Sirex Woodwasp
Sirex noctilio Fabricius
Integrated Pest Management for Commercial Horticulture
ipmnet.umd.edu
PEST ALERT - 2012
Introduction:
The Sirex woodwasp (SWW) is an exotic, invasive pest
considered one of the top 10 most serious forest insect
pests worldwide. SWW primarily attacks pine species. It
has no natural controls outside its native range, and
causes extensive losses in areas where it is accidentally
introduced. It is commonly detected in wood shipping
materials. The 2004 capture of a female in a field in
Oswego County, NY, was the first indication that an
established population existed in North America. With a
history of large scale damage and numerous pine species
attacked worldwide, SWW could wreak havoc to the
U.S. timber industry if it is not controlled.
U.S. Distribution/Spread:
SWW has been detected in New York, Pennsylvania,
Michigan, Vermont and the Canadian province of
Ontario. Based on its native range in Eurasia, SWW
could establish itself anywhere in North America where
pine occurs.
Adults are strong fliers and spread rapidly, moving about
25-30 miles per year. SWW larvae are easily transported
by people moving infested pallets, solid wood packing
materials, firewood or logs, with or without bark.
Host Plants:
The preferred hosts of SWW are pine species, especially
Scots, Red, and Eastern white pines in the US, and
widely reported in Monterey and loblolly pines
elsewhere. In its native range it attacks pines almost
exclusively, but in the U.S. it also attacks spruce, fir,
larch, and Douglas-fir.
Biology:
SWW usually produce one generation per year, but may
take up to two years to complete a generation in cooler
climates. The pests overwinter either as eggs or as larvae
deep within a tree. Adults emerge June-September, with
peak emergence in August. As adults emerge from trees,
they bore characteristic round exit holes that vary in
diameter depending on the size of the wasps. Females
Sirex adult female wasp
are attracted to stressed pine trees and can begin laying
eggs one day after emergence.
The biology of this family of woodwasps is a complex
interaction between the woodwasp, a symbiotic wooddecaying fungus, and the host tree. Female wasps drill
into the outer sapwood of a tree deposit a single egg.
Drill holes are usually located on the sunny side of trees,
are perfectly round, and may occur singly or in clusters
of 5 or 6 together. Females lay 25-450 eggs. Larvae
typically hatch after about nine days, but can remain
dormant for several months. As larvae grow, they bore
galleries deep into and through the wood. Mature larvae
pupate close to the bark surface, and adults emerge about
3 weeks later.
Female wasps usually pack the hole with spores of a
symbiotic fungus, Amylostereum areolatum. The
injected mucus makes a tree susceptible to the fungus,
which invades the vascular system and leads to tree
death. The fungus breaks down cellulose, creating
favorable conditions for egg hatch and providing food
for developing larvae.
Identification:
SWW are commonly called horntails because of the
horn-like projection on the last abdominal segment.
• Adults: large, robust, dark metallic blue/black
insects, 1.0-1.5” long (2.5-4.0 cm); some females
reach 1.8 inches (4.5 cm) including ovipositors.
• Adults have stout cylindrical bodies, pointed at the
tail tip, with a spear-shaped upturned horn (cornus)
on the last abdominal segment. (Woodwasps lack the
narrow "wasp-waist" characteristic of other wasps.)
• Females: head and body completely dark metallic
blue/black; legs orange; beneath the cornus on the
last abdominal segment there is a longer ovipositor
and sheath.
• Males: head and thorax dark metallic blue-black;
abdomen black at base and tail ends with middle
segments orange; front two pairs of legs orange,
hind pair black.
• Both sexes have black antennae typically over 0.8”
long (20 mm), and four clear yellow/orange
membranous wings.
• Eggs: sausage-shaped, creamy white, ~ 0.057” long
(1.46 mm) and ~ 0.01” wide (0.3 mm).
• Larvae: cylindrical, legless, creamy white grubs, up
to 1.18” long (30 mm), with a distinctive dark
“spike” (or spine) at the rear of the abdomen.
Infested pine displaying downward pointing needles
Larvae and damage to pine
Wood staining fungus carried by the wasp
•
What to Look For:
SWW prefer understory, rapidly growing, weak, injured,
diseased, or otherwise stressed living trees, and dead or
fallen trees. Trees with smaller diameters (< 6” or 16
cm) are more likely to be killed, but SWW readily
attacks larger trees that are damaged or stressed.
•
•
Symptoms of infestation include:
• Tree needles wilt and point straight down.
• Tree crowns turn light green to yellow to reddish
brown over 3-6 months.
• Resin beads or dribbles on the bark from
oviposition drilling wounds in year one.
• Drill holes are perfectly round, usually clustered
in groups of up to 5 or 6.
•
•
•
Drill sites are more common 10-30+ ft up (3-9+
m) on pole-sized and larger trees
Serpentine larval galleries tightly packed with
frass in the cambium. These may turn in toward
the heartwood then back out toward the bark
prior to pupation.
Larvae in cambial tissue beneath the bark, or
deep in drills.
Pupae are typically found within 2” (5 cm) of
the bark.
Round exit holes 1/8-3/8” in diameter (3-8 mm)
created by adults emerging in year two.
Fungal staining of the cambial layer beneath the
bark. Stains are long, narrow, oval shaped brown
bands along the grain, with drill hole(s) at the
center.
How to Report a Possible Sighting/Infestation
In Maryland: Maryland Home and Garden Information Center, University of Maryland: http://www.hgic.umd.edu/, or
call 1-800-342-2507 (outside MD: 1-410-342-2507).
Maryland Department of Agriculture: call 410-841-5920 to report suspect pests; visit http://www.mda.state.md.us/plantspests/invasive_species.php for information.
Nationally: USDA-Animal and Plant Health Inspection Service (APHIS):
http://www.aphis.usda.gov/services/report_pest_disease/report_pest_disease.shtml
Photo credits: adult female wasp (David R. Lance, USDA APHIS PPQ, Bugwood.org), larvae and damage (Vicky
Klasmer, Instituto Nacional de Tecnologia Agropecuaria, Bugwood.org), infested pine (Dennis Haugen, Bugwood.org),
and wood staining fungus (Dennis Haugen, Bugwood.org),
Sirex Woodwasp
By
Mary Kay Malinoski, Extension Specialist in Entomology,
University of Maryland Extension, mkmal@umd.edu
David l. Clement, Extension Specialist in Plant Pathology,
University of Maryland Extension, clement@umd.edu
The information given herein is supplied with the understanding that no discrimination is intended
and no endorsement by University of Maryland Extension is implied. Read labels carefully before applying any
pesticides.
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