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University
of Rhode Island GreenShare Factsheets
Pine
Sawflies
Neodipron lecontei (Fitch)
& N. sertifer (Geoffroy)
Hymenoptera: Diprionidae
The two most common species of pine sawflies which occur
in Rhode Island are the redheaded pine sawfly and the European
pine sawfly. The redheaded pine sawfly occurs from S.E. Canada
throughout the eastern U.S, and is the most widespread and
destructive of the pine sawflies. Feeding is primarily restricted
to the two- and three-needled pines, such as Jack, red, shortleaf,
loblolly, slash, longleaf and pitch pines. White pine and Norway
spruce may also be defoliated by the redheaded sawfly.
The European pine sawfly, which was accidentally introduced
from Europe, is common from southwestern Ontario through New
England and west to Iowa. The European pine sawfly is the most
common sawfly in ornamental nurseries and Christmas tree plantations.
In landscape situations, this sawfly prefers mugho and table
top pines. However, it readily attacks Scotch, red, Jack and
Japanese pines as well. It will rarely feed on white, Austrian,
Ponderosa, shortleaf and pitch pines, especially if these are
intermixed with the preferred hosts.
Sawfly adults look similar to true
flies, yet have two pair of wings instead of one pair. Sawfly
larvae resemble caterpillars,
yet have at least six pairs of "stublike" prolegs behind the
three pairs of true legs on the insect's abdomen (caterpillars
never have more than five pairs of prolegs).
Redheaded pine sawfly: Adult females are 6 to 9.5
mm (1/4 to 3/8 inch) in length while males are 5 to 6.5 mm
(1/5 to 1/4 inch) long. Males are completely black except for
their legs and wings, and females are predominantly black with
a whitish underside of the abdomen. Redheaded pine sawfly eggs
are oval, 0.5 mm (1/32 inch) long and 0.25 mm (1/64 inch) wide.
They are laid individually in a row of slits cut into the edge
of the needles. All eggs laid by a female are generally grouped
on needles of a single twig. Larvae emerge from eggs 2 to 5
mm (1/16 to 1/5 inch) long. After feeding, the larval body
develops black spots and the head capsule becomes orange-red.
In the fourth and fifth instars, black spots surround the eyes
and the body is deep-yellow. The larvae spin cocoons to overwinter
and pupate in. The cocoons are red-brown, cylindrical with
rounded ends, and are 10 mm (../images/8 inch) long for females
and 7.5 mm (5/16 inch) long for males.
There are two to three generations/year. The redheaded
pine sawfly overwinters in the prepupal stage in its cocoon
spun in the litter of the soil beneath the infested trees.
Pupation occurs soon after the onset of spring warm weather,
and adults emerge in a few weeks. Eggs deposited in the needles
hatch in three to five weeks. Larvae feed gregariously on new
and old needles and also on the tender bark of young twigs.
Larvae begin spinning cocoons in late June or early July. Second
generation adults emerge in July and August. Larvae feed through
September and then spin their cocoons. In warmer areas, adults
will emerge at the end of September to late October and lay
eggs for a third generation that remains active into December.
European pine sawfly: Usually only one generation
occurs and the winter is spent as an egg inserted into slits
along the edge of needles. The eggs hatch in April through
mid-May and the larvae may feed until mid-June. The caterpillar-like
larvae are grayish-green and have a light stripe down the back
and a light stripe along each side followed by a dark green
stripe. Fully grown larvae are about 25 mm (1 inch) long. The
larvae feed in groups or colonies, often with three or four
feeding together on a single needle. Distributed larvae raise
their heads and tails in a threatening manner. Mature larvae
drop to the ground and spin tough, brown cocoons in the duff.
A few larvae may pupate on the tree. The adults emerge in late
August through September to mate and lay eggs. Each female
lays six to eight eggs in a single needle and 10 to 12 needles
are used. These eggs can be located after a hard frost turns
the egg laying scar yellow.
Pine sawflies usually feed on young trees, preferably
0.3 to 4.6 m (1 to 14 feet) tall. Trees growing under stress
in shallow soils, very wet or dry sites, or under stress from
competing vegetation are especially susceptible to infestation
and heavy defoliation. Outbreaks occur periodically and tend
to subside after a few years of heavy defoliation. Severe outbreaks
have resulted in death or deformity of young pines.
The first instar larvae (the ones
hatching from the egg) can only eat the needle surface, causing
the needles to turn
brown and wilt, giving a straw-like appearance to the needles.
As the larvae grow, they remain together and feed from the
tip of a needle to the base. The larvae feed on older foliage
and move from branch to branch as they strip the needles. Trees
which are entirely defoliated are severely stunted, but since
the new growth is rarely attacked, the trees will survive.
Larvae will often migrate to new trees if the needles on their
current host have been devoured. Heavily infested trees end
up with a "bottle brush" effect--all the old needles are missing
and only the current year's needles are present.
Numerous natural control agents play important roles
in keeping redheaded pine sawfly populations down. Outbreaks
often collapse from rodents feeding on the pupae and diseases
killing the larvae. Of the 58 species of parasitic and predatory
insects affecting this pest, the native egg parasite Closterocerus
cinctipennis Ashmead (Hymenoptera) and the larval parasite Spathimeigenia spp.
(Diptera) are the most important.
Best controls are obtained when the larvae are still
small, so look for the straw-like needles left behind by the
young larvae. Inspections should be made in late April and
early May. The egg laying scars can also be seen by inspecting
the needles in late winter.
Cultural Control:
• Remove competing vegetation
before planting pines.
• Avoid planting pines in
high hazard areas such as frost pockets, or on excessively
dry, wet or nutrient-deficient
soils.
• Promote early closure of
pines to prevent competing vegetation such as weeds or hardwoods.
Mechanical Control:
• Egg Removal - If the needles
containing overwintered eggs can be found before they hatch,
they can be pulled off
the plants and destroyed. Do not simply throw them on the ground,
as the eggs can still hatch.
•Colonies of larvae can be
easily removed by clipping off the infested branch. Place
these branches in a plastic
bag and destroy. Colonies can also be knocked off by sharply
striking the infested branch. Crush the larvae or knock them
into a pail of soapy water. If few colonies are present, they
can be controlled using these methods, but large infestations
are better controlled by general spraying.
Insecticides:
When deemed necessary, chemical
treatments can be used as an effective control. Several horticultural
oils (often
called "summer" or "verdant" oils) and insecticidal soaps are
labeled for control of sawflies on ornamentals. These usually
work well when the sawfly larvae are small and thorough coverage
of the colony can be achieved.
Adapted from the Virginia
Cooperative Extension and the Ohio State University Extension,
1999
Pesticides
are poisonous! Read and follow all safety precautions on labels.
Handle carefully and store in original containers out of reach
of children, pets or livestock. Dispose of empty containers
immediately, in a safe manner and place. Pesticides should never
be stored with foods or in areas where people eat.
When trade names are used for identification, no product endorsement
is implied, nor is discrimination intended against similar materials.
Be sure that the pesticide you intend to use is registered for
the state of use.
The user of this information assumes all risk for personal injury
or property damage.
For more
information, call the URI CE Gardening and Food Safety Hotline
at 1-800-448-1011 or (401)874-2929 from outside Rhode Island;
Monday-Thursday between 9 am and 2 pm.
University
of Rhode Island Cooperative Extension provides equal program
opportunities.
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