Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES
Redheaded Pine Sawfly
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There
are several species of sawflies that attack pines in Ohio, but the redheaded
pine sawfly, can be especially troublesome. Because it has two generations
per year, all the needles on a pine can be eaten in a single season. The
spring generation can strip trees of their older needles and the summer
generation can strip off the current year's needles. This total defoliation
can result in death of the pine. This sawfly is found from Southeastern
Canada through the eastern United States. |
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Plants Attacked
Redheaded
pine sawflies prefer two and three needled pines including: Scotch, jack,
shortleaf, loblolly, slash, red, Mugho. It has also been rarely found feeding
on white pine, Norway spruce, Deodar cedar and larch, especially if near its
preferred pine hosts.
Damage
The
first instars (newly hatched) larvae strip the needle surface leaving straw-like
remains. Larger larvae eat the entire needle down to the sheath. The larvae are
strongly gregarious, feeding in groups of 100 or more. Usually one year old
foliage is eaten but all foliage may be eaten on heavily infested plants. If a
tree is entirely defoliated before the larvae are mature, they will migrate to
the nearest conifer. This is when they may attack non-preferred hosts. Severe
defoliation may kill plants while light defoliation will result in unsightly
trees.
Description and Life Cycle
This pest over winters as a pre-pupa (fully mature
larva), in a cocoon in the duff under host trees. When spring arrives, the pupa is
formed and the wasp-like adults emerge in a few weeks. Some pre-pupae have been
known to remain dormant for two to three seasons before pupating. Females find
preferred pines and deposit over 100 eggs in rows of slits along the edges of
needles. Unmated females can still lay eggs but the offspring will all be
males. Only fertilized females can produce more females.
The eggs
hatch in about a month into caterpillar-like larvae. The young larvae only eat
the surface of needles resulting in thin straw-like brown remains. Older larvae
strip all the foliage down to the branch and can even gnaw on the branches if
nothing else is available. The larvae take about one month to mature into one
inch long, yellow bodied insects with black spots and orange-red heads. Mature
larvae drop to the duff and pupate. From New York north, this insect has only
one generation. South of this line, there are usually two generations and south
of South Carolina, three generations are found.
Control Hints
Best
control is obtained when the larvae are still small, so look for the needles
with rows of spots which indicate egg lying, or look for the straw-like needles
left by the young larvae feeding. Remember that some pre-pupae remain dormant
for two seasons so elimination of active larvae in one season does not
guarantee that the larvae will not be back for a second generation or the next
year.
Strategy 1: Natural Controls - Several parasites, birds and
viral diseases kill the larvae. Rodents often feed on the pre-pupae and pupae
in the duff. These agents are sufficient in natural stands of pines but are not
adequate in most urban areas.
Strategy 2: Cultural/Mechanical
Control -
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 3: 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 4: 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-2054-95
Insect
and Disease Fact Sheet Compliments of New Century
1-877-79TREES