1. Field of the Invention
The present invention relates to the problem of eradication of troublesome colonies of insects, and more particularly, to extermination of the species of imported fireants termed "Solenopsis invicta" and "Solenopsis richteri."
2. Background of the Prior Art
Imported fireants (order Hymenoptera, Family Fomicidae, species "Solenopsis invicta" and "Solenopsis richteri") are extraordinarily aggressive, destructive insects capable of significant environmental damage, as well as inflicting human and animal suffering in the parts of the country which they inhabit. Imported here accidentally from South America sometime before World War II, these terroristic insects have now spread at an alarming rate across some 216,000,000 acres of land in 15 Southern States. They are steadily migrating northward and eastward each year.
These seemingly indestructible insects have been responsible for an estimated 300,000,000 human stings a year, sometimes severe enough to result in death, particularly in young children and the elderly. Fireants show no fear and will savagely attack and kill any ground dwelling insect and have been known to kill animals as large as cows. Farmers have suffered great economic loss as a result of damaged farm equipment, mutilated crops, and lost livestock.
Relying on a phenomenal reproductive capacity, thousands of "worker ants" are born to a "queen" over just a few days. The worker ants then proceed to build large ant mounds with interconnecting tunnels. The mounds may be found in yards, school playgrounds, open fields, and along roadways, often in concentrations as high as 400 mounds per acre. The mounds range in size from a few inches to several feet in diameter, and sometimes extend to below ground depths of up to six feet. Lateral tunnels often radiate outwardly to an average of perhaps 75 feet and a maximum of 130 feet. These tunnels have entrances and exits to and from the surface which the fireants use in their foraging excursions.
Efforts at control have had only limited success. In the past efforts have concentrated mainly on the use of environmentally hazardous chemical pesticides and baits which are not target specific and which have detrimental ecological effects. In addition, chemical control has been limited in achieving lasting success because of the rapid reproduction and replenishment of fireant colonies.
In the patent literature, typical examples of techniques that confront the problem include U.S. Pat. No. 4,756,118, issued Jul. 12, 1988, to Charles W. Evans, II. The Evans patent discloses a high pressure, high temperature vaporizing system and an insertable probe or lance mechanism together with other associated elements. By these means thermal vapors or gases comprising principally insecticides and diluents are injected into the core of a mound while maintaining a high pressure and temperature. The theory is that dispersion of the insecticide gases will carry through the entire mound and a substantial part of the tunnel system, destroy the queen and all fireants with which the gases come in contact. However, this approach not only relies primarily on the killing power of the insecticide, with its attendant expense and ecological after effects, but presents inherent dangers in terms of the ranges of temperature (2210.degree. F.) and pressure (as high as 3000 psi) that are used. The volume of liquid delivered is kept low, because reliance is placed on the spread of the killing gases.
Other patents evidencing the state of the art include U.S. Pat. No. 4,160,336, issued to Query et al. Jul. 10, 1979. This proposes a technique in which a refrigerant and an insecticide are injected as an aerosol into the individual mounds. As with the Evans II patent, the usage of an insertible probe for dispersion of vapors is not an assured method of delivery, since a mound comprises a plurality of interior tunnels and galleries. In addition, if the probe is not fortunately positioned, the flow may be occluded and have very limited or only partial penetration. The same is true of the U.S. Pat. to Turner, No. 4,367,161, issued Jan. 20, 1987. This is a probe system that utilizes pressurized steam injection, employing a probe that is injected vertically downward into the mound within a proprietary doomed shield with a vent opening. The patent suggests that condensation of a portion of the injected steam into very hot water will aid in the extermination of target insects or animals, but it is evident that only a very limited amount of water can be delivered in this manner. The U.S. Pat. to Connelly, No. 4,815,234, issued Mar. 28, 1989 proposes a combination of mechanical destruction of the ant bed, combined with delivery of a stream of high temperature fluid, which might include water, to kill the fireants. However, fireants are extremely sensitive to disturbing influences, and at the onset of danger the ants transport the queen or queens to different areas. Thus, in an area where there is a substantial concentration of ant mounds, such mechanical disruption has a possibility of being ultimately effective only with the first mounds so treated.
It is evident therefore that a need exists for methods and apparatus which can operate effectively to destroy fireant populations using ecologically safe materials of low cost, overcoming the problems that have been encountered by the prior art.