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
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.
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).
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.
pine sawfly larva (R.Harrison)
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
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.
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.
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.
competing vegetation before planting pines.
planting pines in high hazard areas such as frost pockets, or on
excessively dry, wet or nutrient-deficient soils.
early closure of pines to prevent competing vegetation such as weeds
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.
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.
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.
from the Virginia Cooperative Extension and the Ohio State University