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

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.S1 Fig. Three dimensional chromatogram showing the two co-eluting peaks (A and B) eluting in the tail of the large major chromatographic peak released by males. The best tentative match for peak A was (Z)-3-decenol and peak B was (Z)-4-decenol in the NIST library.S2 Fig. Antennal recovery (in %) 30, 45 and 60 sec after 10 000 ng of (Z)-3-decenol puffed (n = 3 males and 3 females). Different letters indicate significant differences of the recovery time.The United State Department of Agriculture-Forest Service Forest Health Protection (USDA-FS FHP), National Resources Canada (NRCan), the Tree Protection Cooperative Program (TPCP) and the DSI NRF Center of Excellence in Plant Health Biotechnology (CPHB) in South Africa.http://www.plosone.orgam2021BiochemistryChemistryForestry and Agricultural Biotechnology Institute (FABI)GeneticsMicrobiology and Plant PathologyZoology and Entomolog