Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SLOW RELEASE INSECT CONTROL PRODUCT
This invention relates to the formulation of a slow
release solid insecticidal product based on a polyvinyl chloride
(PVC) matrix for use on animals to control a variety of insects.
It is known in the prior art to make animal collars or
ear tags formulated to include insecticides for use to control the
population of face and horn flies on animals such as cattle. In
the case of ear tags, attempts have been made to use a combination
of insecticides, namely, cypermethrin (a type of pyrethroid) and
diazinon (a type of organophosphate) in combination with other non-
insecticidal ingredients in a PVC matrix to produce a tag which may
be clipped to a cow's ear. In the prior art, the mechanism of
action was thought to result from the insecticide being carried out
of the ear tag by the plasticizer ingredient of the formulation.
Prior art insect control products, which have been at all
effective, have all utilized liquid insecticides together with
other nontoxic ingredients for formulation of the product. The
prior art is also familiar with the principle of using a
combination of two insecticides each with a different mode of
action in order to delay the onset of resistance in the subject
insect.
Effective insect control is usually required for a 16
week period. In order to be effective for a full 16 weeks, the
chosen insecticide must be present in the insect control product
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in excess of the minimum effective insecticidal concentration for
the entire 16 week period. Where more than one insecticide is to
be used, each one must be present in the insect control product at
a concentration in excess of the minimal concentration toxic to the
subject insects, for the entire 16 week period.
The problems with prior art insect control products are
many.
The use of one insecticide alone has often resulted in
the development of resistance by the subject insect. Formulation
problems in prior art insect control products have often resulted
in lack of effective concentrations of the insecticide for the full
16 week period. The use of organophosphate insecticides by
themselves has failed due to the inability to get enough active
ingredient into the product and when the insecticide came out, it
either came out too fast or too slow. Prior art use of diazinon
has resulted in products which permit diazinon to come out of the
product at the right rate, although formulation limitations have
prevented getting a sufficiently high concentration of this
insecticide into the product to begin with. Prior art formulations
have resulted in compounds which have been difficult to handle
particularly when shaping animal ear tags. Prior art formulations
have resulted in products which are too moist and hence unworkable
into suitably shaped solid ear tags. Prior art attempts to obtain
drier formulations by adding more absorbent resin have resulted in
the disadvantage of hindering the ultimate release of the
insecticide. Prior art attempts to combine two insecticides having
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different modes of action have resulted in ineffective products as
a result of the individual insecticide concentrations being below
the minimum effective concentration.
In the prior art, the total concentration of active
ingredient in a PVC matrix was limited to 25% w/w. In practise,
when regular, low absorbent PVC is used, the concentration is
limited to 20% w/w. Above this concentration, too much of the
liquid part of the formulation remains unincorporated into the PVC
resin after compounding, and a free-flowing powdered compound is
not obtained. Given the activity, release rate and dissipation
rates of currently available insecticides, the concentration of the
active ingredients in the PVC matrix is the limiting factor in
achieving effective dose levels for a satisfactory interval of
time. This is further aggravated in the case of diazinon, by the
need for a stabilizer to prevent formation of toxic by-products in
the presence of traces of moisture. The prior art has attempted
to overcome this disadvantage, without success. Reducing the
amount of plasticizer, has resulted in a loss of flexibility and
weaker physical properties in the insect control product.
Alternatively, using a more porous PVC resin increases the cost and
results in weaker physical properties.
Accordingly, the prior art has been unable to overcome
the technical problem of incorporating insecticides into a slow
release formulation in the required concentration. The ingredients
of prior art formulations have been too moist to flow freely into
the molding machines used in making ear tags and other insect
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control products. Although, as previously already stated, it is
known to combine cypermethrin and diazinon, the highest
concentration possible using the prior art technology is 6%
cypermethrin and 11% diazinon which results in an inactive product,
the total concentration being below 20% w/w (minimum effective
concentration) in the product.
The present invention has overcome many of the
disadvantages present in prior art insect control products.
The present invention has made it possible to combine
two insecticides, each with a different mechanism of toxic action,
and each having a fully effective concentration providing for 16
weeks of fly control, into a slow-release insect control product
based on a PVC matrix, without using more costly forms of PVC. Key
to the present invention is the addition of a second active
ingredient which is in a crystalline state at normal room
temperature, such as alpha-cypermethrin, and when mixed with
another active ingredient and a suitable stabilizer and
plasticizer, results in a dry, free flowing compound capable of
ultimately being shaped into an ear tag or other insect control
product with good physical properties.
Accordingly, the present invention provides for a slow
release insect control product or device comprising at least two
active ingredients having different modes of toxic action, one of
which is a crystalline solid at room temperature, each in
sufficient concentration to provide at least 16 weeks of fly
control, in a regular grade polyvinyl chloride matrix with at least
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20% w/w of a suitable plasticizer and a suitable stabilizer. Two
preferred active ingredients are diazinon 18% w/w and
alphacypermethrin 4% w/w. Chlorpyrifos in a concentration of 18%
w/w may be used in place of diazinon. A preferred plasticizer is
dioctyl adipate. A preferred stabilizer is one containing
epoxidized soyabean oil. Such a slow-release insect control device
may be suitably shaped to avoid breakage and for application as an
ear tag.
