# Patent

## Title
Synergistic pesticidal compositions

## Abstract

This is a division of application Ser. No. 07/666,563, filed Mar. 8, 1991, now U.S. Pat. No. 5,135,750, which in turn is a continuation of application Ser. No. 07/326,674, now abandoned.

## Background
This invention relates to an innovative pest control agent and its usage.

Insect pests cause considerable economic damage to people. However, insect pests are also species of insects. Insects play important roles in the economy of nature. We must consider methods for controlling insect pests to decrease the economic damage they cause without destroying the natural world.

Insect pests such as termites cause economic damage to artificial structures. The amount of the damage is equivalent to that caused by a fire. Termite damage was once limited to wooden structures. However, as man's culture develops and man's living conditions change, the damage extends to new building materials, reinforced concrete structures, transmission cables and telecommunication cables. As a countermeasure, we rely on chemical agents. Various termite-proofing agents are available on the market.

Household insect pests such as termites, ticks, fleas and moths rapidly proliferate, causing economic damage and mental stress to people. When structures are infested with these insects, insect-control and preventive measures must be immediately taken.

The measures depend on the chemical pest control agents available on the market. The agents contain inorganic compounds (e.g. arsenic, boron, molybdenum) and organic compound (e.g. phosphorus, synthetic pyrethrin, IPWC). Certain chemical pest control agents are poisonous to people, and harmful to the environment. The workers at insect pest control companies and the inhabitants in the structure where the control agents have been applied worry about their health.

In the present invention, specific nontoxic silica gels are used as substitutes for the poisonous and polluting chemical agents used to prevent household insect pests from rapidly developing large populations. By applying the silica gels to the structures constructed with new building materials, the humidity in the structures is controlled to maintain a comfortable environment for people.

The present invention provides silica gels for sticking to, absorbing moisture from, and killing insect pests, comprising at least 0.05% by weight of silica-gel particles with a diameter of 50 .mu.m maximum.

The invention may be best understood by referring to the following description of the preferred embodiment and the drawings in which:

FIG. 1 is a distribution graph of silica-gel particle diameter, in which a bar chart shows the percentage by volume of particles of silica gel by particle diameter and a polygon shows the relationship between the percentage by volume of the particles in the silica gel and the particle diameter;

FIG. 2 is a graph showing the relationship between the mortality of reticulitermes and time at various relative humidity levels;

FIG. 3 is a graph showing the relationship between the mortality of coptotermes and time at various relative humidity levels;

FIG. 4 is a graph showing the relationship between the mortality of reticulitermes and time after the exposure of the reticulitermes to Home gels;

FIG. 5 is a graph showing the relationship between the mortality of coptotermes and time after the exposure of the coptotermes to Home gels containing 0.05% of fine particles for thirty to ninety minutes;

FIG. 6 is a graph showing the relationship between the mortality of coptotermes and time after the exposure of the coptotermes to Home gels containing 0.01% to 0.03% of fine particles for sixty to ninety minutes;

FIG. 7 is a graph showing the relationship between the mortality of Tyrophagus putrescentiae and time after exposure to the silica gels at the relative humidity of 70%.

FIGS. 8-12 are microphotographs of coptotermes' body portions (enlarged one thousand to three thousand times); and

FIGS. 13 and 14 are photographs of coptotermes after the exposure to the silica gels.

It is usually so humid, for example, under the floor of wooden structures that dew condenses and insect pests such as termites invade and proliferate. To control these insect pests, polyethylene film is first laid on the ground. Subsequently, silica gels containing at least 0.05% by weight of particles with a diameter of 50 .mu.m or less are sprayed evenly over the film at a rate of 3 kg/m.sup.2. The humidity under the floor is kept between 65% and 75% on average by the silica gels throughout the year. Insect pests can thus be controlled because the insect pests such as reticulitermes prefer more humid zones. By exposing invading insect pests to the sprayed silica gels, fine particles with a diameter of 50 .mu.m or less of the silica gels stick to the surface of the pests' body. The pests' tissues to which the silica-gel particles stick gradually decay, die and rot. As shown in FIG. 1, the diameter of the silica-gel particles should be 50 .mu.m maximum, preferably 10 .mu.m maximum, and 5 .mu.m maximum is best. The stricken insect pests or other pests cut the rotten tissues away. As time passes, the number of dead pests increases. The lethal effect of the silica-gel particles is limited to individual pests. The pests do not carry the lethal effects of the silica-gel particles to other pests. When the insect pests walk on or become exposed to the surface of the silica gels for sixty to ninety minutes, they die. By spraying the biotically-nontoxic silica gels in the structures, the invading insect pests can be controlled.

