| Abstract |
- The balsam woolly aphid (Adelges piceae (Ratz)), an
European pest of conifers, was first discovered in the
Pacific Northwest shortly after 1930. Control measures
of a chemical, silvicultural, or biological nature have
been proposed. However, present control methods are either
too costly or do not result in satisfactory control of the
aphid.
Several insect species were reported as predaceous
upon the balsam woolly aphid in Europe, eastern Canada,
and the Pacific Northwest. European predators of this
pest have been imported into eastern Canada in an effort
to find a satisfactory control measure. Several species
of insects from Europe were imported into the Pacific
Northwest from 1957 through 1959. Laricobius erichsonii
was successful in becoming at least temporarily established
in this region and was chosen for further study.
The purpose of the thesis project was to obtain information
on the establishment, life history, habits, and
effectiveness of this beetle in Oregon and Washington.
Studies were begun in May of 1958 and terminated in
November of 1959.
Two species of the genus Laricobius are indigenous
to the Pacific Northwest. Franz has studied the life
history and ecology of L. erichsonii in Europe, and Clark
and Brown have made observations of establishment, spread,
life history, habits, and effectiveness in eastern Canada.
In 1958 and 1959, 10,125 L. erichsonii, adults were
collected in Czechoslovakia and sent to the Pacific
Northwest Forest and Range Experiment Station in Portland,
Oregon, for release in the Pacific Northwest. Predators
were released either freely or in cages at eight different
areas in Oregon and Washington. Temporary establishment
occurred at all of the release areas regardless of
varied weather and elevational differences.
Some 52 larvae were collected and mounted on slides
in 1959. Of these larvae, no first, one second, four
third, and 47 fourth instars were present. First and
second instar larvae tend to stay within the aphid's wax
masses, while third and fourth instar larvae wander about
the bark in search of food. Moulting was observed. At
the various release areas, larvae were recovered from
May 23 through August 26 of 1959 and adults from May 5
through September 2.
Two pupae were laboratory-reared from five, field-collected
fourth instar larvae. Under laboratory conditions,
one fourth instar larva consumed or destroyed seven
eggs and two adults in a period of one and one-half hours.
L. erichsonii adults prefer aphid adults but attack other
stages.
Range of observed dispersal, a year following release,
ranged from zero to 75 feet from the point of original
release.
A study was initiated at Benton-Lane, Oregon, to
study the effectiveness of L. erichsonii in reducing
balsam woolly aphid populations. Trend of host populations
was evaluated at approximately two week intervals
on six unprotected and two protected (control) one-inch-square
bark plots on a pole-sized grand fir surrounded by
a six-foot-cube study cage. On the protected plots, the
average aphid population increased from 31 to 131 individuals
in the period from May 1 through November 23 of 1959,
while on the unprotected plots it increased from 47 to 64
individuals.
A t-test was calculated to see if the differences
between protected and unprotected plot populations were
significant. The t-value obtained was 4.3, which showed
that the differences were significant at the one per cent
significance level.
It is felt that populations of the balsam woolly
aphid will be greatly reduced when L. erichsonii can combine
with other predators that are fairly host specific
and that prey on all stages of the aphid.
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