Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
European Pine Sawfly
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The
European pine sawfly is the most common sawfly found infesting pines in
landscapes, ornamental nurseries and Christmas tree plantations. Sawfly
larvae look like caterpillars but they are the larvae of primitive wasp-like
insects. They are common from southwestern Ontario through New England and
west to Iowa. This pest was accidentally introduced from Europe. Plants Attacked In
the landscape, this pest prefers Mugho and table top pines. However it
readily attacks Scotch, red, Jack, and Japanese pines. It will rarely feed on
white, Austrian, Ponderosa, shortleaf and pitch pines, especially if these
are intermixed with the preferred hosts. |
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Damage The
first instar larvae (the ones hatching from the
egg) can only eat the needle surface which causes the needles to turn brown
and wilt, appearing straw-like. 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. That is, all the old needles
are missing and only the current year's needles are present. |
Description and Life Cycle
Usually
only one generation occurs and the winter is spent as an egg inserted into
slits along the edge of needles. The eggs hatched 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, a light stripe along each
side followed by a dark green stripe. Full grown larvae are about one 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.
Control Hints
Best
control is 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.
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Strategy 1: Natural Controls - Several parasites have been
introduced to control this pest and native birds feed on the larvae. Rodents
often eat the pupae in the soil. These agents are usually not adequate in
urban settings. Strategy 2: Cultural Mechanical
Control- Egg Removal- If the needles containing over wintered eggs can be found before
they hatch, they can be pulled off the plants and destroyed. Do not simply
throw on the ground since the eggs can still hatch. |
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Strategy 3: Cultural/Mechanical
Control - Larval Destruction - 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 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.
Strategy 4: Chemical Control -
Spot Sprays of Insecticides - Many aerosol or hose end sprayable
insecticides are available for spraying of colonies. This is usually adequate
for most home landscapes.
Strategy 5: Chemical Control -
General Insecticide Spraying - This sawfly rarely infests large acreages unless
controls have not been used for several seasons. General sprays may be warranted
if more than 25% of the trees are infested.
Information obtained through the Ohio State Extension Factsheet HYG-2055-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES