Carpenter ants are slowly being recognized by the structural pest control industry as the principal insects causing damage to structures in the northern tier of states in the U.S. and in southern Canada. Previously, carpenter ants were regarded — and still are by many — strictly as nuisance pests of houses and other structures. It has also been asserted that these ants nest only in structures damaged by water leaks that result in decay. This concept, while expounded by many, is erroneous (see References: Anonymous 1990).
As far back as 1918, S.A. Graham, in studies conducted in Minnesota, showed that carpenter ants were severe pests of standing forest trees, primarily cedar (Graham 1918). However, most studies of carpenter ants were concerned only with the biology of the various species, with little consideration given to the potential economic damage they might cause (Pricer 1908, Sanders 1964). However, research on carpenter ants that was started in the state of Washington and expanded into Minnesota (Hansen and Akre 1985) indicates that carpenter ants are indeed serious structural pests.
A PROFILE. Carpenter ants are members of the genus Camponotus that excavate wood or other fibers to make cavities for their nests. Camponotus is a large genus with many species, but few Camponotus species are con-sidered carpenter ants, and fewer still are regarded as pests that will infest structures.
The biology and habits of structurally damaging species of carpenter ants are similar throughout North America. The concept of the colony as given by Sanders (1964) is correct for at least several large colony species. He showed that carpenter ants usually have a main colony — the parent colony — and one or several satellite colonies. The parent colony contains the queen and usually has large amounts of brood including eggs and small larvae. Satellites never have eggs or small larvae, only workers, mature larvae, and pupae.
Carpenter ant colonies have two peaks of activity during a typical season in the northern U.S. and southern Canada. Colonies break diapause between April and June (depending on weather and elevation), when the queen begins laying eggs. The developing larvae"drive" the colony, and peak foraging by the workers ensues to feed the rapidly developing larvae during June and July. A second peak of activity occurs in mid-August, when the queen lays eggs again. This activity period is shorter and less intense.
The colony enters into diapause during September or October. The overwintering brood overwinters as larvae and completes development in late winter (Hansen and Akre 1985). Reproductives (male and female swarmers) issue from the nest to fly, mate, and attempt to initiate new colonies during the first warm days of spring. This swarming activity could occur anywhere between January and June, depending on weather conditions and locale.
Carpenter ant colonies are comprised of workers of various sizes, from small ("minor") workers to much larger ("major") workers. In addition, the colony has a foundress queen, and in the fall, winter, and early spring has two additional castes, the males and females (new queens).
At any given moment, fewer than 10% of a carpenter ant colony's workers will be out foraging for food. This food consists of honeydew from various homopterous insects (i.e. aphids, scales), and carpenter ants also kill a number of insects and bring them back to the colony for larval food. Carpenter ants are primarily nocturnal, and peak foraging activity occurs at night. Foraging times change over the season; peak foraging activity can occur from dusk until 4 a.m.
Carpenter ants establish foraging trails that are easily visible when they extend across lawns. All vegetation is removed for ease of travel. Trails are also marked with a trail pheromone, so the ants have no difficulty following them in the dark. The ants can also navigate by a light compass response — to the sun during the day, or to the moon or even to bright artificial lights such as streetlights at night.
Camponotus modoc and Camponotus pennsylvanicus usually nest in standing dead or live trees. Some other species, particularly Camponotus vicinus, usually nest in small logs lying on the soil surface, and their nests usually extend into the soil.
Satellite colonies enter structures whenever carpenter ants require a drier or warmer environment for the development of their larvae. All carpenter ants will excavate dry, sound wood, but they also excavate wood that has been damaged by water. The latter is softer and easier to excavate, and some researchers believe that carpenter ants are found only in structures with water-damaged, rotten wood. This is not true. However, a somewhat similar situation has arisen with the increased use of foam core panels in building houses. The ants prefer to excavate in the soft foam material, and these infestations are a significant problem to homeowners.
THE CULPRITS. The principal carpenter ant species responsible for damage in the western U.S. are C. modoc Wheeler and C. vicinus Mayr. The former species causes about 75% of the damage (Hansen and Akre 1985). In the eastern United States, the principal wood-destroying species are C. pennsylvanicus (DeGeer), C. novaeboracensis (Fitch) and C. herculeanus (L.). C. pennsylvanicus is a sister species to C. modoc, and is apparently responsible for most structural damage in the east (Smith 1965). It also causes damage to standing live cedar (Graham 1918), and to several species of shade trees (Fowler and Parrish 1982).
