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Pheromone blend investigation in a pine killer, the European woodwasp Sirex noctilio

Quentin Guignard^a, Marc Bouwer^b, Jeremy Allison^a,c, Bernard Slippers^d

^a Department of Zoology and Entomology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria 0002, South Africa

^b Department of Chemistry, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria 0002, South Africa

^c Natural Resources Canada, Canadian Forest Service, Great Lakes Forestry Centre, 1219 Queen Street E, Sault Ste. Marie, Ontario, P6A 2E5, Canada

^d Department of Biochemistry, Genetics and Microbiology, Forestry and Agricultural Biotechnology Institute, University of Pretoria, Pretoria 0002, South Africa

Keywords: Chemical ecology, Sirex noctilio, male pheromone, dose-response, hind legs

The European woodwasp Sirex noctilio has been introduced in Southern hemisphere where it is an important threat for the pine industry. Females drill holes through the bark of the tree to lay their eggs, which develop into larvae feeding on the wood. Successful larval development is almost always associated with multiple attacks and tree death. None of the actual control methods guarantee an economically stable threshold of infestation. New approaches must be find to control the wasp. Insects typically communicate via volatile molecule called pheromones which can have a strong attractive effect. Pheromones are good target to develop a long range attractant that can be exploited to trap pests. In this study, we investigated three aspect of the pheromone blend in S. noctilio:

i) Compound identification in the pheromone blend. We used gas-chromatography analyses and analytical chemistry to identified four compounds emitted by the males. One major compound: the Z-3-decenol, and three minor compounds: the Z-3-Octenol, Z-4-decenol and Z-3-dodecenol.

ii) Antennal sensitivity of each compounds. Different doses of each compounds were screened on antennae of both males and females with an electroantennogram detector. Electrophysiological responses show that both males and females are sensitive to the four compounds. The Z-3-Octenol shows a significantly bigger response than the other compounds, especially on the female antenna. The z-3 and z-4-decenol elicit a similar response between them. For each doses tested, both males and females had homogeneous responses for the z-3-decenol. Female were usually more sensitive to the z-4-decenol. Finally, the Z-3-dodecenol elicited the smallest response of all the four compound and were similar between sexes.

iii) Provenance of the pheromone blend. Insects were cut into pieces and the quantity of each compound was measure by gas-chromatography. We identified the source of the pheromone blend to be emitted from the hind legs of the males. The strong sexual dimorphism of the hind legs and literature suggest that the pheromone blend could be involve in attraction as a trail, aggregation or sexual pheromone.

Investigating pheromone composition, reaction and production are crucial aspect for the development of a long range attractant. This study provides new insight on a potential pheromone blend that can be used the trap S. noctilio. We are currently testing this blend of compounds in different ratio in the South-African plantation.