, Plumeria rubra, Podalyria calyptrata, Podocarpus henkelii, Populus alba, Populus brandegeei, Populus deltoides, Populus euphratica, Populus fremontii, Populus nigra, Populus simonii, Populus trichocarpa, Populus x canadensis, Populus x canescens, Protea mundii, Prunus africana, Prunus armeniaca, Prunus avium, Prunus caroliniana, Prunus cerasifera, Prunus cerasoides, Prunus domestica, Prunus dulcis, Prunus ilicifolia, Prunus mexicana, Prunus mume, Prunus nigra, Prunus persica var. nucipersica, Prunus persica, Prunus serrulata, Pseudobombax ellipticum, Pseudocydonia sinensis, Psidium guajava, Psoralea aphylla, Psoralea pinnata, Pterocarya stenoptera, Pyrus calleryana, Pyrus communis, Pyrus kawakamii, Quararibea funebris, Quercus acutissima, Quercus agrifolia, Quercus alba, Quercus brantii, Quercus calliprinos, Quercus castaneifolia, Quercus chihuahuensis, Quercus chrysolepis, Quercus dentata subsp. yunnanensis, Quercus engelmannii, Quercus frainetto, Quercus hartwissiana, Quercus ilex, Quercus infectoria, Quercus ithaburensis, Quercus lobata, Quercus look, Quercus macrocarpa, Quercus mexicana, Quercus myrsinifolia, Quercus palustris, Quercus pontica, Quercus robur subsp. pedunculiflora, Quercus robur, Quercus rubra, Quercus rugosa, Quercus suber, Quercus virginiana, Quercus x rosacea, Quercus x turneri, Rhamnus alaternus, Ricinus communis, Robinia pseudoacacia, Robinsonella discolor, Rosa sp., Roystonea regia, Salix acmophylla, Salix alba, Salix babylonica, Salix eastwoodiae, Salix exigua, Salix gooddingii, Salix laevigata, Salix lasiolepis, Salix mucronata, Salix nigra, Sambucus sp., Sapindus saponaria, Schinus longifolia, Schinus molle, Schinus polygama, Schinus terebinthifolia, Schotia brachypetala, Searsia chirindensis, Searsia lancea, Senegalia burkei, Senegalia caffra, Senegalia galpinii, Senna candolleana, Senna racemosa, Senna spectabilis, Senna x floribunda, Solanum granuloso-leprosum, Solanum mauritianum, Sparrmannia africana, Styphnolobium japonicum, Syzygium cordatum, Tamarindus indica, Tara cacalaco, Taxodium distichum, Terminalia mantaly, Tilia americana, Tilia caroliniana, Tipuana tipu, Toona ciliata, Trema orientale, Triadica sebifera, Trichilia emetica, Ulmus alata, Ulmus americana, Ulmus davidiana var. japonica, Ulmus glabra, Ulmus parvifolia, Ulmus procera, Umbellularia californica, Ungnadia speciosa, Vachellia campeachiana, Vachellia caven, Vachellia farnesiana, Vachellia karroo, Vachellia sieberiana var. woodii, Vachellia sieberiana, Vepris lanceolata, Verbesina gigantea, Vernicia fordii, Viburnum odoratissimum, Virgilia divaricata, Virgilia oroboides, Vitis vinifera, Washingtonia filifera, Wigandia urens, Wisteria floribunda, Wisteria sinensis, Xylosma congesta, Zelkova carpinifolia, Zelkova serrata, Zenia insignis, Ziziphus jujuba, Ziziphus spina-christi

All species within the Euwallacea fornicatus species complex are native to Asia and Oceania (Smith et al. 2019). Euwallacea fornicatus, considered to be native in China, Japan, Malaysia, Samoa, Sri Lanka, Taiwan, Thailand, and Vietnam, has been introduced into Argentina, Israel, South Africa, United States (California and Hawaii), and Europe (Ceriani-Nakamurakare et al., 2023; Eskalen et al., 2012; Mendel et al., 2012; Paap et al., 2018; Rugman-Jones et al., 2020; Schuler et al., 2022). Outbreaks of E. fornicatus (species complex) reported in Europe correspond to findings in greenhouses: Poland (Poznan-2019), Italy (Merano-2020), Netherlands and Germany (Berlin and Erfurt-2021) (Schuler et al., 2023). In Poland, Italy, Erfurt (Germany) and the Netherlands, the eradication of the plants (or infested part of the plants) resulted in the successful eradication of the beetles, whereas the eradication process in Berlin is reported to be still in progress.

