Courtship behavior and identification of a sex pheromone in Ibalia leucospoides (Hymenoptera: Ibaliidae), a larval parasitoid of Sirex noctilio (Hymenoptera: Siricidae).

BACKGROUND: Ibalia leucospoides (Hymenoptera: Ibaliidae) is a larval parasitoid that has been widely introduced as a biological control agent for the invasive woodwasp,Sirex noctilio (Hymenoptera: Siricidae) in the Southern Hemisphere. In this study, the courtship behavior and identificaion of sex pheromones are described for I. leucospoides under laboratory conditions. METHODS: For courtship behavior, both sexes were observed in a wire mesh observation cylinder (75 cm length ×10 cm diameter) for 15 minutes. The female body washes were analyzed using Gas Chromatography- Electroantennographic Detection (GC-EAD). Then the EAD-active compounds were tentatively identified using GC-Mass Spectrometry (GC-MS) and examined in olfactometer assays. RESULTS: The courtship behavior included rhythmic lateral movements, mounting, head-nodding cycles in males, and wing-fanning in females. GC-EAD analysis of female body washes with male antennae revealed seven compounds which elicited antennal responses, four of which are straight-chain alkanes (C23, C25, C26, and C27). The identities of these alkanes were confirmed by matching the retention times, mass spectra, and male antennal activity to those of commercially obtained chemicals. In olfactometer assays, a blend of the four straight-chain alkanes was attractive to I. leucospoides males, and there was no response to blends that lacked any of these four compounds. Female body wash was no more attractive than the four-component blend. The ratios of EAD-active components differ between hydrocarbon profiles from males and females. CONCLUSION: This study is the first investigation of cuticular hydrocarbons in the family Ibaliidae. It provides evidence that the ubiquitous alkanes (C23, C25, C26, and C27) in sex-specific ratios attract I. leucospoides males.

Steps in the biosynthesis of fuscumol in the longhorn beetles Tetropium fuscum (F.) and Tetropium cinnamopterum Kirby.

Fuscumol [(2S,5E)-6,10-dimethyl-5,9-undecadien-2-ol] was recently identified as the male-produced aggregation pheromone of the brown spruce longhorn beetle, Tetropium fuscum (F.), and the eastern larch borer, Tetropium cinnamopterum Kirby. Several other species use this homoterpenoid alcohol motif, its ketone, or its acetate as part of their pheromone system. Investigation of the biosynthesis of this compound in these two Tetropium species demonstrated that geranylacetone [(5E)-6,10-dimethyl-5,9-undecadien-2-one] and farnesol [(2E,6E)-3,7,11-trimethyl-2,6,10-dodecatrien-1-ol] are both intermediates in this process. This was accomplished by applying deuterium-labeled geranylacetone and deuterium-labeled farnesol in separate experiments to the abdominal sterna of live T. fuscum and T. cinnamopterum and analyzing the deuterium labeling in the fuscumol and geranylacetone emitted by the insects with solid-phase microextraction (SPME) and GC/MS analysis. Deuterium labeling studies also showed that nerolidol[(3S,6E)-3-hydroxy-3,7,11-trimethyl-1,6,10-dodecatriene] and 2,3-epoxyfarnesol are not intermediates in fuscumol or geranylacetone synthesis in T. fuscum or T. cinnamopterum. Tissue-specific expression of T. fuscum farnesyl diphosphate synthase (TfFPPS), an enzyme expected to provide a key fuscumol precursor, was measured. TfFPPS transcripts were relatively abundant in male midguts, but were also present at significant levels in other tissues.

Contact sex pheromones identified for two species of longhorned beetles (Coleoptera: Cerambycidae) Tetropium fuscum and T. cinnamopterum in the subfamily Spondylidinae.

Male Tetropium fuscum (F.) and T. cinnamopterum Kirby mated with live and dead (freeze-killed) conspecific females upon antennal contact, but did not respond to dead females after cuticular waxes were removed by hexane rinsing. Significantly fewer males of each species attempted to copulate with live or dead heterospecific females than with conspecifics, indicating that mate recognition was mediated by species-specific contact sex pheromones in the female's cuticular hydrocarbons. GC/MS analysis of T. fuscum elytra identified n-alkanes and mono-methyl branched alkanes of which 11-methylheptacosane and 3- and 5-methyltricosanes were dominant in females. Full male responses, including copulatory behavior, were restored with application of enantiomerically pure synthetic (S)-11-methyl-heptacosane at 40 µg/female (one female equivalent) but not with racemic or (R)-11-methyl-heptacosane. The cuticular hydrocarbons on T. cinnamopterum elytra included 11-methyl-heptacosane as well as n-alkanes, methyl-branched alkanes, mono-alkenes, and (Z, Z)-6, 9-alkadienes. (Z)-9-pentacosene, (Z)-9-heptacosene, and 11-methyl-heptacosane were female dominant, but only (Z)-9-pentacosene elicited precopulatory behaviors in conspecific males at levels similar to those behaviors elicited by unrinsed females, but elicited copulation in fewer than half of males. At female equivalent dosages (10 µg), neither (Z)-9-heptacosene nor (S)-11-methyl- heptacosane elicited responses in males that were significantly different from those responses to a rinsed female but when applied together, the proportion of males responding was significantly increased. 11-methyl-heptacosene is thus a contact pheromone component common to both species, which may explain the heterospecific mating attempts by some males.

Effect of chirality, release rate, and host volatiles on response of Tetropium fuscum (F.), Tetropium cinnamopterum Kirby, and Tetropium castaneum (L.) to the aggregation pheromone, fuscumol.

The male-produced aggregation pheromones of Tetropium fuscum (F.) and T. cinnamopterum Kirby were identified as (2S,5E)-6,10-dimethyl-5,9-undecadienol by chemical analysis, synthesis, electronantennography, and field trapping; the compound is here renamed "fuscumol". The effect of fuscumol chirality, alone or with host volatiles, and fuscumol release rate on Tetropium spp. was tested in field-trapping experiments in Nova Scotia and Poland. Both (S)-fuscumol and racemic fuscumol synergized trap catches of male and female T. fuscum, T. cinnamopterum, and T. castaneum (L.) when combined with a blend of host monoterpenes and ethanol. Without added host volatiles, fuscumol was either unattractive (in Nova Scotia) or only slightly so (in Poland). (R)-Fuscumol, alone or in combination with host volatiles, did not elicit increases in trap capture of any Tetropium species, relative to the controls. Fuscumol synergized attraction of both sexes to host volatiles, thus indicating it acts as an aggregation pheromone. Sex ratio was often female-biased in traps baited with fuscumol plus host volatiles, and was either unbiased or male-biased in traps with host volatiles alone. In traps with host volatiles and racemic fuscumol, mean catches of Tetropium species were unaffected by fuscumol release rates ranging from 1 to 32 mg/d. The attraction of three different Tetropium species to the combination of (S)-fuscumol and host volatiles suggests that cross-attraction may occur where these species are sympatric, and that reproductive isolation possibly occurs via differences in close-range cues. These results have practical applications for survey and monitoring of T. fuscum, a European species established in Nova Scotia since at least 1980, and for early detection of T. castaneum, a European species not presently established in North America.