Structural damage by carpenter ants is not well documented except for the western U.S. (Hansen and Akre 1985). However, the areas in which they have been reported as a serious problem extend from Washington and Oregon on the West Coast to New Brunswick (Sanders 1964) and New York on the East Coast. Structural damage is also recognized as potentially severe by members of the pest control industry in the east (Anonymous 1990). Thus, carpenter ants are apparently a problem in the entire tier of northern states, and this problem extends into Virginia in the south.
In the state of Washington, at least 42,000 structures are treated annually for carpenter ants (Hansen and Akre 1985; estimated at 50,000 as of 1994), while Fowler (1986) showed that these ants cause millions of dollars of damage in the northeast. Thus, the concept of carpenter ants only as nuisance pests is changing. The actual dollar losses are not well documented, nor are the damages caused, but they are considerable.
Even if carpenter ants were not structural pests, it has been reported that 83.5% of homeowners dislike having any insects found in their homes (Byrne et al. 1984), and carpenter ants are usually considered serious pests by homeowners regardless of whether or not they caused structural damage (Dukes 1989). Treatment of colonies of carpenter ants by professionals usually costs between $100 and $500 (Berns1989), although some treatments have exceeded $5,000.
BUILDING A CASE. The evidence that carpenter ants are serious structural pests attacking sound wood is readily available in the state of Washington (Hansen and Akre 1985), where carpenter ants — primarily C. modoc — attack many new homes built in wooded areas in and around Seattle. They are also serious structural pests in the drier eastern portions of Washington such as Pullman (18 to 22 inches of rainfall annually), where firewood infested by C. modoc is brought in from Idaho.
Two examples will illustrate damage that can be found.
• An older home was being remodeled, and the inner wall boards were completely removed. Most of the wall studs along a 20-foot wall were tunneled by carpenter ants. The most seriously damaged wood was so extensively tunneled that an 8-foot-long two-by-four weighed less than 2 pounds. This tunneling also extended into the ceiling so that the owner fell through the ceiling (one leg) while he was showing us the damage.
• Damage was also extensive in Bryan Hall on the Washington State University campus. The oak flooring in this building was damaged by carpenter ants and dry rot. The main colony was found about 300 feet away in a wooden retaining wall that had been extensively tunneled and had to be replaced. The total cost was more than $20,000. Portions of the president's house on the WSU campus have also been extensively damaged by carpenter ants.
Similar examples of damage by carpenter ants are common in Minnesota, from Minneapolis northward to the Canadian border. A home near Grand Rapids, Minn. was damaged by a colony of C. pennsylvanicus that excavated a wall and supporting timbers separating a bedroom from a kitchen. This damage cost more than $5,000 to repair (in 1988), even with the homeowner doing all the work. All damage involved solid wood, with no evidence of decay or water damage.
Another home in the same area had sawdust piles 8 to 10 inches in height from carpenter ant excavations in the basement and in the attic, but no effort was made to access the damaged areas. There was no evidence of water damage in either instance. We have investigated other examples of extensive damage to structures by carpenter ants, mostly in the Grand Rapids area. (This also includes damage from C. herculeanus and C. novaebora-censis.)
CONTROL PROCEDURES. Control of carpenter ants ideally starts with a survey of the lot on which a home will be built, especially if the lot is heavily wooded. Colonies of carpenter ants located in stumps and trees must be removed or destroyed. Then, as the house is being built, an insecticidal dust can be applied into the wall voids before the insulation goes in and the wall board goes on. Also, the structure should be built so that few or no access holes are available to the ants (Akre et al. 1990).
Since carpenter ants have a main or parent colony that is usually outside in a stump or tree, with satellite colonies inside the structure acting as a nuisance and/or causing damage, it is essential that a thorough, painstaking attempt be made to locate the parent colony. Thus, remedial control includes first finding and destroying the parent colony (Hansen and Akre 1985, Akre et al. 1994). This is accomplished by following the ants on their trails from the house, as parent and satellite colonies always maintain communication and contact by means of worker traffic between the colonies. Since carpenter ants are nocturnal, locating the parent colony is usually done at night.
Once the parent colony has been eliminated, the satellite colony inside the house can be controlled by applying a dust formulation of insecticide into the wall voids via electrical and water pipe outlets (Caruba 1988). A large section of a structure with no access via electrical lines can be drilled (with a 1/8 inch bit) for insertion of a wand from the dust applicator. However, this is seldom necessary. Crawl spaces should be treated inside and out with a perimeter spray (liquid). This spray should extend up the wall and out onto the soil about 12 inches. Particular attention should be given to the areas where ant trails enter and exit the structure. The ants must cross this insecticidal barrier on their way to the outside, and the colony will be quickly controlled (Akre et al. 1990).
