Biology of a putative male aggregation-sex pheromone in Sirex noctilio (Hymenoptera: Siricidae)

Abstract

A putative male-produced pheromone has recently been described for the global pest of pines, Sirex noctilio, but field-activity has not been demonstrated. This study aimed to investigate the pheromone biology of S. noctilio in more detail. Specifically, we i) analysed effluvia and extracts for additional compounds by gas chromatography coupled with electro-antennographic detection (GC-EAD), mass spectrometry (GC-MS) and two dimensional time of flight mass spectrometry (GC X GC TOF MS), ii) conducted dose-response experiments for putative pheromone components, iii) determined the site of synthesis/ storage of the putative pheromone and iv) determined the release rate of the putative pheromone from males and three types of lures. A blend of four compounds was identified, including the previously described (Z)-3-decenol and (Z)-4-decenol, and two new compounds (Z)-3-octenol and (Z)-3-dodecenol. All compounds elicited a response from both male and female antennae, but the strength of the response varied according to sex, compound and dose tested. (Z)-3-Decenol and (Z)-3-octenol at lower and higher doses, respectively, elicited larger responses in males and females than the other two compounds. (Z)-3-Octenol and (Z)-4-decenol generally elicited larger female than male antennal responses. The site of synthesis and/or storage in males was determined to be the hind legs, likely in the leg-tendon gland. The relative release rate of the major compound by male wasps was shown to be 90 ± 12.4 ng/min, which is between 4 and 15 times greater than that observed from typical lures used previously. These observations are consistent with the hypothesis that these compounds may mediate lek formation in S. noctilio males and lek location in females.

Key Residues Affecting Binding Affinity of Sirex noctilio Fabricius Odorant-Binding Protein (SnocOBP9) to Aggregation Pheromone

“…Meanwhile, studies have shown that release and storage of aggregated pheromones in S. noctilio may originate from the leg tendon gland of the hind legs, which is a centrally controlled storage. The leg tendon gland is a hollow reservoir starting in the femur and running down to the unguitractor plate, manubrium and arolium structures situated at the end of the clamp [ 48 ]. With a similar structure such as the tracer pheromone released by ant Crematogaster , which comes from the tibial tendon gland of their hind legs [ 60 ], females in Ascogaster reticulatus release ( Z )-9-hexadecenal as a sex pheromone from the hind legs [ 61 ]; male Polistes dominulus are thought to release a lek-formation pheromone from their legs [ 62 ]; foragers in the stingless bee Melipona seminigra use a pheromone from the hind leg tendon gland to mark their food sites [ 63 ].…”

“…Only Z3D was identified from the S. noctilio Chinese population, and the peak of Z3D release occurred from 11:00–12:00 for two-day-old individuals, which can elicit antennal response consistently in our GC-EAD assays ( Figure S1 ) [ 45 , 46 , 47 ]. Two putative male aggregation pheromones in S. noctilio that have not been validated in field-activity were identified as ( Z )-3-octen-ol and ( Z )-3-dodecen-ol; these two new substances were not identified in our previous experiments [ 48 ]. This pheromone-related research indicated that Z3D plays an important role in regulating the behavioral rhythm of woodwasps.…”

Biologically active cuticular compounds of female Sirex noctilio

“…The male swarms of S. noctilio contrast with the definition of the classical lek‐forming species, in which males compete for territories that contain no resources vital to females, except copulation and mating (Thornhill & Alcock, 1983; Bradbury & Gibson, 1983; Shelly & Whittier, 1997). However, in support of the lek hypothesis, Allison et al (2021) reported the attraction of females to traps baited with only dead males, and Guignard et al (2020) discovered two electroantennographically detected (EAD) compounds – ( Z )‐3‐octenol and ( Z )‐3‐dodecenol – which are released from the hind legs of males, and elicited antennal responses from both sexes.…”

“…with only dead males, and Guignard et al (2020) discovered two electroantennographically detected (EAD) compounds -(Z)-3-octenol and (Z)-3-dodecenol -which are released from the hind legs of males, and elicited antennal responses from both sexes.…”

Evidence for UV-green dichromacy in the basal hymenopteran Sirex noctilio (Siricidae)

“…Field studies have reported that males aggregate at the top of pine trees to form leks and females are attracted to these for mating 25 – 27 . A male specific putative pheromone released from the sexually dimorphic hind legs has been described 28 . We refer to this as a putative pheromone because although attraction was observed in the lab 29 , it was inactive in field trials 30 suggesting that other sensory modalities than olfaction could play an important role in mate attraction.…”