EPPO Region: Israel
Africa: South Africa
Asia: China (Chongqing, Guizhou, Xianggang (Hong Kong), Yunnan), India (Uttar Pradesh, West Bengal), Israel, Japan (Ryukyu Archipelago), Malaysia (Sabah), Sri Lanka, Taiwan, Thailand, Vietnam
North America: United States of America (California, Hawaii)
South America: Argentina, Brazil (Ceara, Minas Gerais, Parana, Santa Catarina, Sao Paulo)
Oceania: Australia (Western Australia), Samoa

Most ambrosia beetle species attack only plants that died recently or are dying. However, a few species, including E. fornicatus, colonize healthy trees and cause damage through mass accumulation (Hulcr and Stelinski, 2017), where tree pathogens producing localized necrosis cause a significant amount of damage when inoculated by a large number of beetles (Smith & Hulcr, 2015).

Females of this species will typically make a divided or simple gallery encircling the stem, with a few longitudinal tunnels in small branches (Browne, 1961). Eggs are laid individually or in small clusters once the entrance tunnel has been completed. Diploid females produce haploid male offspring from unfertilized eggs, as is the case for other ambrosia beetles in the tribe Xyleborini. Newly emerged females stay in the galleries for several days where they are fertilized by the few brothers present. After mating, females leave the gallery through the original entrance hole (Browne, 1961). Adults develop in 22 days at 24°C (75°F), producing 57 female adults in 6 weeks, 7% of which are males (Cooperband et al., 2016).

The larvae, which has three instars (as typical of Xyleborini), feed entirely on symbiotic ambrosia fungi cultivated in longitudinal galleries of twigs and transverse galleries of thicker branches (Gadd, 1941). The fungi are transported to new trees in specialized pocket-like structures called mycangia (Batra, 1967). The fungi are obligate symbionts of the beetles and serve as their source of nutrition, with severe pathogenic effects for some plant species. The symbiotic fungus invades the tree vascular tissue, causing cambial necrosis, sugar or gum exudates, branch dieback, and mortality of a broad range of tree hosts (Eskalen et al., 2013). The symbiotic fungus Fusarium euwallaceae is associated with E. fornicatus, causing branch dieback once introduced (Eskalen et al., 2012; Freeman et al., 2013).

Symptoms

E. fornicatus bores and tunnels into the trunk, stems and branches of healthy trees and causes damage through mass accumulation. Females usually colonize the base of secondary branches, resulting in localized branch dieback. The symbiotic fungus invades the tree vascular tissue, causing cambial necrosis, sugar or gum exudates, branch dieback, and mortality of a broad range of tree hosts (Eskalen et al., 2013).

Morphology

Eggs

The eggs are very small, round and partly translucent, with a smooth surface. They are laid singly or in groups. Freshly laid eggs are pale, but they gradually darken before eclosion, hatching in 4 to 6 days.

Larva

The mature larva is about 3.5 mm long and 1.1 mm wide (Gardner, 1964). Larvae are white, legless, C-shaped, with a reddish head, taking 16-18 days to pupate. The head is colourless, about 0.5 mm wide, with the anterior margin nearly straight. The body integument is smooth except for a few scattered minute spicules.

Pupa

Pupae are similar in size to the adults and are white. Adults emerge after 7-9 days.

Adult

Females of the genus Euwallacea can only be distinguished from other Xyleborini by a combination of characters including unarmed pronotal margin, contiguous procoxae, having an obliquely costate dorsolateral margin of the pronotum, semicircular foretibiae, and have only sparse setae and small declivital denticles (Gomez et al., 2018). To identify specifically E. fornicatus, several morphological characters can be used, and all specimens fit within these measurement ranges (Smith et al., 2019). Total length is 2.60 mm − 2.70 mm. Elytral length of 1.44–1.72 mm, 8–9 socketed denticles in the margin of protibial. The pronotal width is 1.00–1.14 mm and the elytral width is 0.48–0.62 mm.

Detection and inspection methods

E. fornicatus is not attracted to ethanol (Dodge et al., 2017). Quercivorol and α-copaene have shown to be attractants, with synergistic effects increasing captures when combined (Dodge et al., 2017; Kendra et al., 2019). Sticky panels and black interception traps have been shown to be more efficient at capturing E. fornicatus than Lindgren traps (Kendra et al., 2019). Cooperband et al. (2017) suggested the existence of two pheromones, 2-heneicosanone and 2-tricosanone. Pheromones have rarely been reported for ambrosia beetles within the Scolytinae with just a few known examples (Borden et al., 1976; Borden & Slater, 1969; Francke & Heemann, 1974); these are probably involved in social behaviour inside galleries and the ecological and applied implications are yet to be tested.

Potential hosts, such as avocado, should be surveyed periodically for trees showing branch dieback and signs of beetle attack at junctions of small and mid-size shaded branches showing the presence of exit holes which have been described as white ‘sugar volcanoes’. Compacted frass and sawdust are also a (non-specific) sign of infestation, typically seen in the base of branches and in the trunk.

