CARPENTER ANT MORTALITY IN LABORATORY TESTS WHEN EXPOSED TO WOOD TREATED WITH ACZA

Carpenter ants have long been recognized as structurally damaging in the northern United States, Canada, and northern Europe (Hansen and Akre 1990, Wallin and Schroeder 1994). In many other parts of North America and Europe, carpenter ants are classified as nuisance pests. The categorization of either nuisance or structurally damaging is dependent, in part, upon the species involved (Hansen and Akre 1994, Hansen 1995). A total of 23 species of Camponotus has been recorded in North America invading structures in one of these categories. Some of these species attack only decayed wood; others will attack sound wood. Nests are made in standing and downed timber, in stumps, and in wood used in structures. Due to these nesting activities, carpenter ants have become a major economic problem in wooden structures.

The only attempt to define the total scope of carpenter ant infestations was made by Hansen and Akre 1985 in Washington State. Estimates were made separately for the eastern and western parts of the state. Western Washington provides a more amenable environment for carpenter ants than eastern Washington in that temperature ranges are narrower and precipitation and relative humidity are much higher. Conservative estimates in 1985 were 43,800 or 3.3% of the homes in western Washington were treated annually for carpenter ants compared to 1,400 or 0.32% of the homes in eastern Washington. Contacts with Extension personnel and pest control operators indicate that carpenter ants are a leading concern to homeowners throughout at least the northern tier of states and in southern Canada.

Carpenter ants, genus Camponotus , belong to the subfamily Formicinae, which is characterized by a circular anal orifice surrounded by a fringe of hair. Carpenter ant workers are recognized by the thoracic dorsum, which is evenly convex when viewed from the side. Damaging species occurring in North America include Camponotus modoc Wheeler, C.vicinus Mayr, C.pennsylvanicus (DeGeer), C.herculeanus (L.), C. abdominalis (Buckley). In Europe, the damaging species include C.herculeanus and C.lignaperda Latr .(Hansen and Akre 1993).

Unlike termites, which have symbiotic microorganisms in their midgut to aid in the digestion of cellulose, carpenter ants do not ingest wood. Instead, they remove wood with their mandibles to excavate brood chambers from the wood matrix and then deposit these wood chips away from their galleries. Carpenter ants also excavate tunnels to be used as runways to foraging arenas and satellite locations.

Colony size varies with species, latitude, and queen number. Larger colonies are reported in the northern latitudes of North America. The largest colony sizes (100,000 workers) have been reported for C.vicinus , which is polygynous. Colonies of C. modoc in the Pacific Northwest of the United States have been collected with 50,000 workers (Akre et al. 1994a). Most species of carpenter ants are monogynous but may contain additional non-inseminated queens that produce males. Established carpenter ant colonies are partitioned into parent or main colonies and satellite colonies, which are extensions of the main colony (Hansen and Akre 1985, Akre et al. 1995a). The parent colony, which contains the queen and workers, is located in an area with high humidity. The presence of eggs, larvae, pupae, and winged reproductives is dependent on seasonal development (Hansen and Akre 1985, Hansen 1993). The satellite colonies contain workers and depending upon seasonal development may contain mature larvae, pupae and winged reproductives. Satellite colonies are found in warmer areas with less humidity than the parent colony. These conditions enhance larval and pupal development. Numbers of satellite colonies found within structures range from 2 to 25. Both main and satellite colonies excavate wood for brood chambers and runways.

Carpenter ant infestations are controlled by the integration of management techniques involving cultural and chemical controls (Akre and Hansen 1990). The prevention of structural infestations in areas of high carpenter ant activity is the most obvious objective.

Wood treated with the water-borne preservative ACZA (Ammoniacal Copper Zinc Arsenate) was effective in preventing the attack of Formosan subterranean termite, Coptotermes formosanus Shiraki in tests in Hawaii (Tamashiro 1988). The objective of this study was to determine if ACZA treated wood is effective in preventing or repelling attacks by carpenter ants. Two sets of tests included (1) newly treated and untreated wood and (2) weathered treated and untreated wood.

The treatment of lumber or poles with the water-borne preservative ACZA (Ammoniacal Copper Zinc Arsenate) was extremely effective in preventing and repelling attack by carpenter ants even when this lumber is used adjacent to untreated lumber. Ants were killed when they came in contact with this material and individual ants were not repelled from contact with the treated surfaces. No differences were observed in the percent mortality of the ants when comparing to the different levels of ACZA retention and to the amount of treated lumber in the test chamber.

The precise mode of action of ACZA in killing the ants is not known. In the brief period of time that ants were exposed to the treated wood, very few attempts were made in excavations. As ants constantly groom themselves, the preservative is probably ingested after direct contact with the treated wood.

Treated weathered poles also were extremely effective in preventing and repelling attack by carpenter ants.