STATE I I3ARD E-683
United States Department of Agriculture
Agricultural Research Administration
Bureau of Entomology and Plant Quarantine
USX 07 DDT TO CONTROL THE LITTLE FIRE ANT
By Max B. Oeburn and N. Stabler,
Division of Fruit Insect Investigations
The little fire ant (Wasmannia aurolunotata (Roger)) is a seri-
ous pest to citrus-grove workers in some sections along the east
coast of Florida. The ants nest in the soil or under debris, such as
fallen branches and fallen leaves, and. visit the citrus trees to ob-
tain honeydew secreted by whiteflies, mealybugs, aphids, and other
insects found on citrus. In some groves great numbers of these ants
are present, and'it is impossible for workers to pick fruit, prune,
or spray Vithout becoming covered with them and being stung many
times. A single sting causes considerable irritation to most individ-
uals. The characteristic symptoms are a welt surrounded by a red,
splotchy area, and a severe burning and itching sensation which may
prevail for 30 minutes or more. Even after most of these symptoms
disappear, the itching may recur at intervals for several days.
Workers in citrus groves, especially fruit-picking crews, have refused
at times to work in trees infested with this ant. In other instances
pickers have left the trees partially picked, or have demanded a
Results of experimental work conducted during the last few
years on the control of this pest, in which poisoned baits and other
insecticidal treatments were tested., have not been satisfactory.
Sprays containing oil, pyrethrum, derris, or dinitro-o-cyclohexyl-
phenyl will destroy many ants, but heavy ireinfestation occurs in a
week or two following treatment. DDT has been found to be much more
toxic, and to provide more permanent control than any other material
tested. Although many factors affecting the use of DDT for control of
this ant remain to be studied, early results of tests with it have
been so outstanding as to Justify the issuance of preliminary informa-
tion concerning its use for this purpose.
While complete information as to the length of the protective
period of different DDT formulations is not available at this time, a
given quantity of technical DDT in fuel oil applied as an emulsion
appears to be more effective than when applie& in any other way. The
preferred formulation consists of the following:
- 2 -
Technical DDT ................. j to 1 pound
No. 2 fuel oil ................ 1 gallon
Glyceryl oleate ................ 1.3 fluid ounces (38 ml.)
Water to make ****................. 100 gallons
This formulation is prepared for use by dissolving the DDT in the fuel
oil and then emulsifying the solution with the glyceryl oleate. Un-
doubtedly other emulsifiers of a similar nature would be equally sat-
isfactory. Applied to the entire inside of the tree, sprays contain-
ing 1/2 and 1 pound of DDT per 100 gallons have controlled this ant
and prevented reinfestation for a period of a year, while 1/4 pound
per 100 gallons of spray has done so for 9 months.
Other DDT formulations applied as sprays and dusts have given
control and prevented reinfestation for at least 2 months. Such for-
(1) 1/4 pound of technical DDT dissolve in 1 1/2 gallons of
emulsive spray oil and diluted with water to make 100
gallons of spray.
(2) 40 ounces of a mixture containing 10 percent of technical
DDT in pyrophyllite (1/4 pound of DDT) mixed with water to
make a paste and then added to water to make 100 gallons
(3) 20 or 10 ounces of a water-dispersible powder containing
40 percent of technical DDT (1/2 and 1/4 pound of DDT)
iA .xed with water to make a paste and then added to water to
make 100 gallons of spray.
(4) Same as (3) with addition of 1 1/2 gallons of an emulsive
(5) A 3-percent commercial DDT dust containing 1 percent of
(6) A 10-percent commercial DDT dust.
Two methods of applying the spray have proved satisfactory.
One method involves spraying the entire inside of each tree, paying
particular attention to covering the trunk, and the other involves
thoroughly spraying ohly the trunk and heavy lower limbs. The first
method requires about 12 gallons of dilute spray to do a thorough job
on a 20-year-old grapefruit tree, whereas the second method requires
only about 2 gallons. An effective formulation may prevent reinfes-
tation for as long as 12 months when applied by the first method, and
for only 1 or 2 months when applied by the second method, Advantages
of the second method are the saving in material and less danger of ad-
verse effects on beneficial insects, because very little'of the spray
is deposited on the upper portion of the tree.
Dusts should be applied with a power outfit to two opposite
sides of the trees, at the rate of about 1 pound of dust to a 20-year-
old grapefruit tree. As with the sprays, particular attention should
be given to covering the trunk and larger lower limbs.
No injury to grapefruit trees that have been sprayed or dusted
with the formulations listed has been observed.
UNIVERSITY OF FLORIDA
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