Location: Subtropical Horticulture ResearchTitle: Evaluation of Litchi chinensis for host status to Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae) and susceptibility to laurel wilt disease Author
Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/30/2013
Publication Date: 12/9/2013
Citation: Kendra, P.E., Ploetz, R.C., Montgomery, W.S., Niogret, J., Pena, J.E., Brar, G.S., Epsky, N.D. 2013. Evaluation of Litchi chinensis for host status to Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae) and susceptibility to laurel wilt disease. Florida Entomologist. Florida Entomol. 96 (4): 1442-1453. Interpretive Summary: The redbay ambrosia beetle (RAB) is an exotic wood-boring pest that transmits laurel wilt, a deadly fungal disease that threatens the avocado industry in Florida. To date, all known hosts for RAB and laurel wilt are species within the plant family Lauraceae. However, previous research by USDA-ARS scientists (Miami, FL) found that RAB is also highly attracted to, and will bore into, wood from lychee (family Sapindaceae), a fruit tree grown in Florida in close proximity to avocado groves. Therefore, a study was initiated by ARS and the University of Florida to evaluate two commercial cultivars of lychee, ‘Brewster’ and ‘Mauritius’, for host status to RAB and susceptibility to laurel wilt. RAB bored into live lychee trees, but after 3 months, there was no evidence of beetle reproduction and no signs of wilt disease. Moreover, lychee trees artificially inoculated with the fungal pathogen did not develop disease symptoms, and the fungus could not be detected in the trees 1 month after inoculation. Based on these results, it was concluded that lychee, despite its attractiveness to RAB, is not a reproductive host for the beetle and is not susceptible to laurel wilt disease. Action agencies and Florida growers will benefit from this information, since lychee is not a fruit crop affected by RAB or the lethal vascular disease it spreads.
Technical Abstract: The redbay ambrosia beetle, Xyleborus glabratus (Coleoptera: Curculionidae: Scolytinae), is an exotic wood-boring pest that vectors Raffaelea lauricola, the etiologic agent of laurel wilt. To date, all confirmed U.S. hosts of X. glabratus and suscepts of laurel wilt are members of the family Lauraceae. However, in previous research, an unknown variety of lychee, Litchi chinensis (Sapindales: Sapindaceae), was found to be highly attractive to X. glabratus and elicited boring behaviors. Therefore, a study was undertaken to evaluate two commercial cultivars of lychee, ‘Brewster’ and ‘Mauritius’, for susceptibility to attack by X. glabratus , for transmission of R. lauricola, and for development of laurel wilt disease. In no-choice laboratory bioassays, 35 and 44% of females bored into cut bolts of ‘Mauritius’ and ‘Brewster’, respectively. Similar boring was observed on the trunks of two live ‘Brewster’ trees; but after 3 mo, there was no evidence of beetle reproduction, no symptoms of laurel wilt, and no recovery of R. lauricola from tissue associated with beetle galleries. Lychee trees artificially inoculated with a virulent strain of R. lauricola (RL4) were asymptomatic after 1 mo, and assays for R. lauricola were negative. Chemical analysis indicated that lychee wood emits several sesquiterpene constituents in common with the Lauraceae, but at lower levels. Based on these data, we conclude that L. chinensis, although attractive to female X. glabratus, is not a reproductive host. This is apparently due to the inability of lychee wood to support growth of R. lauricola, the presumed primary nutritional symbiont of X. glabratus.