Volatile emissions and relative attraction of the fungal symbionts of tea shot hole borer (coleoptera: curculionidae)

Authors: Kendra, Paul; CRUZ, LUISA - University Of Florida; Tabanca, Nurhayat; MENOCAL, OCTAVIO - University Of Florida; Schnell, Elena; CARRILLO, DANIEL - University Of Florida

Submitted to: Biomolecules EISSN 2218-273X
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2022
Publication Date: 1/7/2022
Citation: Kendra, P.E., Cruz, L.F., Tabanca, N., Menocal, O., Schnell, E.Q., Carrillo, D. 2022. Volatile emissions and relative attraction of the fungal symbionts of tea shot hole borer (coleoptera: curculionidae). Biomolecules EISSN 2218-273X. 12(1):97. https://doi.org/10.3390/biom12010097.
DOI: https://doi.org/10.3390/biom12010097

Interpretive Summary: The tea shot hole borer is an ambrosia beetle that spreads a fungus that causes Fusarium dieback, a destructive vascular disease of avocado trees in Florida. The beetle is currently detected with lures containing quercivorol, a food-based attractant produced by the beetle’s fungal symbionts. The lure contains a mixture of compounds, so the exact attractant is unknown. In addition, the beetle carries multiple fungal symbionts, and it is not known which fungi produce beetle attractants. Therefore, scientists from the USDA-ARS (Miami, FL), in collaboration with the University of Florida (Homestead), conducted research with pure cultures of six symbionts isolated from the beetle. Gas chromatography-mass spectroscopy was used to identify and quantify the volatiles emitted by each symbiont. Lab bioassays were conducted to determine which fungi were attractive to beetles. The chemical analysis revealed that only one compound, trans-p-menth-2-en-1-ol, was produced by all six symbionts. The most attractive symbiont, a new species of Fusarium, only produced two volatiles: trans-p-menth-2-en-1-ol and limonene. Identification of these two attractants will facilitate development of improved lures for early detection of tea shot hole borer, helping action agencies and avocado growers manage the spread of Fusarium dieback disease in commercial groves.

Technical Abstract: Euwallacea perbrevis is an ambrosia beetle that vectors a fungal pathogen causing Fusarium dieback in Florida avocado trees. Current monitoring lures contain quercivorol, a fungus-produced volatile, but the exact attractant is unknown since lures contain a mixture of p-menth-2-en-1-ol isomers and both a- and ß-phellandrene. This study used pure cultures of six symbiotic fungi isolated from E. perbrevis to document volatile emissions and determine the relative attraction of symbionts in binary choice assays. In a comparative test, headspace solid-phase microextraction followed by gas chromatography-mass spectroscopy was used to identify and quantify emissions from 3-wk-old cultures. In a temporal study, Super-Q collection followed by gas chromatography-flame ionization detection was used to measure cis- and trans-p-menth-2-en-ol emissions for three months. A total of 15 compounds were detected, with monoterpene hydrocarbons and oxygenated monoterpenoids predominating. Only trans-p-menth-2-en-1-ol was common to all six symbionts. Peak levels of both isomers were observed at day 7, then gradually declined over a 90-day period. In choice tests, avocado sawdust disks inoculated with Fusarium sp. nov. were the most attractive. This symbiont produced only two volatiles, trans-p-menth-2-en-1-ol and limonene. The combined results indicate that trans-p-menth-2-en-1-ol is the primary female attractant emitted from symbiotic fungi, but limonene may be a secondary attractant of E. perbrevis.