Volatile attractants for three Pteromalid parasitoids attacking concealed spruce bark beetles

Abstract

The odour perceptive abilities, and preferences, of three bark beetle parasitoid species; Rhopalicus tutela (Walker), Roptrocerus mirus (Walker), and Roptrocerus xylophagorum (Ratzeburg) (Hymenoptera: Pteromalidae), were investigated to isolate and identify the essential compounds involved in host location. These parasitoids attack several economically important bark beetle species and oviposit preferentially on late larval stages concealed under the bark of conifers. Odours were collected from Norway spruce logs (Picea abies L. Karst.) containing Ips typographus L. (Coleoptera: Scolytidae) larvae. Biologically active compounds were isolated by coupled gas chromatographic-electroantennographic detection (GC-EAD), and identified by GC-mass spectrometry (GC-MS). Based on these analyses, four different synthetic baits were prepared and tested in a Y-tube walking bioassay. In the complex odour samples from spruce logs, only 16 compounds were EAD-active. The tested R. tutela and R. mirus females displayed similar trends in antennal activity to EAD-active compounds, responding mainly to oxygenated monoterpenes that indicate damaged conifers. Consequently, the synthetic baits were exclusively prepared with oxygenated monoterpenes. Parasitoid females (R. tutela and R. mirus) preferred spruce logs containing susceptible hosts over fresh logs, while male parasitoids (R. mirus) did not show any preference. However, when odours from fresh logs were mixed with synthetic baits (mimicking the odour composition of logs containing susceptible hosts), these combinations attracted female parasitoids (R. tutela, R. mirus, and R. xylophagorum). All synthetic baits seemed to be equally attractive to female parasitoids.

Semiochemicals from Fungal Associates of Bark Beetles May Mediate Host Location Behavior of Parasitoids

“…Studies on the chemistry of the host location cues of bark beetle parasitoids have demonstrated the importance of a group of approximately 7-15 cyclic monoterpene alcohols, ketones, and aldehydes. These oxygenated monoterpenes are consistently associated with conifer tissues infested with bark beetle larvae (Birgersson et al, 1992;Sullivan et al, 2000;Pettersson, 2001b), elicit strong antenna1 responses from several parasitoids of conifer-infesting bark beetles (Salom et al, 1991(Salom et al, , 1992Pettersson et al, 2000Pettersson et al, ,2001aPettersson, 2001a), and, in various combinations, are attractive to female parasitoids (Pettersson, 2001a;Pettersson et al, 2000,200la). Necrotic phloem surrounding sites on pine bolts inoculated with 0. minus or 0. ips contain elevated levels of 6-8 of these oxygenated monoterpenes (Sullivan, 1997), and bark beetle-associated yeasts and mycelial fungi grown in pure culture with conifer-derived substances also produce some of these compounds (Leufven et al, 1988;Sullivan, 1997).…”

Attraction of the Bark Beetle ParasitoidRoptrocerus xylophagorum(Hymenoptera: Pteromalidae) to Host-Associated Olfactory Cues

“…Many species of Coleopteran use tree terpenes as kairomones or pheromones (Byers 1992;Hobson et al 1993;Allison et al 2001Allison et al , 2004Thoss and Byers 2006). For instance, the volatile monoterpenes are often found serving as major attractants of Cerambycids (Allison et al 2004), bark beetles (Byers 1992; Hobson et al 1993;Thoss and Byers 2006), and a pine weevil (Nordlander 1990;1991), or as major chemical cues for natural enemies searching for pine herbivores (Pettersson 2001;Mumm and Hilker 2006). The present study showed that two populations of D. helophoroides adults also used terpenes as kairomones to look for their potential hosts.…”

“…Some parasitoids and predators utilize specific chemical cues from the frass of herbivores as a host-finding strategy (Grégoire et al 1991;Sullivan et al 2000;Pettersson 2001;Chuche et al 2006). There are three different populations of D. helophoroides in China that differ in their olfactory response to frass of different longhorned beetle species (Wei et al 2009c).…”

Exploitation of kairomones and synomones by Medetera spp. (Diptera: Dolichopodidae), predators of spruce bark beetles

“…The traps were baited with dispensers consisting of a cellulose pad, impregnated with the chemical(s) and sealed within polyethylene foil. The evaporation rate of each chemical is comparable to that associated with injured or attacked Norwegian spruce (Ikeda et al, 1980;Kydonieus & Beroza, 1982;Charlwood et al, 1991;Borg-Karlson et al, 1996;Baier et al, 1999;Pettersson, 2001). The used evaporation rates were (mg/day): -pinene -100; limonene -60; camphor -5; 2-methyl-3-buten-2-ol -100; S-cis-verbenol -5.…”

“…Hymenopteran parasitoids of I. typographus are attracted to oxidized monoterpenes such as camphor and isopinocamphon, which indicate advanced development of bark beetle brood (Pettersson, 2001, Pettersson & Boland, 2003. Since these parasitoids oviposit on bark beetle larvae in a late stage of development, their olfactory preferences correspond with factors that determine their reproductive success.…”