We developed a control program for carpenter ants that greatly reduces the amount of insecticide used while still providing excellent control. We have treated a number of structures with Tempo 0.1% Dust (cyfluthrin). The dust was usually applied with an Actisol duster, and all wall voids in a structure were treated using 3.2 ounces or less. If this duster was not available, a hand-held duster was used to apply 12 to 16 ounces of dust. Obviously, the Actisol application is preferred for uniform coverage and the use of much less insecticide. After the application of the dust, Tempo 20 WP was applied at a concentration of 0.05% as the perimeter spray. Ordinarily a 2-gallon compressed air sprayer was used to apply the spray, and 1 to 3 gallons were used (see table on page 60).
Dust applications are not only the most effective means for the control of carpenter ants; they also produce the least amount of environmental impact. With the degree of environmental conscientiousness rising and the growing numbers of people who are chemically or psychologically sensitive to the use of chemicals, dusts are more readily accepted. Comparison of the amount of active ingredient (A.I.) used in a dust application to the amount used in a wall injection of liquid shows a minimum of 60 times less A.I. issued in the dust application. For example, in the treatment of an average size home — 30 ´ 50 or 1,500 square feet — an average of 3.2 ounces of dust is used.
A dust treatment involves injecting dust behind switchplates and electrical outlet boxes after the covers have been removed, and along accessible water and sewer lines under plumbing fixtures. Using Tempo 0.1% Dust, the amount of A.I. used in the treatment is 0.003 ounce. If the same structure is treated by liquid wall injection, 0.25 ounce (0.05% Tempo 20 WP) or 0.5 ounce (0.1%) of A.I. is used. This number is calculated by dividing the perimeter of the house (160 feet) by the stud spacing (1 foot 4 inches) and multiplying by 4 ounces (the amount injected per hole) to yield 480 ounces (3.75 gallons).
In typical tent fumigations, an even greater amount of A.I. is released into the environment. In an average size home(1,500 square feet), 20 pounds of A.I. is used.
In comparing Tempo to other chemicals used in carpenter ant control, the calculations show similar differences when comparing dust to liquid wall injections. Thus, when using a 1% dust (Brand X), 0.03 ounce is used instead of 0.003 ounce (Tempo 0.1% Dust), and 2 ounces of 0.5% WP (Brand X) is used instead of 0.25 ounce of Tempo WP used at 0.05%. Thus, the use of Tempo formulations are effective at 1/10 the amount of AI as that used in other materials.
Perimeter sprays are most effective when correctly applied under the lower edge of siding where ants most often travel on the exterior of the structure. This can be effectively accomplished with a compressed air sprayer and the use of 1 to 2 gallons of material. Tempo WP at 0.05% uses 0.07 ounce of AI per gallon, as compared to other materials at 0.25% which use 0.34 ounce per gallon, and those at 0.5% which use 0.67 ounce per gallon.
However, many operators use power sprayers to apply 25 to 30 gallons of spray for the perimeter. The use of hand sprayers is preferable over high pressure sprayers because a lower volume of material is applied, the selective site is most effectively covered, and less environmental damage is incurred. These applications are also much cheaper and more environmentally sound.
Tempo 0.1% Dust had been found to be an excellent wall void treatment, as it quickly destroys carpenter ants. In addition, this formula of Tempo is very irritating to carpenter ants and will immediately flush them out of voids. Total control usually occurred within a week, with the highest mortality occurring on the first day. Carpenter ants are quite hairy and easily pick up dust particles. Grooming distributes the dust within the colony. Liquids, of course, should never be used in wall voids due to the fire hazard from potential electrical shorts (see specimen label for Tempo 20 WP). Tempo 0.1% Dust can be applied with a hand-held duster in very low amounts in structures, and the amounts used can be lessened if an injector such as the Actisol power duster is used.
Of the 57 structures treated in our study, four structures that had no initial wall void treatment were retreated, and three were retreated after a void was missed. Those structures were retreated, and no ants were found the following year. The yard of one structure had many railroad tie retaining walls that contained at least two separate large colonies. The railroad ties were only partially treated, and the homeowners were told to remove the ties or control would never be complete.
