Control of houseflies by fumigant activity

This invention relates to a novel method and composition for controlling houseflies by fumigant activity by contact with the vapors of the compound O-(4-methylthiophenyl)-O,O-dimethylphosphorothioate.

This invention relates to a method and composition for controlling 
houseflies by fumigant activity, that is, contact with the vapors of an 
insecticide compound. 
Insecticides have been found which function to control insects when applied 
in a number of different ways. For instance, an insecticide may be sprayed 
onto the walls of a building or other structure to control insects by 
contact with residual amounts of insecticide remaining after volatile 
components of the sprayed mixture have evaporated. Such control is 
generally termed "residual spray action". Other methods of controlling 
insects involve, for instance, direct sprays onto insects or into areas in 
which insects are to be found. Such sprays may be in concentrated or 
dilute form and applied by various ground or air spraying techniques. 
A relatively small number of insecticides have been found to control 
insects by what is known as fumigant activity, or fumigation. Such 
activity involves controlling the insects by contacting them with the 
insecticide in a vapor form. In one manner, used for eradicating insects 
inside a structure, the structure is sealed, and quantities of vapor of 
the insecticide are introduced into it. The vapors of the insecticide may 
be produced by a number of ways, for instance, by heating the insecticide, 
sometimes together with combustible material or volatile materials, for 
instance, by hot-plate or electrical coil, to vaporize the insecticide 
(optionally together with other ingredients in the mixture). 
Another method of fumigation involves indirect contact of the insect with 
the insecticide and consists basically of placing an absorbent material, 
such as a solid fibrous support formed from a felt of wool, a cellulosic 
fiber material such as cotton, paper or cardboard, or a synthetic fiber, 
or a cardboard of glass fibers, on which the insecticide has been absorbed 
or supported in solid or liquid form, in an area in which insect control 
is desired, and permitting the insecticide to vaporize naturally, so as to 
produce vapors of the insecticide in the area to be controlled, which 
contact the undesirable insects. This is considered indirect contact as 
the insect does not physically contact the insecticide in its liquid or 
solid form. 
It has now been found that the compound 
O-(4-methylthiophenyl)-O,O-dimethylphosphorothioate, 
##STR1## 
possesses the capability of controlling insects, particularly houseflies, 
by such fumigant, or indirect vapor, contact. 
The subject compound is disclosed in U.S. Pat. No. 3,042,703 (Example 8) as 
one of a series of thiophosphoric acid esters having insecticidal 
properties. Among the other compounds disclosed in this patent is the 
commercial insecticide fenthion, O,O-dimethyl O-(4-methylthio-m-tolyl) 
phosphorothioate, 
##STR2## 
which is described in Example 1. This compound has been used to control 
insects in a number of ways, including residual spraying in barns and 
stables, and by low concentration aerial spraying to control mosquito 
larvae. 
U.S. Pat. No. 3,042,703 states that the compounds described therein, which 
include both fenthion and the compound which is the subject of the present 
patent application, are insecticides that control, for instance, aphids, 
flies, mites, and lice. In general, it is stated that the compounds may be 
applied in rather low concentrations, including by means of aerosols. 
Various examples are given of the control of various insects by specific 
compounds encompassed by the patent disclosure. In all cases, it appears 
that the compounds were used in a direct contact, low concentration 
method, with concentrations generally being from about 0.0001 to about 0.1 
percent. No indication is given in this patent that the compounds would 
have any effect in vapor form, and the only conclusion which could be 
drawn from reading it is that the compounds are contact insecticides.

