;TATE P&AN B:oARD
ET-178 August 1941
United States Department of Agriculture
Bureau of Entomology and Plant Quarrantine
A DEVICE FOR ESTIMATING THRIPS POPULATION ON CITRUS FOLJAGE
By E. A. McGregor, Division of Fruit Insect Investigations
It is very difficult to make population -ons of the citrus
thrips (Scirtothrips cirri (Moult.)) bicnue i .sects are
small, active, and easily disturbed, and their oo lends with
that of the foliage of the host. Because o. th iculty the
writer developed a number of years ago a "> p v, herein
described, for obtaining indices to thrips populati.
The thrips meter consists of four items of eq Ln (fig. 1),
each of which will be described separatel is a light,
durable box, 8 by 6 by 2-1/2 inches in d!%e>si A cigar box
will fill these requirements. At one end of of he box
is placed a spring catch and at the other eni a le to hold in
place items 2 and 3.
Item 2 is a sheet of black paper to vw ioh- applied a thin
film of sticky material, such as tanglec i a h fits into
the bottom of the box, For convenience i handLi tie margin of
this sheet is left free of the sticky su>sane-; ;i reduces its
effective adhesive area to about 23 square inche- -. paper is
used, as the pale insects are readily soen an. counted on a dark
background. This item is referred to as h cpti>e icet.
For the Dreoaration of the capture sheets tH oky material
is applied with a painter's brush. A supply o- e sets may be
prepared in advance and stuck face to face to 0 i use. Care
should be taken to apply the sticky fluid as a cent ous film of
proper thickness. IT is important that 'e Do -ickv acea
of the sheet be aiwaYs Tne same, otherwise te roor, obtained
would not be comqarable.
Item 3 is a frame or wood or tnicX cara oara or trie same
over-all dimensions as the sticky sneet. A one eln. it fits ua-
der the ledge in the box and at the other end under nm spring catch.
The frame is put into place, or removed, by me-ans oa ::oo ia tened
to mhe upper surface or the frame on the end tha ts under Lne
ledge, and is held in place by the ledge and the spring catch. The
opening of this frame corresponds in size to the effective sticky
area of the sheet and exactly registers with it.
- 2 -
Item 4 is a cover of wire screen soldered to a frame of
light angle material made of tinned sheet iron. fitting snugly over
the box. The mesh of the screen is large eough to permit the
thrips to fall through and at the same time prevent larger insects
and trash from passing through to the sticky sheet.
When the device is assembled for use, the arrangement is as
follow: The adhesive capture sheet lies directly on the inner
bottom surface of the box. the frame lies immediately over the cap-
ture sheet, and the screen cover fits snugly over the box opening.
Both larvae and adults of the citrus thrips feed by pref-
erence on the tender twigs or terminals of the citrus trees, and
these new growth terminals are used as the units of measurement for
the thrips counts. The twigs are beaten upon the screen with the
thrips meter held in a horizontal position (fig. 2), and the in-
sects fall through the screen and are retained by the sticky capture
To facilitate the counting of the insects, the sticky sheet
is removed and cut into smaller pieces, usually six. Counting is
further aided by cutting a series of intersecting cross lines into
the surface of each small piece of the capture sheet. It is prefer-
able to make the count in the field with a hand lens before the in-
sects have had time to become quiet or settle into the sticky
fluid, when counting becomes more difficult. If necessary, however,
the counting may be done later in the laboratory, with either a hand
lens or a binocular microscope.
Figure 1.-Four component parts of the thrips meter:
1, Light box; 2, capture sheet provided with a film
of sticky material; 3, frame serving to hold the
paper in place and standardize the area of capture;
4, screen cover.
Figure 2.-Thrips meter in use in an orchard.
UNIVERSITY OF FLORIDA
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