Sirex woodwasp (Sirex noctilio) is a large robust wasp, or horntail, that is native to Europe, Asia, and northern Africa—where it is generally considered to be a secondary pest. The first North American discovery of S. noctilio was in 2004 in Fulton, NY. SW attacks pine tree species (Scotch, Monterey, Loblolly, Ponderosa etc.) Unlike native woodwasps that attack dead and dying trees, SW target living pines that have been stressed, suppressed or injured—stress caused by drought-induced overcrowding have been known to be common host trees.
Due to the fact that sirex woodwasp larvae are hidden deep within host trees, S. noctilio can be unintentionally introduced through the transportation of infested wood materials. Pine trees are often used to make solid wood packing material, and since the life cycle of sirex woodwasps takes a year or more, insects can easily be transported in pallets or other wood packing material undetected. Due to its native range in Europe and Asia, S. noctilio could establish itself where pines occur in any climate zone of North America. All pine species are believed to be at risk, particularly stressed Scotch pine and red pine, as well as, eastern white pine.
Listed as one of the top 10 most serious forest insect pest invaders worldwide, S. noctilio has caused extensive losses to (non-native) pine plantations across the Southern Hemisphere, in Australia, New Zealand, Chile and South Africa. However, all pine species are believed to be at risk, particularly stressed Scotch pine, red pine and eastern white pine. Literature indicates that native softwood species are also at risk. With an estimated 8 billion US annual value, pine species in the Southern US region are of great national concern— as pine resources in southern regions are often grown in large homogeneous commercial plantations making them more susceptible to infestation.
The most noticeable symptom of a sirex woodwasp infestation is a condition called chlorosis, in which leaves produce insufficient chlorophyll; lack of chlorophyll cause leaves to turn pale yellow or yellow-white. Chlorosis is caused by the toxic mucus injected by female sirex woodwasps and begins in the crown of host trees (where ovipositor injection generally occurs (mid-bole, about 10-30 ft. up). Between 3-6 months after infestation, foliage begins to wilt and change color from dark green to lighter shades of greenish-yellow and eventually to red.
The photo below shows the damage done by the sirex woodwasp at a South Australian pine plantation; although the resolution may not be very clear, note the large stands of pine trees displaying symptoms of chlorosis.
Another sign of a sirex woodwasp infestation is white resin dripped along the bark at egg-laying sites; and large round holes that have been bored through the bark by adult S. noctilio that emerge to begin their search for new host trees, this usually occurs in July.
Adults are usually 1-1.5’’ long and have dark metallic blue/black bodies with reddish-orange segments and a spear-shaped plate (cornus) at the tail end; with reddish-yellow legs, black feet and black antennae.
Males’ abdomens are black at the base and tail end with orange middle segments.
Females have a long ovipositor under their cornus.
Larvae are creamy white, legless and have distinctive dark spines at the rear of their abdomens. Pupae formed in the outer layers of sapwood are initially creamy-white and gradually assume the color of adults.
Biology: Throughout most of the US, S. noctilio completes one generation per year. Adult emergence occurs throughout July to September—peak emergence occurs during August. Female S. noctilio lay from 25-450 eggs depending upon the size of the female. Unfertilized eggs develop into males, whereas, females are produced from fertilized eggs. Larval stages vary from 6-12 and each stage takes generally 10-11 months. Pupation of mature larvae occurs close to the bark surface, in which adult S. noctilio emerge about 3 weeks after pupation.
The parasitic nematode, Deladenus siricidicola is the key biological control agent used to control sirex woodwasps. D. siricicidicola infects sirex woodwasp larvae, and ultimately sterilizes adult females. The way in which this parasitic nematode attacks sirex woodwasps is quite interesting. There are two morphological forms that D. siricicidicola inhabits—a fungal feeding form and a parasitic form.
The fungal feeding form of D. siricicidicola lives in the pine tree and eats the symbiotic fungus (A. areolatum) injected into the tree by adult a S. noctilio female. During fungal feeding stages, parasitic nematodes reproduce for many generations in the absence of sirex woodwasps.
However, if S. noctilio larvae are detected, the fungal feeding form of the nematode transforms into parasitic Deladenus siricidicola adults. These infective adults inject female S. noctilio with juvenile D. siricicidicola, which migrates into the reproductive organs of the host infecting their eggs. The infected S. noctilio female is not killed by this parasitic process, instead “parasitic castration,” a parasitic strategy that blocks the reproduction of its host, takes place; after parasitic castration takes place, a parasitized female S. noctilio continues through their life cycle, but their eggs contain the larvae of D. siricicidicol—cleverly tricking females to inject the parasitic nematode into host trees instead of their own larvae. Once D. siricicidicola is injected by a female sirex woodwasp host, it returns back into it’s’ “fungal feeding form” until the cycle begins anew.
Fungal feeding form of D. siricicidicola
Title Photo: sirex woodwasp: en.wikipedia.org. Symptoms photos and male/female sirex photo: Dennis A. Haugen & Kent Loeffler, dept. of Plant Pathology Cornell University, (bugwood.org). Larvae photo: Bernard Slippers, FABI University of Pretoria. Biological control photos: E. Erin Morris, (Cornell.edu).
Haugen, Dennis A., and E. Richard Hoebeke. “Pest Alert – Sirex Woodwasp—Sirex Noctilio F. (Hymenoptera: Siricidae).” Pest Alert – Sirex Woodwasp—Sirex Noctilio F. (Hymenoptera: Siricidae). USDA Forest Service, n.d. Web. 10 July 2015. <http://na.fs.fed.us/spfo/pubs/pest_al/sirex_woodwasp/sirex_woodwasp.htm>.
“Sirex Woodwasp Sirex Woodwasp – Sirex Noctilio.” Sirex Woodwasp. New York State Department of Environmental Conservation, 2015. Web. 10 July 2015. <http://www.dec.ny.gov/animals/7248.html>.
*For information on biological control for sirex woodwasp view:
“Nematode Parasite of Sirex.” New Zealand Farm Forestry Association, n.d. Web. 10 July 2015. http://www.nzffa.org.nz/farm-forestry-model/the-essentials/forest-health-pests-and-diseases/Pests/Sirex-noctilio/Deladenus-Ent48
Elizabeth Erin Morris. “Deladenus Siricidicola.” Deladenus Siricidicola. Cornell University, n.d. Web. 15 July 2015. <http://www.biocontrol.entomology.cornell.edu/pathogens/Deladenus.php>.
Gartner, Steve. “Sirex Wasp Eradication – CSIROpedia – CSIROpedia.” Sirex Wasp Eradication – CSIROpedia – CSIROpedia. N.p., 5 Sept. 2014. Web. 10 July 2015. <http://www.csiropedia.csiro.au/display/CSIROpedia/Sirex+wasp+eradication>.
*If you think you have found sirex woodwasp, take a photo and email it to the Forest Health team or call (866) 640-0652. Keep the insect in a container in your freezer in case it is sirex woodwasp. It will need to be confirmed by a lab.