Perimeter Baits Or Sprays?

Ant control strategies may be changing. For decades, PCOs have applied an emulsion or granules to the turf around a structure to kill ant colonies and to create a barrier to prevent entry into the building. Labels call for treatment of a band from 6 to 10 feet from the building and about 3 feet up the base of the wall. When the label is followed, this treatment has been effective in most applications to prevent some ants, cockroaches and incidental crawlers from infesting buildings. But for some ants, this strategy has offered only limited success.

There are several good reasons for this:

1. Constrained by low bids, only 3 or 4 feet of the turf is usually treated;

2. Lower-cost formulations instead of microencapsulated products are used;

3. Recently treated grass is mowed, along with pesticide residue;

4. Sun, heat, rain and dew degrade the toxicant;

5. Organic elements in the soil withhold the toxicant;

6. Ants trail on plants growing above the barrier, especially trees and bushes that touch the wall; and

7. Ants enter structures via overhead utility lines.

This means that for most of the month, no effective control is in place. The practice of broadcasting pesticide on the turf around a structure may soon be curtailed because of various anti-pesticide legislation. Today, it is appropriate for PCOs to consider alternatives to conventional, scheduled blanket coverage of the turf surrounding a structure as a barrier against ants in general.

For some species of ants, the practice of broadcast spraying is counterproductive. In the 8th edition of the Handbook of Pest Control by Arnold Mallis, Hanif Gulmahamad notes that "pyrethroids cut off satellite colonies of Argentine ants inside buildings, causing them to more actively forage throughout the structure, creating numerous customer complaints and requests for additional services." The use of a pyrethroid in broadcast perimeter treatments for Argentine ants is not recommended by Gulmahamad.

Baiting for ants outdoors appears to be one of the best alternatives to the use of perimeter applications of pesticides. If the colonies outdoors are eliminated, it is not likely that more ants will enter from the outside. Colonies already established indoors could be eliminated by conventional means.

CASE STUDY. The white-footed ant, a multiqueen ant, rivals the Argentine ant in egg production and develops massive colonies. It feeds mainly on sweets from aphids, mealy bugs and scale insects and readily imbibes on sugar water as does the Argentine ant. Several PCO firms in southern Florida will not give more than a two-month guarantee. So I decided to try to control the white-footed ant that plagues many parts of Florida. I placed bait stations (with JT Eaton’s Dr. Moss Liquid Ant Bait) outside at infested sites. I figured that if I could control white-footed ants, I could control any species.

Similar infested buildings had the perimeter sprayed with Dursban with no bait stations. There was a marked reduction in callbacks with the condos protected with the bait stations. However, it did not take long for new colonies to move in to replace the dead ones. After two months, they began to return and feed on bait even if it had a slight crust of fungi. With multiqueen species that can develop mega-colonies, there is no solution other than year-round maintenance of the stations. In addition to white-footed ants, other species controlled were ghost ants, crazy ants, Pharaoh ants, Camponotus floridanus, Wasmania and pseudomyrmex.

GOING TO THE SOURCE. In IPM Practitioner, January 2000, I found support for the idea of controlling indoor ant infestations by controlling the colonies outside. It is a story about Arthur Slater, a pest management innovator who is responsible for pest control at the University of California, Berkeley, for 632 buildings and 14 million square feet of structures and also vector control on 1,500 acres. He has applied his background in research to test various strategies to control pests with the least impact on the environment, often collaborating with Drs. Mike Rust and Don Reierson. For many years he has been getting excellent control of ants with outside baiting.

He writes, "we never bait inside because baits attracts the ants and we don’t want ants inside." He goes on to write, "liquids or semi-liquids are much better for (the ants) than solids because solids have to be fed to their larvae, which then liquefy it and feed it back to the adults. The best time to bait ants is when they aren’t a problem, six months out of phase, because the ant populations are low. When the ants have brood they enter homes in search of food." This supports the idea of maintaining bait stations year round where ants are active outdoors. He warns that baiting takes much longer than sprays to destroy a colony, but the apparent absence of ants after a spray job does not mean that a fragmented part of the colony isn’t developing a colony nearby. One of Slater’s tricks to attract ants to his bait stations is to soak strings in the liquid bait and stretch them out from the entrance.

He suggested that I call Dr. John Klotz at UC Berkeley who has done extensive research with sugar baits for ants. From Dr. Klotz, I learned that in his tests, he found that 5 percent borates in sugar water was repellent to Argentine ants and that while 1 percent took longer, it was more effective. Klotz stressed the importance of having enough liquid to feed a mature colony of multiqueen ant species. He cited work done by Dr. Rust in which he found that one ant consumes its body weight each day, .3 mg. When dealing with hundreds of thousands of ants, it is easy to run out of food and that is when the ants enter homes in search of more food. My suggestion is for PCOs to be prepared to set out more than one bait station if the problem is with a super colony of ants and to visit the site often enough to refill the bait stations.

CONCLUSION. It would be foolhardy to attempt a "spray and pray" effort to try treat for ants without accurately identifying the species. Every service person should be equipped with Stoy Hedges’ Field Guide for the Management of Structure-Infesting Ants. It describes food preferences and biology and also has an easy-to-use identification guide for all common household species and help to locate the nest, which is still the best method of eliminating the source. Perhaps the technician will start turning over a board or a stone in the backyard to find the ant nest. It is a Myth Conception that all ant species are treated the same way.