Symbionts mediate oviposition behaviour in invasive and native woodwasps

Abstract

1 Globalization leads to the introduction of invasive species that are often accompanied by associated microorganisms, and this can lead to homogenization of both introduced hosts and microbes with the native biota. One such example is the invasive Eurasian woodwasp Sirex noctilio, which inoculates pines with an obligate nutritional mutualist, the white rot fungus Amylostereum areolatum. 2 Although S. noctilio has been previously introduced outside of its native range, its arrival in North America was the first time that it was introduced to communities hosting native Sirex species and Amylostereum strains. 3 We conducted experiments aiming to investigate acceptance versus avoidance of native and non-native Amylostereum strains and species during ovipositor drilling by females of S. noctilio and a native congener, Sirex nigricornis. 4 Sirex noctilio preferred wood without prior fungal emplacement, whereas S. nigricornis preferred wood inoculated with one of the strains of Amylostereum that putatively invaded with S. noctilio. 5 Drilling and presumed oviposition by both woodwasp species were highly aggregated. 6 Based on the responses of these two Sirex species to the fungal strains and species included in the present study, the invasive S. noctilio would continue its present symbiont associations, whereas the native S. nigricornis would partly use the strain of fungal symbiont putatively introduced with S. noctilio.

Community resistance to an invasive forest insect–fungus mutualism

“…The wounding treatment served as a control for the biological aspects of Sirex oviposition: It replicated the aggregation of drills observed in field surveys (Hajek et al. ) as well as the physical damage to trees, but lacked female wasps, eggs, symbiotic fungus, and toxic mucous of Sirex attacks. Within each year, all treatment units were initiated and opened on the same day, and across years, these initiation events corresponded roughly to the peak emergence season for Sirex in the region (approximately August 1–15).…”

“…This treatment matched the number and dispersion of oviposition drills observed in the Sirex-addition treatment within the replicate after 72 h, although artificially drilled trees released more resin than matched Sirex-damaged trees (BMT personal observation). The wounding treatment served as a control for the biological aspects of Sirex oviposition: It replicated the aggregation of drills observed in field surveys (Hajek et al 2018) as well as the physical damage to trees, but lacked female wasps, eggs, symbiotic fungus, and toxic mucous of Sirex attacks. Within each year, all treatment units were initiated and opened on the same day, and across years, these initiation events corresponded roughly to the peak emergence season for Sirex in the region (approximately August 1-15).…”

Functional and Compositional Changes in Sirex noctilio Gut Microbiome in Different Habitats: Unraveling the Complexity of Invasive Adaptation

“…The frequency of invasions of numerous insects into new niches is increasing worldwide, which has caused forest ecosystem damage and economic losses [ 2 , 3 ]. The introduction of invasive species is often accompanied by associated microorganisms, and together, they form a unit made up of the hosts and microbes with the native biota [ 4 ]. Insects are colonized by different microorganisms, which are often beneficial or required by the hosts [ 5 ].…”

Oviposition substrate location by the invasive woodwasp Sirex noctilio: the combined effect of chemical cues emitted by its obligate symbiont Amylostereum areolatum and different host‐tree species

“…This novel association between A. areolatum and a second Siricid species is thought to be due to the recent introduction of S. noctilio to the area. [13][14][15] The fungus is transported by the females in special structures called mycangia 16 and is essential for larval development due to its role in their nutrition. 17,18 The fungus mycelia are initially inoculated into trees during oviposition together with a phytotoxic venom.…”

“…However, more recent studies indicate that other siricids native to North America, where S. noctilio has recently arrived, can carry A. areolatum in mycangia. This novel association between A. areolatum and a second Siricid species is thought to be due to the recent introduction of S. noctilio to the area 13–15 . The fungus is transported by the females in special structures called mycangia 16 and is essential for larval development due to its role in their nutrition 17,18 .…”