Behavioural response of the woodwasp Sirex noctilio to volatile emissions of its fungal symbiont

Abstract

The wood-boring wasp, Sirex noctilio, is a global invasive pest that infects and kills pine trees by inoculating spores of a symbiotic fungus (Amylostereum areolatum) at oviposition. Wasp larvae depend on fungal growth to feed, while the fungus relies on female wasps to initially condition the pine tree by inoculating a phytotoxic venom and for dispersal. Wasp larvae use the fungus as an external gut for the digestion of lignocellulosic compounds resulting in a strong correlation between fungal growth inside the wood and wasp fitness. This study explores the hypothesis that female wasps will use fungal volatiles as a synomone in the process of locating suitable oviposition areas (i.e. trees). Using a Y-tube olfactometer, adult female wasp behaviour was assessed towards fungal and pine tree volatiles (i.e. positive control). Our results are the first to demonstrate attraction of female S. noctilio towards volatiles of their fungal symbiont. Furthermore, the positive response towards these volatiles seems to be stronger than the response to a known attractant (i.e. pine volatiles). These results could be an important contribution to improving baits for monitoring and control purposes. Further work is needed, mainly oriented towards the identification of the volatiles that trigger the observed attraction response and their possible synergistic effects with tree volatiles.

Beneath the bark: associations among Sirex noctilio development, bluestain fungi, and pine host species in North America

“…Variability in pine colonisation could be because of the host volatile profile. Sirex noctilio exhibits positive chemotaxis to pine monoterpenes (Fernández Ajó et al ., ) and an α : β pinene blend (70 : 30) is currently used for trapping. In the field, Böröczky et al .…”

“…Variability in pine colonisation could be because of the host volatile profile. Sirex noctilio exhibits positive chemotaxis to pine monoterpenes (Fernández Ajó et al, 2015) and an : pinene blend (70 : 30) is currently used for trapping. In the field, Böröczky et al (2012) found that P. sylvestris trap trees of a high -3-carene chemotype captured more S. noctilio than low -3-carene chemotype P. sylvestris or P. strobus; however, this pattern did not translate to more S. noctilio emergents in attacked hosts.…”

Symbionts mediate oviposition behaviour in invasive and native woodwasps

“…However, the proportion of drill clusters that were pre‐conditioning (one drill/cluster) versus presumably egg‐laying (≥ 2 drills/cluster) did not differ across treatments. Less drilling by S. noctilio into bolts inoculated with A. areolatum could have been an active choice because we know that S. noctilio females can detect A. areolatum volatiles (Fernández Ajó et al ., ; Sarvary et al ., ). Drilling by S. noctilio in bolts inoculated with Aa BD, which is assumed to have been introduced to North America with S. noctilio , was intermediate.…”

Effects of endophytic fungi in Mongolian pine on the selection behavior of woodwasp (Sirex noctilio) and the growth of its fungal symbiont

“…Currently, the most common methods used to weaken host trees are ring cutting and herbicide injection; however, these methods result in the death of the host tree. Fernández Ajó and coworkers showed that volatiles from symbiont are capable of attracting adult woodwasps, and the attractant ability of symbiont volatiles is better than that of host volatiles . However, volatile organic compounds (VOCs) of symbiotic fungus were not assayed in his study.…”