Sirex Woodwasp

Sirex Woodwasp
Sirex noctilio
Wood boring

Pine needles wilt, turn yellow and then brown within a month after attack. Small resin droplets are visible on the bark of stems where the ovipositor penetrated. Larval tunnels can be observed in the sapwood – circular in cross section and tightly packed with a fine wood frass. When the adults emerge they leave perfectly circular emergence holes (3-10mm in diameter), which go through the bark and into the sapwood.

 

A fairly large (7-40 mm), metallic black-blue wasp with two pairs of brownish membranous wings. The female wasp has a completely black (metallic blue) head and body, with orange legs. At the end of the abdomen, a pointed projection is clearly visible, which is the sheath that protects a needle-like ovipositor. The male is the same colour but with an orange-brown band covering 4 segments of the abdomen. Larvae are creamy white, with a distinct black spike at the posterior end. The larvae are found in the sapwood in a tunnel that is tightly packed with frass behind the larva. Depending on the age of the larvae they can vary from a few millimetres to 3 cm in length. 

The fruiting bodies of the fungus has never been seen in South Africa. In Europe the fruiting bodies of Amylostereum areolatum resemble flat pieces of velvety leather stuck on the wood, sometimes with a protruding lip. The fruiting bodies have no pores and are grey to pinkish brown to burgundy red coloured.

Research into the visual and olfactory cues involved with Sirex noctilio mating and host location has confirmed the strong phototactic response of emerging wasps and identified putative pheromones, both of which might contribute to the mating swarms observed above the tree canopy. This understanding, together with optimization of plant volatile (kairomone) lures, will enable researchers to develop more effective monitoring tools.

On finding a host, the female wasp drills into the wood with her ovipositer and inserts a toxic mucous and its symbiotic fungus Amylostereum areolatum; it is a combination of the mucous and fungus that kills the tree. If the tree is suitable for infestation, the female will also deposit eggs into the wood. The fungus Amylostereum areolatum decays lignin and cellulose in wood, releasing carbohydrates that are pressed as a liquid from the wood and ingested by developing larvae. Bacteria could contribute to cellulose digestion and most likely fix nitrogen for the larvae. Nitrogen is also limiting for the fungus but could be obtained from bacteria or through parasitism of the nematode. Such parasitism can potentially affect nematode population levels in the tree. The larvae leave the fungal colonized area during pupation, possibly to avoid parasitism (Slippers et al. 2015). 

In South Africa, S. noctilio has a one-year life cycle. The adult flight season is from summer to early autumn, depending on the region. 

 

 

Silvicultural practices to increase vigour of trees, including thinning to remove the stressed and sub-dominant trees which are the primary host of S. noctilio. Biological control agents, namely the parasitic nematode Deladenus siricidicola and the parasitic wasp Ibalia leucospoides, have been released and can obtain high levels of parasitism.

1994
Western Cape, Eastern Cape, KwaZulu-Natal, Mpumalanga, Limpopo
Various pine species.
Eurasia, with the most common distribution in South-Western Europe.

Gallery

Fig 2
Sirex Life Cycle
Fig 1
Sirex Life Cycle
Fig 3
Sirex female laying eggs
Fig 4
Pine needles dying after Sirex attack
Fig 5
Pine trees killed by Sirex
Fig 6
Pine resin after Sirex attack
Fig 7
Sirex wasps around Jeff Garnas
Fig 8
Sirex noctilio wasps swarming above a wood pile
Fig 9
Sirex exit holes

Ryan K, Hurley BP. 2012. Life history and biology of Sirex noctilio. In The Sirex Woodwasp and its Fungal Symbiont: Research and Management of a Worldwide Invasive Pest. Springer.

Hurley BP, Slippers B, Wingfield MJ. 2007. A comparison of control results for the alien invasive woodwasp, Sirex noctilio, in the southern hemisphere. Agricultural and Forest Entomology 9:159–171.

Slippers B, Hurley BP, Wingfield MJ. 2015. Sirex Woodwasp: A model for evolving management paradigms of invasive forest pests. Annual Review of Entomology 60:601-619.

Slippers B, de Groot P, Wingfield MJ. 2012. The Sirex Woodwasp and its Fungal Symbiont: Research and Management of a Worldwide Invasive Pest. Springer.