Lateral transfer of a phytopathogenic symbiont among native and exotic ambrosia beetles

Abstract

Different ambrosia beetle species can coexist in tree trunks, where their immature stages feed upon symbiotic fungi. Although most ambrosia beetles are not primary pests and their fungal symbionts are not pathogenic to the host tree, exceptional situations exist. Notably, Xyleborus glabratus carries a phytopathogenic symbiont, Raffaelea lauricola, which causes laurel wilt, a lethal disease of some Lauraceae species. Both X. glabratus and R. lauricola are natives of Asia that recently invaded much of the coastal plain of the southeastern USA. This study examined ambrosia beetles that breed in susceptible trees in Florida (USA), including avocado (Persea americana), redbay (P. borbonia) and swampbay (P. palustris). Raffaelea lauricola was recovered from six of eight ambrosia beetle species that emerged from laurel wilt-affected swampbay trees, in addition to X. glabratus. Controlled infestations with cohorts of the six species other than X. glabratus revealed that each could transmit the pathogen to healthy redbay trees and two could transmit the pathogen to healthy avocado trees; laurel wilt developed in five and one of the respective beetle 9 host interactions. These results indicate flexibility in the lateral transfer of a non-native ambrosial fungus to other ambrosia beetles, and for the first time documents the transmission of a laterally transferred phytopathogenic symbiont by new ambrosia beetle species. Additional work is needed to determine whether, or to what extent, the new beetle 9 R. lauricola combinations play a role in spreading laurel wilt.

The ambrosia symbiosis is specific in some species and promiscuous in others: evidence from community pyrosequencing

“…Still, one of the essential characteristics of the symbiosisspecificity-remains controversial. It has been traditionally assumed that ambrosia beetles are mostly associated with a single dominant fungus (Hubbard, 1896(Hubbard, , 1897Doane and Gilliland, 1929;Leach et al, 1940;Francke-Grosmann, 1956;Batra, 1963), but an increasing number of studies suggests that some beetle species may have more than one associate (Batra, 1966;Norris, 1979;Kü hnholz, 2004;Gebhardt et al, 2004;Carrillo et al, 2014). Recent experiments using cultured ambrosia fungi suggested that sympatric communities of ambrosia beetles may actually share a large pool of fungi and that horizontal symbiont exchange may be common (Carrillo et al, 2014).…”

Novel ophiostomatalean fungi from galleries of Cyrtogenius africus (Scolytinae) infesting dying Euphorbia ingens

“…Many ambrosia beetles carry more than one fungal partner and these fungi are often isolated together (Carrillo et al 2014, Kostovcik et al 2015. The association of ophiostomatalean fungi with C.…”

Laurel Wilt in Natural and Agricultural Ecosystems: Understanding the Drivers and Scales of Complex Pathosystems

“…The movement of symbionts amongst ambrosia beetle species had been recognized previously [69,71,73,74]. However, the magnitude and speed with which this has occurred for R. lauricola is unprecedented [70].…”

“…However, the magnitude and speed with which this has occurred for R. lauricola is unprecedented [70]. Since its introduction into the United States in or before 2002, R. lauricola has been horizontally transferred from X. glabratus to nine additional ambrosia beetle species [1,69,70,75,76].…”

“…Several other species are associated with redbay, avocado and other lauraceous hosts, but they have been considered as vectors of R. lauricola only recently. The general absence of X. glabratus in avocado orchards that are affected by laurel wilt, the pathogen's presence in other species of ambrosia beetle that are recovered from avocado and other host trees, and the experimental demonstration of pathogen transmission and subsequent laurel wilt development in redbay and avocado suggest that species other than X. glabratus could play roles in the epidemiology of this disease [1,69,70].…”