Active flight is one of the main means of movement to previously uninfested areas. Adult females can fly up to 400 m, but usually will attack hosts in a range of 35 m. However, the movement of timber and wood packaging material, such as dunnage and crating, has led to increasing transport and establishment of ambrosia beetles. The main pathway for ambrosia beetles such as E. fornicatus is wood packaging material and timber trade. Movements of infested host plants for planting can also transport all stages of the pest; attacks can be found on branches as small as 2 cm in diameter.

Economic impact

Severe economic impacts have been reported in Argentina, South Africa, California, Israel, and throughout Asia. E. fornicatus bores and tunnels into the trunk, stems and branches of healthy trees and causes damage through mass accumulation. Females usually colonize the base of secondary branches, resulting in localized branch dieback. Additionally, aside from negatively impacting the tree’s health, these attacks weaken its structure, posing a potential hazard to both people and property.

In Israel, E. fornicatus has caused severe impacts to the avocado industry (Mendel et al., 2012). In South Africa, it is considered the most damaging tree pest introduced in the country, with high impacts in urban environments (Paap et al., 2020). In Argentina, it was found colonizing the main trunks and the base of secondary branches of maples, although other hosts were reported (Ceriani-Nakamurakare et al., 2023). This colonization led to localized branch dieback and/or structural damage within a span of less than 12 months, while complete tree death typically occurs around 24 months. In California (United States), it poses a great ecological and environmental threat to infested areas by attacking a wide range of ornamental, and agriculturally important hardwood species hosts (Chen et al., 2020).

Control

Management is based on early detection, sanitation measures and preventive measures. Infested branches should be removed and destroyed (chipped, burned or buried). Heavily infested trees need to be destroyed (chipped, burned, or covered by a tarp under direct sun for ‘solarization’). Solarization works best using polyethylene sheeting during high temperature months, with ambient temperatures at least 35°C (95°F) (Jones & Paine, 2015).

Injecting systemic insecticides can help with protection of high-value ornamental trees. Preventative treatments with emamectin benzoate alone (systemic insecticide) or combined with propiconazole (systemic fungicide), reduces significantly the attack and colonization of E. fornicatus (Grosman et al., 2019). Injection into trees that are already infested typically does not work. Preventative insecticide sprays on bark surface work for ambrosia beetles, but need to be re-applied frequently because the effect only lasts between 4 and 8 weeks. Bark penetrant should be used to assure an extended effect.

Phytosanitary risk

A very wide range of host plants have been recorded for many of the species of Euwallacea and related genera. Any woody material of a suitable size and moisture content may be infested. The direct risk of establishment of populations of E. fornicatus into areas of the world outside its present distribution, and particularly into further tropical and subtropical parts of Africa and the Americas, should be considered as a serious threat to natural and planted ecosystems. In the EPPO region, incursions in glasshouses show that pathways for entry do exist, and the presence of E. fornicatus in Israel demonstrates that the pest has the potential to establish and cause damage on avocadoes in the Southern part of the region. Following a pest risk analysis, it has been considered that this insect (and its associated symbiont) was a serious threat to fruit crops and other woody plants grown for agricultural, forestry, and ornamental purposes (EPPO, 2021).

The increasing global movement of commodities has increased significantly the transport of E. fornicatus and related species in timber and wood packaging material, such as dunnage and crating. International Standards for Phytosanitary Measures No. 15 (ISPM 15) provides guidance for establishing measures to reduce the risk of pests associated with all types of wood packaging material. ISPM 15 affects all wood packaging material (pallets, crates, dunnage, etc.) and requires that they be debarked and then treated, and stamped or branded with a mark of compliance. Round wood or sawn wood (with or without bark) of host trees, as well as wood chips and other wooden products, should come from a pest free area or should have been treated to eliminate the pest. For host plants for planting, it may be required that they should originate from pest-free areas or pest-free production sites where plants are grown under physical isolation (EPPO, 2021).

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CABI and EFSA resources used when preparing this datasheet

CABI Datasheet on Euwallacea fornicatus: https://www.cabidigitallibrary.org/doi/10.1079/cabicompendium.18360453

This datasheet was prepared in 2024 by Demian Gomez. His valuable contribution is gratefully acknowledged.

EPPO (2024) Euwallacea fornicatus sensu stricto. EPPO datasheets on pests recommended for regulation. https://gd.eppo.int (accessed 2024-04-27)

This datasheet was first published online in 2024. It is maintained in an electronic format in the EPPO Global Database. The sections on 'Identity', ‘Hosts’, and 'Geographical distribution' are automatically updated from the database. For other sections, the date of last revision is indicated on the right.