Volatilome of Australian Ips grandicollis-associated ophiostomatoid fungi

The eastern five-spined bark beetle (Ips grandicollis) is an invasive pine pest in Australia. This beetle is associated with a community of symbiotic ophiostomatoid fungi, including Ceratocystiopsis sp., Ophiostoma ips, Sporothrix pseudoabietina and the recently described Graphilbum ipis-grandicollis. Fungal volatile organic compounds (VOC) can mediate fungal-insect-host interactions, including host finding. We used solid phase microextraction to examine variation in VOC profiles of beetle-associated ophiostomatoid fungi over time and how these profiles are influenced by supplemental host monoterpenes (α- and β-pinene). We found significant differences in VOC profiles of four-day-old fungal cultures among the four fungal species. Twenty-one known volatile compounds were identified up to eighteen days following inoculation. One culture of each of Ophiostoma ips and Graphilbum ipis-grandicollis released cis-verbenol when grown on media amended with (−)-α-pinene. However, verbenone was only released from Graphilbum ipis-grandicollis when grown on media amended with (−)-α-pinene. These compounds are components of aggregation and anti-aggregation pheromones of I. grandicollis, respectively. Our results suggest that ophiostomatoid fungi could contribute to the chemical ecology of I. grandicollis, dependent on time and environmental factors such as growth conditions since colonization.