Contrary to the prior art theory for the mechanism of
action of insect control products, the inventor herein, has
recognized that the plasticizer does not carry the active
ingredient out of the product but rather the active ingredient
moves to the outside of the tag via diffusion, where in the case
of an animal ear tag, the active ingredient is transferred onto the
hair of the animal by movement of natural animal hair oil,
continuously rubbed onto the tag and then back onto the hair. Once
on the hair, secondary movement is primarily by physical transfer
caused by the animal rubbing one area of hair against another. The
same direct contact mechanism moves the active ingredient between
animals. Consequently the activity of an animal ear tag is
determined on balance by the release of the insecticide from the
tag and the rate of dissipation of the insecticide from the hair
of the animal.
Generally, a slow release insect control product is a
mixture of dry ingredients (polymer resin, pigment opacifier, etc.)
and liquid ingredients which are blended in a mixture to make a dry
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free flowing coarse powder. Plasticizer ingredients provide
strength and suppleness to the formulation. Stabilizers allow
working of the plasticizer in the mixture without burning (free
radical inhibition). The resulting dry free flowing coarse powder
is then shaped via injection molding into the insect control
product, for example an animal ear tag.
The present invention recognizes the need to have during
formulation, dry ingredients in excess of 50~ w/w and liquid
plasticizer ingredients in excess of 20% w/w, otherwise the
resulting formulation is either a gooey mess or too stiff
(resulting in excess breakage). Those persons skilled in this art
will recognize the upper limits of the % w/w of these ingredients
suitable for formulating a product which will have the desired
characteristics.
The present invention recognizes that use of a
crystalline solid insecticide will provide a free flowing
formulation capable of being shaped into an effective insect
control product. The present invention utilizes alphacypermethrin
which is present at room temperature in crystalline form and which
is more active than plain cypermethrin. Other insecticides in
crystalline form at room temperature may also be used. The present
invention recognizes that when technical grade diazinon and
alphacypermethrin are used in a concentration within the range 16 -
20% w/w and 4 - 8% w/w respectively, with at least 20% w/w of a
plasticizer, namely, dioctyl adipate in a regular grade of
polyvinyl chloride resin, with suitable stabilizers, a dry free-
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flowing powdered compound is obtained.- Preferred concentrations
of diazinon and alphacypermethrin are 18% w/w and 4~ w/w
respectively. An alternate to the use of diazinon is chlorpyrifos
16 - 20% w/w (with 18% preferred). Other suitable plasticizers,
including but not limited to polymeric plasticizers, known to those
skilled in the art may also be used. Opacifiers and colourants are
optional. The aforesaid compound is easy to handle in production
equipment and provides molded products having acceptable physical
properties.
Those skilled in the art will recognize, when using
diazinon and alphacypermethrin within the aforesaid ranges, that
increasing the concentration of one of these insecticides should
be balanced by decreasing the other within the prescribed range.
Sample formulations are set out hereinafter:
Formula #l
Inaredients % w/w
Alphacypermethrin (96.7%) 4.15
Diazinon 95% 21.03
Dioctyl adipate 20.07
Stabilizer 1.48
Polyvinyl chloride resin 53.27
Pigment and opacifier .0008
Formula #2
Inaredients ka/1000 ka
Fastac Techn.*
(alphacypermethrin) 96.7% 43.02
Diazinon Stabilized 87.27% 214.51
Dioctyl adipate 208.00
Stabilizer #1 5.00
Stabilizer #2 7.50
Stabilizer #3 3.00
Opacifier 5.00
Irgalite* Blue BLP 0.30
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Irgalite* Yellow BAF 0.70
Geon* 103 EP F-76 (PVC) 512.97
1000 . 00
*Trade-marks
The aforesaid insecticide combinations including
alphacypermethrin and diazinon provide effective concentrations,
assist in making a solid tag and furthermore assist in permitting
the insecticide to diffuse out of the tag so as to provide a full
16 weeks of fly control.
The present invention achieves a delayed onset of
resistance by using two active ingredients with different toxic
actions each at fully effective doses. As a result, the individual
insects must possess tolerance to both insecticides simultaneously
in order to survive. This is much less probable than the presence
or development of tolerance to a single insecticide with a single
toxic action.
When a trial batch (see Formula #l) was made into ear
tags and tested on cattle, excellent control of Haemotobia Irritans
(horn flies) was obtained. Control was limited only by a technical
problem with tag breakage, which was overcome by changing the tag
shape. Therefore, the present invention has made possible the
control of horn flies, even those which have become tolerant to
pyrethroid insecticides, for a 16 week period.
