Sirex noctilio, known as the Midnight woodwasp, European woodwasp, European horntail woodwasp, or sirex woodwasp, is a species of woodwasp, native to Europe, Asia, and northern Africa.New York State Department of Environmental Conservation, Copyright © 2011. Sirex Woodwasp – Sirex noctilio. http://www.dec.ny.gov/animals/7248.html Adults vary in length from .
This woodwasp is an invasive species in many parts of the world, including Australia, New Zealand, North America, South America, and South Africa, where it has become a significant economic pest of pine trees. The wasp can attack a wide variety of pine species, although some species seem to be more susceptible than others, and stressed trees often are attacked.
During oviposition, the female wasp lays two eggs with or without a mucoid substance and a symbiotic fungus for the larvae to feed on once they hatch. The mucoid substance is toxic to trees and aids in tree decline. The arthrospores from the symbiotic fungus, Amylostereum areolatum, are also pathogenic.
Characteristics
Adult
The European woodwasp has a sturdy, cylindrical body without a waist, but with a pointed abdomen. The female body is , and the male is long. Both sexes have long, black, bristle-shaped antennae, which are rather close together.Sirex noctilio (Fabricius) – Sirex woodwasp. Canadian Food Inspection Agency, www.inspection.gc.ca.B. Långström et al: Non-Coleopteran Insects. In: François Lieutier: Bark and Wood Boring Insects in Living Trees in Europe: A Synthesis. Springer, 2004. , pp. 530–531.
The body of the male is black, except for the orange middle part of the abdomen. The wings are yellowish-translucent and the antennae are black. The front pair of legs have a yellowish-orange colour, the back pair is heavily thickened and is coloured black on the posterior splint and tarsus, while the femur is orange.
The females are iron blue, and have orange legs and black antennae. This is a notable distinction from S. juvencus, which has red antennae. The females also have yellowish wings, though browner than the male's wings. The ovipositor is below the tapering tip of the abdomen, and is strengthened with zinc to aid drilling into wood. The sting is connected with the mycetangia, which are special organs on the abdomen, where the female stores the oidiae (asexual fungus spores), from broken segments of hyphae. These spores are deposited, together with the eggs, in the host tree wood to germinate. Both larvae and adults have strong mandibles and can drill through lead plates.
Larva The larvae of the European woodwasp are almost colourless and only have three stub-shaped pairs of sterna. They cut through host wood with their powerful mandibles. They have a pointed, dark tip at their rear end, which presses the drilling dust on the walls of the borehole. They closely resemble other larvae in the genus Sirex.Uwe Sedlag: Insekten Mitteleuropas. dtv, 1986. , pp. 244–245. A detailed description of the larva of this species was first given in 2021.
Native and introduced range
The native habitat of the European woodwasp is the temperate Palearctic realm, ranging from Maghreb in northwest Africa, throughout Europe, and across Asia in Siberia and Mongolia to the Kamchatka Peninsula. They live in deep pine-rich forests.
The species has reached other continents, such as Australia, South Africa and North America, through the export of timber and firewood. While invasion was prevented in North America for a long time, the European woodwasp established itself in New Zealand around 1900. There, it contributed to massive pine declines in the first half of the 20th century, spreading to Tasmania in the 1950s and then to the Australian mainland. Since 1980, it has reached pine plantations in Uruguay, and later also Argentina, Brazil and Chile; it was found in South Africa in 1994. The population increased in the Great Lakes area from 2004 on; the species had reached Vermont, New York, Pennsylvania, Ohio, and Michigan by 2009.Jamie Perrie: Sirex noctilio Positive Counties per Year. USDA/APHIS/PPQ, 20 October 2009. The woodwasps can swarm between ; it has been estimated it will take until about 2050 to spread to the far southeast of the USA at the current rate of spread.Chalkley, D. Diagnostic Fact Sheet for Amylostereum areolatum. Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved on 1 March 2010.Economic Analysis of the Potential Impact of Sirex noctilio, with Emphasis on Pines in the Southeastern United States. USDA Forest Service, Arlington 2006.
Subsequently, forestry authorities intensified their pest control methods and additionally started education campaigns, such as warning not to transport firewood over large distances or to store it too long. Through wood export, the wasp was able to spread to East Asia, West Australia and parts of Africa. Remote locations, such as the Horn of Africa, may be spared from the European woodwasp, providing the area is controlled. The Invasive Species Specialist Group (ISSG) of the IUCN has graded the wasp as heavily invasive.Sirex noctilio in the Global Invasive Species Database of the IUCN. www.issg.org, 23 November 2009. Retrieved on 22 August 2010.
Ecology
Phenology The flight time of the adults or imagines begins in the late summer to early autumn, but the date depends on the region and climate. The males hatch out earlier than females and create swarms which gather around the treetops. The females seek out leks and couple with the males on the uppermost shoots. Then the females search for suitable host trees, if possible choosing weak and dry wood. They orient on monoterpene hydrocarbon compounds, which weakened trees produce. When a tree is stressed through dryness or exterior injuries, the compounds pervade osmotic barriers and escape from the bark.
