Extension Communications
3614 Administrative Services Building
Ames, Iowa 50011-3614
(515) 294-9915
3/24/03
Contacts:
Mark Shour, Entomology, (515) 294-5963, mshour@iastate.edu
Jean McGuire, Continuing Education and Communication Services, (515) 294-7033,
jmcguire@iastate.edu
Yard and Garden Column for the Week Beginning March 28, 2003
European Pine Sawfly, an Early Season Pest
By Mark Shour
Extension Entomologist
Iowa State University
Infestations of landscape pests may be slight or severe this year, so here's some advice for dealing with potential or existing landscape pest problems: check your plants weekly for evidence of pest activity to minimize plant damage. With spring nearly upon us, this advice applies to one of the earliest landscape pests, the small wasp called European pine sawfly (Neodiprion sertifer).
Déjà vu
If you have mugho, Scots, red or jack pines on your property, you may
remember finding one or more branches in late spring 2002 on which the
older needles were missing and only new, green growth was pushing out
of the terminal buds. The branches had a "lion's tail" appearance
and the plant looked sickly until the new needles elongated. You looked
around for evidence of an insect pest, but few definitive signs were found.
The culprit was the European pine sawfly.
Telltale signs
European pine sawfly survives the winter as eggs and larvae hatch in late
April to early May. The first sign alerting the gardener to larval hatch
is that the slits in the pine needle where the eggs were laid turn bright
orange. Newly hatched larvae feed on the outside green tissue of a pine
needle, leaving the structural, inner portion intact. This weakened tissue
turns yellow orange and curls or twists, much like the string ribbon on
a gift package does when curled with a pair of scissors. This "straw
stage" is another indication of European pine sawfly feeding.
Clusters of larvae
A closer examination of the pine branch reveals small, grayish green larvae
feeding in clusters. Each larva has a black head, black legs and a dark
stripe bordered by white stripes down the side of the body. When disturbed,
these larvae raise their heads and tail ends forming a "U" shape.
Immature sawflies feed in groups on the previous year's needles and eat
all needles on a single branch before moving to another branch to resume
feeding. They move to a new host tree once all previous-season needles
have been eaten.
As the larvae grow, they consume the entire needle down to where it attaches to the twig, leaving the paper sheath intact at the base of the needle cluster. Full-grown European pine sawfly larvae are about 1 inch in length. When mature, sawfly larvae either drop to the ground or find protected sites on the host plant and spin their cocoons. They live inside these hard, brown shells during the summer in two resting phases (prepupa and pupa).
Adult sawflies
Adult sawflies emerge during September and October. Females release a
sex attractant (pheromone) that draws in males. After mating, females
deposit eggs in new pine needles by using a saw-like tube, thus the common
name of this insect. The eggs remain inside the needles until the following
spring. There is only one generation each year for this species.
Damage
Defoliation by European sawflies lasts 4 to 6 weeks, usually peaking at
the end of May. Removal of last year's needles can be extensive, resulting
in isolated bare branches with a tuft of current season needles at the
end (lion's tail). Damage is variable from tree to tree and year to year.
This pest seldom kills trees because only older foliage is eaten, but
repeated defoliation over several years can slow tree growth. European
pine sawfly larvae avoid eating new needles but may feed on the bark of
new shoots, resulting in isolated twig mortality.
Sawfly management
Pruning off and discarding the clustered larvae shortly after they start
feeding can control European pine sawfly on landscape trees. Another simple
management tool is to shake the sawfly-laden branches over a bucket of
soapy water and then dispose of the collected larvae.
For plantings with multiple trees (e.g., windbreaks, golf courses, large corporate grounds or Christmas tree plantations) or with very heavy sawfly populations, insecticide sprays are available. Foliar applications of horticultural oil, insecticidal soap or Sevin control this pest. Wherever possible, spot treat clusters of sawflies, not the entire tree. Sprays are most effective when larvae are about 0.5 inch in length. Please read and follow all label directions.
Occasionally, a naturally occurring viral disease kills European pine sawfly larvae. The affected larvae hang head down from a pine branch. Collect these sawflies, place them in nonchlorinated drinking water, and then put the mixture in a small spray bottle in the refrigerator. The bottle can be retrieved the following spring, shaken well, and then used to spray new European pine sawflies feeding on your pine tree. The viral disease kills the larvae within a few days. Maintaining this management practice requires that diseased larvae be collected each spring.
-30-
|
Editors: Three color photos, suitable for publication, are available at right. Click on each thumbnail photo to go to the fullsized photo. The first picture's fullsize photo is 396K; the second picture's fullsize photo is 588K; and the third picture's fullsize photo is 436K. Caption 1: European pine sawfly larvae feeding on mugho pine |
 |
| Caption 2: Damage to a mugho pine by European pine sawflies |  |
| Caption 3: Orange oviposition sites indicate upcoming larval hatch |  |
Extension programs are available to all without regard to race, color, national origin, religion, sex, age, or disability.