Fusarium euwallaceae sp. nov.—a symbiotic fungus of Euwallacea sp., an invasive ambrosia beetle in Israel and California

Abstract

The invasive Asian ambrosia beetle Euwallacea sp. (Coleoptera, Scolytinae, Xyleborini) and a novel Fusarium sp. that it farms in its galleries as a source of nutrition causes serious damage to more than 20 species of live trees and pose a serious threat to avocado production (Persea americana) in Israel and California. Adult female beetles are equipped with mandibular mycangia in which its fungal symbiont is transported within and from the natal galleries. Damage caused to the xylem is associated with disease symptoms that include sugar or gum exudates, dieback, wilt and ultimately host tree mortality. In 2012 the beetle was recorded on more than 200 and 20 different urban landscape species in southern California and Israel respectively. Euwallacea sp. and its symbiont are closely related to the tea shot-hole borer (E. fornicatus) and its obligate symbiont, F. ambrosium occurring in Sri Lanka and India. To distinguish these beetles, hereafter the unnamed xyleborine in Israel and California will be referred to as Euwallacea sp. IS/CA. Both fusaria exhibit distinctive ecologies and produce clavate macroconidia, which we think might represent an adaption to the species-specific beetle partner. Both fusaria comprise a genealogically exclusive lineage within Clade 3 of the Fusarium solani species complex (FSSC) that can be differentiated with arbitrarily primed PCR. Currently these fusaria can be distinguished only phenotypically by the abundant production of blue to brownish macroconidia in the symbiont of Euwallacea sp. IS/CA and their rarity or absence in F. ambrosium. We speculate that obligate symbiosis of Euwallacea and Fusarium, might have driven ecological speciation in these mutualists. Thus, the purpose of this paper is to describe and illustrate the novel, economically destructive avocado pathogen as Fusarium euwallaceae sp. nov. S. Freeman et al.

PCR Multiplexes DiscriminateFusariumSymbionts of InvasiveEuwallaceaAmbrosia Beetles that Inflict Damage on Numerous Tree Species Throughout the United States

“…within the E. fornicatus species complex have been confirmed attacking native vegetation in many new areas throughout San Diego, Los Angeles, Orange, and Riverside Counties (Boland 2016;Lynch et al 2016). Avocado has also been affected in California, Israel, and partially in Florida, although the severity of damage is highly variable regionally and temporally (Mendel et al 2012;Freeman et al 2013). Future introductions of exotic beetles are anticipated and the ranges of established polyphagous Euwallacea spp.…”

“…However, some of them are able to colonize living trees, sometimes in massive numbers, and the joint action of the wood borer and their cultivated fungi can cause symptoms known as Fusarium dieback or Fusarium canker. The greatest impact has been reported from the polyphagous shot hole borer on avocado and boxelder in California and Israel, which farms Fusarium euwallaceae S. Freeman, Z. Mendel, T. Freeman et al 2013). However, similar testing is needed to confirm pathogenicity and host range of Fusarium stains associated with other introduced Euwallacea spp.…”

The Role of Mites in Bark and Ambrosia Beetle-Fungal Interactions

“…In another example, an Euwallacea sp. ambrosia beetle is causing damage to more than twenty tree species in California, with particular concern to avocado [12]. The damage is caused by the spread of a novel Fusarium fungus causing tree wilting and dieback [12].…”

“…Fungi allow ambrosia beetles to exploit the wood that would have otherwise been a nutritionally poor resource, as well as exploit living trees. In California and Israel, an invasive ambrosia beetle poses a serious threat to avocado plantations via the introduction of a Fusarium fungus species causing dieback, wilting, and ultimately host tree mortality [12]. Similarly, adult leaf-cutter ants (Attini: Atta or Acromyremex) use leaves to foster the cultivation of fungi inside their colonies, which they in turn use as a food source [13], resulting in large-scale defoliation of nearby trees [14].…”

Extremely low infection levels of pathogens and nematodes in Trypodendron spp. (Coleoptera: Curculionidae)

“…The beetles typically attack trees that have been cut or weakened by disease, but some taxa attack apparently healthy trees (Kühnholz et al 2001). In addition to reducing value of wood products by generating pinholes and staining, the beetles can also vector fungi that are highly pathogenic to living trees (Hulcr & Dunn 2011;Suh et al 2011;Evans et al 2013;Freeman et al 2013;Carrillo et al 2014).…”