EXPERIMENTAL PROCEDURE AND RESULTS 
To demonstrate the unexpected vapor or fumigant activity of the subject 
compound, comparative tests were conducted, on houseflies, with this 
compound and three commercial insecticides of similar structure. The three 
commercial insecticides were: fenthion, 
##STR3## 
which is described earlier in this text; fenitrothion, O,O-dimethyl 
O-(4-nitro-m-tolyl) phosphorothioate, 
##STR4## 
and sulprophos, O-ethyl O[4-(methylthio)phenyl] S-propyl 
phosphorodithioate, 
##STR5## 
The tests were conducted in the following manner: 
CONTACT RESIDUE PROCEDURE 
Test compounds were diluted in acetone and aliquots pipetted onto the 
bottom of aluminum dishes. To ensure even spreading of the chemical on the 
bottom of the dishes one ml of acetone containing 0.02% peanut oil was 
also added to each dish. After all solvents had evaporated the dishes were 
placed in circular cardboard cages containing 25 female houseflies, one to 
two days old. The cages were covered on the bottom with cellophane and on 
the top with netting, and each contained a sugar-water saturated cotton 
plug for maintenance of the flies. Mortality was recorded after 48 hours. 
Test levels ranged from 100 .mu.g/25 female houseflies down to that at 
which approximately 50% mortality occurred. The LD.sub.50 values are 
expressed in the following Table I in terms of ug of the test compounds 
per 25 female houseflies. 
FUMIGATION ACTIVITY PROCEDURE 
Test compounds were diluted in acetone and aliquots pipetted onto 55 mm 
filter paper disks in the bottom of aluminum dishes. Immediately after the 
acetone had completely evaporated the dishes were placed in circular 
cardboard cages containing 25 female houseflies. The cages were sealed on 
both ends with cellophane and each contained a sugar-water saturated 
cotton plug for maintenance of the flies. A piece of netting was placed 
over the aluminum dish in the cage in such a way that the flies were 
unable to come into direct contact with the chemically treated filter 
paper. Mortality was recorded after 48 hours. Test levels ranged from 100 
.mu.g/25 female houseflies down to that at which approximately 50% 
mortality occurred. The LD.sub.50 values are expressed in the following 
Table I in terms of .mu.g of the test compound per 25 female houseflies. 
TABLE I 
______________________________________ 
Contact LD.sub.50 
Fumigant LD.sub.50 
Compound .mu./25.degree. flies 
.mu.g/25.degree. flies/285 cc. 
______________________________________ 
O--(4-methylthio- 
0.85 2.1 
phenyl)-O,O--dimethyl 
phosphorothioate 
Fenthion 2.9 14.3 
Fenitrothion 4.0 &gt;100 
Sulprophos 12.0 &gt;100 
______________________________________ 
Thus, the subject compound O-(4-methylthiophenyl)-O,O-dimethyl 
phosphorothioate, while showing approximately four times the activity of 
fenitrothion in the contact tests, was at least 50 times as active as this 
compound as a fumigant. Fenitrothion is known to possess some, but only 
moderate, fumigant activity. See, for instance, U.S. Pat. No. 4,228,124. 
The 4-methylthiophenyl compound which is the subject of this invention 
surprisingly possesses an immensely improved fumigant activity with 
respect to fenitrothion, sulprophos, and even fenthion, which activity 
would not be expected from any of the information known in the art. 
For use as a fumigant, the 4-methylthiophenyl compound may be incorporated 
in or supported on a solid porous or fibrous support. Such support may be 
formed, for example, by a paper, a felt of wool, cotton and/or synthetic 
fiber, compressed cellulose such as wood fiber, cereals, alfalfa or 
cotton, a felt card, a card formed from old papers, or from glass fiber. 
Alternatively, the compound may be incorporated into a plastic or polymeric 
composition formed for instance, from a polymeric resin, plasticizer, and 
other typical ingredients, into which the subject compound may be 
introduced and the resulting composition rolled or cast out as a sheet or 
other solid form, or utilized as a coating medium for coating on, for 
instance, paper, or other material. In any or all of the above forms, the 
subject compound may be incorporated in a microencapsulated form or other 
form with adjuvants which result in slow or controlled release of the 
subject compound vapors into the surrounding atmosphere. 
In general, in such forms, the subject compound will be present in a 
concentration of from about 1 to about 50 weight percent.