Semiochemicals produced by fungal bark beetle symbiont Endoconidiophora rufipennis and the discovery of an anti-attractant for Ips typographus

Abstract

Bark beetles vector symbiotic fungal species into their host trees during mass attacks. The symbiotic relationship with blue stain fungi of the Ascomycetes, including genera of Endoconidiophora (syn. = Ceratocystis), promotes successful establishment whereby the microbes help to overcome the host trees’ defence and degrade toxic resins. This is the first study to evaluate both the volatile emissions from an insect-associated blue stain fungus over time and the insect response in a field trapping experiment. Volatile emissions from isolates of Endoconidiophora rufipennis (ER) were collected by solid-phase microextraction (SPME) and analysed by gas chromatography—mass spectroscopy (GC-MS) over a period of 30 days. This virulent North American fungus is closely related to E. polonica, a symbiotic fungus known from Eurasian spruce bark beetle Ips typographus.Nine volatiles were emitted by ER in substantial amounts: isoamyl acetate, sulcatone, 2-phenethyl acetate, geranyl acetone, geranyl acetate, citronellyl acetate, (R)- and (S)-sulcatol, and (R)-sulcatol acetate. A late peaking compound was geranyl acetone. In the field trapping experiment, three of the fungal volatiles (geranyl acetone, 2-phenethyl acetate and sulcatone) were tested in combination with a synthetic aggregation pheromone for I. typographus. Traps with geranyl acetone attracted lower numbers of I. typographus compared to traps with 2-phenethyl acetate, sulcatone or the pheromone alone as a control. The results showed that geranyl acetone acts as an anti-attractant and may act naturally on I. typographus as a cue from an associated fungus to signal an overexploited host.

How Effective Are Push–Pull Semiochemicals as Deterrents for Bark Beetles? A Global Meta-Analysis of Thirty Years of Research

“…According to Fettig et al [66], various studies conducted in north-western North America found acetophenone, (E)-2-hexen-1-ol + (Z)-2-hexen-1-ol, and verbenone provided significant protection to ponderosa pines from D. brevicomis attacks. Our results were aligned with the findings of Gaylord et al [54] and Lindmark, et al [70] for I. pini in south-western United States and I. typographus in Scandinavia, respectively.…”

“…scopulorum Engelm., trees from Ips attacks [54]. Like our findings, Lindmark et al [70] also reported a reduction in bark beetle capture using an attractant-repellent approach and suggested using semiochemicals as an effective alternative to insecticides for reducing the bark beetle population.…”

The Female-Biased General Odorant Binding Protein 2 of Semiothisa cinerearia Displays Binding Affinity for Biologically Active Host Plant Volatiles

“…The ScinGOBP2 ligands can elicit antennal responses in both male and female individuals, indicating that these volatile compounds released by plants might serve as potential semiochemicals for S. cinerearia. Plant volatiles such as dipentene, decanal, cis-3-hexenyl n-valerate, and geranyl acetone have been shown to act as repellents and/or attractants for some insects [34][35][36][37][38]. In the present study, different ScinGOBP2 ligands at the same concentrations elicited different behaviors in S. cinerearia.…”

Field effects of oxygenated monoterpenes and estragole combined with pheromone on attraction of Ips typographus and its natural enemies

“…Anti-attractant blends offer partial protection for standing trees but are ineffective for windfallen trees. Adding new anti-attractants, e.g., geranyl acetone (Lindmark et al, 2023), to the mixture may enhance tree protection effects.…”