To obtain maximum lethal effect, the percentage of the particles with a diameter of 50 .mu.m maximum contained in the silica gels should be 0.05% minimum, preferably 1% minimum, and 2% minimum is best. However, when the silica gels contain too many fine particles with a diameter of 50 .mu.m maximum, the particles disperse in the air, inhibiting the silica gels from being sprayed evenly over the floor. Thus, the percentage of the particles on the silica gels should be 5% maximum. Specifically, the diameter of the silica gels (Home gel) is 350 .mu.m minimum. The silica gels control insect pests by controlling humidity in the structure. Each of the silica gels are covered with the particles. The particles are prepared by filtering the silica gels with a 50 .mu.m filter. The silica gels should contain 5% maximum by weight of the particles. The insect pests die by being exposed to the particles.

The lethal effect of the present embodiment is now explained referring to the graphs.

As shown in FIG. 2, when the relative humidity in the structure is adjusted to between 50% and 100% using humidity-controlling silica gels, reticulitermes can live only for forty hours at a maximum relative humidity of 80%. As shown in FIG. 3, coptotermes are brought to death or dehydrated at a maximum relative humidity of 60% within eighty hours. In both cases, termites cannot live long, because the silica gels adjusts the relative humidity.

An adsorbent drying agent adsorbs moisture faster than wood. The adsorbent drying agent can create the environment improper for the invasion or the infestation of insect pests. By adjusting the relative humidity with the adsorbent drying agent, termites can be brought to death quickly.

In this embodiment, the minute silica-gel particles with a diameter of 50 .mu.m maximum stick to the surface of the termites' body. The particles with the diameter greater than 50 .mu.m do not adhere to the surface of the termites' body. In FIG. 9, the particles which seem large are coagulated silica-gel particles. The silica-gel particles partially dehydrate the termites where the silica-gel particles stick to their tissues. The termites die with their tissues decayed by the silica-gel particles.

As shown in FIGS. 4-6, when the termites are exposed to the silica-gel particles for a long time, the mortality of termites increases. In FIG. 5, the silica gels are filtered with a 50 .mu.m filter to obtain the silica-gel particles with a diameter of 50 .mu.m maximum, and the silica-gel particle diameter distribution is shown in FIG. 1. Comparing FIG. 5 and FIG. 6 which differ in the silica-gel particle diameter, when the percentage of the fine particles with the diameter of 50 .mu.m maximum contained in the silica gels increases, the mortality of termites increases, accordingly. After the exposure of coptotermes to the silica gels, the hind leg of the one shown in FIG. 8 is covered with the silica-gel particles as shown in FIG. 9, its body surface changes as shown in FIG. 10, and its antenna shown in FIG. 11 changes as shown in FIG. 12. After coptotermes are exposed to the silica-gel particles, they first partially turn black as shown in FIG. 13. Subsequently, they almost completely turn black as shown in FIG. 14, and finally die.

The silica gels of this embodiment exert the lethal effect on the insect pests other than termites, such as Tyrophagus putrescentiae as shown in FIG. 7.

In this embodiment, humidity-controlling silica gels, an adsorbent drying agent, and Home gel refer to the same silica gels. Various types of the adsorbent drying agent are available. Even the adsorbent drying agent that is provided with the properties other than specified in this embodiment can control termites.

This is just one embodiment of the present invention. The claim is not limited by any of the details of this description, and should be construed broadly within its general principles.

## Claims

1. A method for killing insects by exposing insects to an insect-killing effective amount of a biotically toxic composition, consisting essentially of a relative humidity controlling effective amount of silica gel having a minimum particle size of 350 .mu.m, and about 0.05% to about 5% by weight silica particles having a maximum diameter of about 50 .mu.m.

2. A method for killing insects according to claim 1, in which the insects are coptotermes.

3. A method for killing insects according to claim 1, in which the insects are reticulitermes.

4. A method for killing insects according to claim 1 in which the insects are Tyrophagus putrescentiae.