Two structures that had some ants the year following initial treatment of a perimeter spray only were not retreated. Both of these were infested with C. essigi, mainly a kitchen nuisance pest that is very difficult to control by using the same techniques as for wood-destroying carpenter ant species. One structure was only partially treated in 1993, and ants were found in 1994 only in the untreated portion. In one case, the homeowner thought he saw ants, but a further inspection by us revealed none. The house had been initially treated by the homeowner with a hand duster in 1991, but was retreated in 1993 by us despite the lack of ants.
SUMMARY. Carpenter ants, while serious structural pests, can be readily and effectively controlled using the techniques outlined above. An effective dust formulation coupled with an effective perimeter spray can be used to control carpenter ants with a significant reduction in the amount of insecticide used. We urge PCOs to try this method. Roger D. Akre passed away in August 1994. He was a professor of entomology at Washington State University, Pullman, Wash. Laurel D. Hansen and Elizabeth A. Myhre are also with the Department of Entomology at WSU.
REFERENCES
• Akre, R. D. and L. D. Hansen. 1988. Carpenter ants. Proc. Nat. Conf. Urban Ent. 1988: 59-63
• Akre, R.D. , L.D. Hansen, and A.L. Antonelli. 1990.
• Carpenter ants: Their biology and control. Ext. Bull. 0818. Coop. Ext. Wash. State Univ. 6 pp.
• Akre, R.D., L.D. Hansen, and E.A. Myhre. Do you know where your parents are? Pest Control Technology. 22(5): 44, 46, 55, 58, 60, 64.
• Anonymous. 1990. Carpenter ants offer the PCO challenges and opportunities. Insectimes 12(2): 1-3.
• Berns, B. 1989. Properly pricing carpenter ant jobs. Pest Control Technology. 17(5): 34-36, 40.
• Byrne, D.N., E.H. Carpenter, E.M. Thoms, and S.T. Cotty. 1984. Public attitudes toward urban arthropods. Bull. Ent. Soc. Amer. 30(2): 40-44. Caruba, A. 1988. Insecticide dusts make a comeback. Pest Control Technology. 16(11): 44, 46.
• Dukes, J. III. 1989. Aspects of the biology, behavior, and economic importance of C. pennsylvanicus (DeGeer) and C. ferrugineous (Fabricius) (Hymenoptera: Formicidae). Thesis, Virginia Polytechnic Institute and State University. 90 pp.
• Fowler, H.G. 1986. Biology, Economics, and Control of Carp. Ants. Chapter 10, pp. 272-289. In S.B. Vinson, Ed. Economic Impact and Control of Social Insects. Praeger: NY. 421 pp.
• Fowler, H.G. and M.D. Parrish. 1982. Urban shade trees and carpenter ants. J. Arbocult. 8: 281-284.
• Graham, S.A. 1918. The carpenter ant as a destroyer of sound wood. Minn. State Ent. Rept. 17: 32-40.
• Hansen, L.D. and R.D. Akre. 1985. Biology of carpenter ants in Washington State (Hymenoptera: Formicidae: Camponotus). Melanderia 43: 1-62.
• Pricer, J.L. 1908. The life history of the carpenter ant. Biol. Bull. 14: 177-218.
• Sanders, C.J. 1964. The biology of carpenter ants in New Brunswick. Can. Ent. 96: 894-909.
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NOT JUST A REGIONAL PROBLEMThe following is a brief summary of some of the carpenter ant findings from five states in the midwestern and eastern U.S.: • Dr. William Lyon at Ohio State University showed carpenter ants were the No. 1 problem reported to cooperative extension between 1988 and 1994. • According to Jeff Hahn at Dial-U Insect and Plant Information Clinic, carpenter ants were the most commonly reported pest in Minnesota in 1987 and 1990 (dis-placed to No. 2 by boxelder bugs in 1988 and 1989). • Howard Russell, insect diagnostician at the Insect Diagnostic Laboratory, Michigan State University, showed that carpenter ants were No. 1 in 1981, No. 2 behind wasps and bees in 1979 and 1980, and No. 1 in 1988 and 1990. (Data for 1989 were unavailable.) • Carolyn Klass of the Cornell New York Insect and Plant Disease Diagnostic Laboratory collated data for annual reports on structural pests from 1986 to 1992; she found carpenter ants to be No. 1 by a wide margin. • Eric Day at the Virginia Tech Insect Identification Laboratory collated data showing carpenter ants were the No. 1 structural pest from 1987 to 1989, and were second to termites from 1990 to 1992. Latest from Pest Control Technology
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