The female alights on the bark to drill several holes through the wood to the xylem, placing one egg in each. At the same time, she inserts spores of Amylostereum areolatum and a phytotoxic secretion. The holes branch out into several tubes, which lead away radially. The eggs are white, sausage-shaped, and by in size. Small females may lay 20 eggs, while the largest can lay up to 500. Sometimes, eggs are not placed in every tube. In the last tube, the female injects only the secretion and the fungal spores. The females often die after just three or four days, sometimes even during oviposition (egg-laying), through overexertion.Proposed Program for Management of the Woodwasp Sirex noctilio Fabricus (Hymenoptera: Siricidae). United States Department of Agriculture, 2007.Eichhorn, O. Siricoidea. In: Wolfgang Schwenke: Die Forstschädlinge Europas. Band 4: Hautflügler und Zweiflügler. Hamburg 1982. , p. 215.
Development of larvae Larvae of European woodwasp develop through arrhenotoky, in which male larvae develop only from unfertilised eggs, the females only from fertilised ones. Usually, 10 males are produced per female, but the ratio varies between 20:1 and 1:1. The larvae hatch after eight days at the earliest, but in some exterior conditions, they may remain in the egg for several months. At the optimal temperature of around , they hatch out after 10 to 12 days. Although the larvae hatch at two to three days earlier, they are 20% more likely to die. Such extreme temperatures result in slower development, and below , the larvae die. A sufficient interspersion of the wood with the mycelium of the woodwasp is crucial for its hatching, as the fungus prevents the wood from drying out. Without these prerequisites, hatching is not possible. The tree can only ward off the infestation if it floods the boreholes with resin or halts the fungus by producing a wall of polyphenols.
Six to twelve larval stages occur. During the first two stages, the larvae live off surrounding fungal tissue, until they reach the inner wood. Up to the fourth stage, they eat through the final summer wood along the tracheids, and finally towards the heartwood. After the seventh stage, they usually reach their maximum size. While penetrating further, they normally turn either up or down, but they turn back if they meet a foreign borehole, encounter bubbles of resin, or dry out. The larvae only live off the fungal mycelium, which they digest through a secretion. They pupate several centimetres under the bark. Before this, female larvae sequester a secretion containing fungal oidia, which adult females incorporate in their mycetangia above their ovipositors. The adults eat through the bark, but, depending on the weather, they remain in the hatch hole for up to three weeks before they leave the wood in warm and sunny weather.Morgan 1968, p. 242.
The period from hatching to pupation lasts 10 days to two years, exceptionally up to six years. Climate is a major factor, because development is slower in colder regions.
Symbiosis
The European woodwasp and Amylostereum areolatum have a mutualistic symbiotic relationship. The European woodwasp is, together with S. juvencus and S. nitobei from eastern Asia, one of three symbionts of the fungus that in the first instance benefits from its vector function. Additionally, the wasp creates the optimal conditions for the infestation through the fungus by drilling into the underlying wood layers and weakening the host tree. The fungus has adapted to this process in the course of evolution and only rarely creates fruit bodies.Hudson, Harry J.: Fungal Biology. CUP Archive, 1992. , pp. 248–252.
Conversely, the woodwasp is fully dependent on the symbionts. Decomposition enables the larvae to unlock the wood by producing white rot. The mycetangia of this and other wasps from the family Siricidae support a close relationship with saprobiontic fungi. Without the process of decomposition of the host tree and weakening of the infested tree, the development of larvae is arrested. If the tree can recover from the consequences of the wasp secretion, it blocks the boreholes with resin, thus killing the larvae.
Host spectrum The European woodwasp only attacks conifers, especially pines. In its usual habitat, these are mainly Pinus sylvestris, P. pinaster and P. nigra. In the Southern Hemisphere and in North America, the wasp attacks exotic and domestic pine species, generally in plantations. Examples include P. radiata and P. taeda in the United States.
Unlike any other species of Siricidae, the European woodwasp can damage relatively healthy trees so heavily, they die back. However, the wasp mainly infests weakened trees; only when the population is high does the insect also attack intact and healthy trees. Because the wasp larvae and the fungus need living wood, the European woodwasp does not infest dry or dead timber. However, wasps may hatch from processed wood which was already infested.
Pines in North America that have been attacked or confirmed as hosts are: Scots (Pinus sylvestris), Monterey (P. radiata), loblolly (P. taeda), slash (P. elliottii), shortleaf (P. echinata), ponderosa (P. ponderosa), lodgepole (P. contorta), and jack (P. banksiana) (Haugen 1999).Haugen, D.A. (1999) Sirex noctilio. Pest Reports – EXFOR Database . Retrieved on November 25, 2012 By the spring of 2011, S. noctilio had been found in Michigan, Pennsylvania, New York, and Vermont.
Though pines are preferred, it has also been recorded attacking other genera in the Pinaceae, including Picea (spruces), Abies (firs), Pseudotsuga (douglas-firs), and Larix (larches).
Symptoms of infestation
Infestation damage can be divided into four categories or phases, depending on whether it is caused by the imago, fungus, larvae or secondary parasites.