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In a recent issue of Scaffolds (1999, vol. 4),
Dr. Art Agnello from Cornell University described the insect as follows:
"The pear thrips (Taeniothrips inconsequens
[Uzel]) is an unusual insect about
1/20 inch long, with fringed wings and asymmetrical mouthparts. The adult pear
thrips is slender and brown, with short antennae and a swelling behind the head; the wings
are long and narrow, with fringes of long hairs. Young pear thrips are small and
white with red eyes. ("Thrips" is the term used both for one or for
many.) Mouthparts consist of a pair of stylets for puncturing plant tissue, plus a
cone with a rasp-like surface, which is used for roughening the wound and then sucking up
the juices.
Pear thrips, originally from Europe, were introduced into California at the turn of the
century, where they demonstrated a taste for plums, cherry, apple, and pear; other hosts
are basswood, birch, beech, ash, and of course, maples. It is the adult thrips that
appear on host trees in great numbers and do the most destructive damage. Generally
speaking, they arrive just before or during the opening of fruit buds (late April for New
York apples and pears). They enter the bud, or start feeding on the bud tip and
gradually work themselves in. Eggs are laid under the bud scales, petals and sepals,
on stems and in other succulent flower and leaf parts. The larvae feed voraciously
for about 3 weeks, adding to the damage already caused by the adults. After the
larval feeding period has finished (early June in N.Y.), they drop off the tree and enter
the ground, often to depths a foot or more, where they enter a diapause stage until
fall. Sometime in September or October, they pupate in their earthen cell, and
remain until the adults emerge the next April. Under natural conditions, the
duration of a single adult's life probably covers a period of 4-6 weeks.
On fruit trees, feeding is usually concentrated on the tender flower parts, which gives
the blossom buds a shriveled, scorched appearance, or causes them to fall off
completely. Foliar damage in hosts such as maples is caused by the insects' feeding
on the developing leaf tissue; this results in leaves that are dwarfed, mottled yellow to
green-brown, and distorted. Small scars resembling blisters show up along the leaf
veins and stems. The tree will consequently have a thin crown, possibly suffer some
moisture stress, and may even drop its leaves prematurely in the fall.
Because much of this insect's life is spent underground, control of damaging populations
is very difficult. Insecticides have been suggested by some, but their effectiveness
is difficult to measure, because most growers are not aware of the damage until after it
has already been done, although thrips are sensitive to nearly any prebloom
insecticides used in most commercial orchards On fruit trees, an oil spray is
advised against the egg-laying adults as they emerge, timed between the bud burst and
green cluster stages of pear and plum (usually the 2nd or 3rd week of April). This
can be a prudent treatment to apply in any case, as a preventive measure against other
pests such as mites or pear psylla. Massachusetts guidelines suggest that it can be
useful to examine fruit buds at this time to determine whether thrips are present."
It is good to be aware of this insect since it has caused damage in some Vermont orchards
in the past.
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