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Shelterbelt Centre Pest Leaflets
Forest Tent Caterpillar
Hosts: Trembling aspen, poplar and other trees and shrubs.
Appearance and Life
History: Larvae emerge from
egg bands in the spring, just as
the foliage begins to appear on
the trees. Larvae are dark
brown with broad blue bands
along each side and marked
with a row of white key-hole
shaped markings down the
centre of the back. Contrary to
their name, forest tent
caterpillars do not construct a
tent, but feed openly on the
foliage. By mid to late June,
the full grown larvae are 45 to
55 mm in length. The moths
are present from mid-July to
early August. After mating, the
females deposit egg bands
containing 100 to 200 eggs on
twigs of host trees. The egg
bands are 10 to 20 mm long
and are covered with a foamy,
dark-coloured, protective sub
stance. The forest tent
caterpillar completes one
generation a year.
Damage: Forest tent
caterpillar damage can range
from a thinning of the crown to
complete defoliation. After a
severe attack most trees will
refoliate the same year. Trees
may suffer top dieback or die
if defoliated three or more
consecutive years.
Control: Natural factors such
as disease, parasites,
predators, starvation and
adverse weather usually keep
populations low. Where
practical, some control can be
achieved by removing the egg
bands from the host trees late
in the fall or early spring. For
large shelterbelts, the larval
stage may be sprayed with an
insecticide such as malathion,
acephate, carbaryl,
deltamethrin, or Bacillus
thuringiensis. Malathion,
deltamethrin, and Bacillus
thuringiensis are also
registered for aerial
application. Application of
insecticides should be
conducted in late May to early
June while larvae are small
and damage is light. Spraying
will probably be required if
the number of egg bands on the
tree is greater than the trunk
diameter in centimeters,
measured at approximately 1.5
m above ground level.
For more information contact:
PFRA Shelterbelt Centre
Indian Head, Sask. S0G 2K0
Phone: (306) 695-2284 or Fax: (306) 695-2568
E-mail: pfratree@agr.gc.ca
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