Sirex noctilio, or the sirex wood wasp, is native to Europe, North Africa, and Northeast Asia. It was first detected in a funnel trap in Fulton, NY in 2004 as a part of a USDA Cooperative Agricultural Pest Survey (CAPS) that was mainly surveying for exotic bark beetles. The funnel trap was baited with cis-verbenol, ipsdienol, and methyl butenol and placed 9.94 miles from the port of Oswego on Lake Ontario (Hajek et al., 2021). Since then, Sirex noctilio has been found in at least 9 US states and 2 Canadian provinces (New York, Pennsylvania, Vermont, Connecticut, Ohio, Michigan, New Jersey, Massachusetts, and New Hampshire; Ontario and Quebec). The sirex wood wasp was first detected in Massachusetts in 2014 in Hampden County (Hajek, Personal Communication). During the growing season (roughly from July - September, but in some cases as early as June), adult female sirex wood wasps will lay their eggs in stressed or weakened host plants. At that time, they also deposit into the tree a mutualistic fungus as well as venom. At the egg laying site, trees may respond by secreting resin. Eggs hatch in 16-28 days. The larvae (immatures) take at least a year to develop, tunneling in the sapwood of the xylem. 6-12 larval instars occur. Larvae are creamy white in color, cylindrical in shape, and up to 1.25 inches long. Larvae also possess a dark spine or point at the end of their abdomen. Following pupation, adults chew their way out of the host plant through the bark, leaving round exit holes of variable sizes. The size of the adult wasp is highly variable, with length varying from 0.24-1.46 inches. Females tend to be larger than males. Larger females are capable of carrying more eggs. Eggs found within females of varying sizes have ranged from 5 to over 280 eggs. Females are metallic blue (head and thorax and abdomen) with orange legs. Males also have a metallic blue head and thorax, but the center of the abdomen is orange with black at the rear end. Males have black legs, with thicker hind legs. Adults have a lifespan of approximately 1-2 weeks. Adults use that time to focus on locating mates, mating, dispersing, and egg laying. Females can lay unfertilized eggs which will develop into males.
Female sirex wood wasps lay their eggs primarily in stressed or weakened pines, where they also deposit a mutualist fungus, Amylostereum areolatum, and venom gland secretions. This venom reduces tree vascular function and, in combination with the mutualistic nutritional fungus, initiates the process of tree death. The fungus needs the venom to weaken the tree in order to become established. The stress from the venom causes needle chlorosis and wilt. Tree mortality then occurs over time as the sirex wood wasp larvae hatch and develop in the tree (Hajek et al., 2021). The larvae need the fungus to decompose the wood of their host so they can feed on it.
Male aggregation pheromones of the sirex wood wasp have been isolated and determined to attract adults of both sexes. Adult sirex wood wasps are also attracted to light. Black flight intercept panel traps baited with host plant volatile chemicals (monoterpenes) have been used in monitoring programs for the sirex wood wasp. Research has shown that panel traps are more effective at capturing the sirex wood wasp than funnel traps. Limited research is available regarding the most effective height at which to hang traps. Some research suggests that male sirex wood wasps may fly higher than females; however, if male sirex wood wasps were stuck to sticky mesh traps, females would fly higher in response to the presence of the males (Martinez et al., 2014).
The silvicultural management of the sirex wood wasp will not be discussed in great detail here except to note that proper thinning and maintenance of stand vigor is necessary to help reduce the potential impact of this insect. In forested stands, the sirex wood wasp has the most success in infesting overstocked, unmanaged Scots (Pinus sylvestris) or red pine (P. resinosa) stands on poor growing sites. Even in stands where proper thinning and maintenance aren't provided, the sirex wood wasp preferentially attacks suppressed, smaller and shaded, or injured trees.
The host plants themselves of the sirex wood wasp play a large role in suppressing their populations. They do this by flooding egg laying sites with resin and defensive polyphenols (compounds), some of which have antifungal properties. It is thought that the polyphenols are able to restrict the growth of the sirex wood wasp larvae as well as Amylostereum areolatum (Coutts and Dolezal, 1966; Hillis and Inoue, 1968).
Landscape specimen trees, especially Scots pine, should be planted on appropriate sites and cared for to promote tree vigor. Reducing the impact of abiotic and additional biotic stressors will reduce the suitability of the tree as a host for the sirex wood wasp.
Important natural enemies include several native hymenopteran parasitoids that may kill up to 25% of the sirex wood wasp larvae in North America. These include Ibalia leucospoides, Rhyssa persuasoria, R. lineolata, and Megarhyssa nortoni. Each of these parasitoids are solitary, meaning that a single sirex wood wasp that is parasitized will allow for the development of a single parasitic wasp. The parasitic nematode, Deladenus siricidicola, was introduced into North America with invading S. noctilio, but has little impact on sirex wood wasp populations. In North America, the nematode does not at this time sterilize adult sirex wood wasps (Hajek et al., 2021). Woodpeckers may be predators of Sirex noctilio, however their impact on the insect may be variable and not reliable as a source of population reduction. More research is needed. Woodpecker feeding on the trunk of infested host plants can be a useful tool in identifying potentially infected hosts in the field.
Entomopathogenic nematodes (L)
Products registered in Massachusetts do not currently have labeling specific to Sirex noctilio. Contact the MA Department of Agricultural Resources Pesticide Program for more information.
Make insecticide applications after bloom to protect pollinators. Applications at times of the day and temperatures when pollinators are less likely to be active can also reduce the risk of impacting their populations.
Note: Beginning July 1, 2022, neonicotinoid insecticides are classified as state restricted use for use on tree and shrub insect pests in Massachusetts. For more information, visit the MA Department of Agricultural Resources Pesticide Program.
