HOUSEHOLD AND STRUCTURAL INSECTS Efficacy of Simulated Barrier Treatments Against Laboratory Colonies of Pharaoh Ant GRZEGORZ BUCZKOWSKI,1, 2 MICHAEL E. SCHARF,3 CATINA R. RATLIFF,1 1 AND GARY W. BENNETT J. Econ. Entomol. 98(2): 485Ð492 (2005) ABSTRACT Five selected insecticides were applied to four substrates and evaluated in laboratory studies for repellency and toxicity against the Pharaoh ant, Monomorium pharaonis (L.). We tested both repellent and nonrepellent formulations on outdoor (concrete and mulch) and indoor (ceramic and vinyl) substrates. Repellency was evaluated using a behavioral bioassay in which colonies were given a choice to leave the treated zone and move into empty nests provided in the untreated zone. We used a novel experimental design whereby ants walked on a Slinky coil suspended from a metal support frame, thus permitting a long foraging distance with a minimum use of space and resources. Cypermethrin, a repellent pyrethroid insecticide, resulted in colony budding, although the response was delayed. Toxicity of insecticides was evaluated as worker, queen, and brood mortality. The most effective treatment was Þpronil, which provided 100% reduction in pretreatment activity by 2 d posttreatment on both concrete and mulch. Chlorfenapyr was highly effective on both outdoor and indoor substrates. SigniÞcant substrate effects were observed with insecticides applied to nonabsor- bent substrates (ceramic tile), which performed better than insecticides applied to absorbent sub- strates (vinyl tile). Other highly absorbent materials (mulch and concrete), however, did not reduce insecticide efÞcacy. This is because ants relocated nests into and/or under these attractive nesting materials, thus increasing their exposure to toxic insecticide residues. Our results demonstrate efÞcacy of nonrepellent liquid insecticides as indoor treatments for the control of Pharaoh ants and possibly as exterior perimeter treatments. KEY WORDS Monomorium pharaonis, Pharaoh ant, repellency, residual insecticide THE PHARAOH ANT, Monomorium pharaonis (L.), is an may be initiated at any time. Traditionally, part of the introduced species that exhibits several tramp ant success and persistence of the Pharaoh ant had been characteristics such as generalist diet, polygyny, poly- attributed to its frequent budding habits (Edwards domy, large colony size, reproduction by budding, and 1986). Colony fragmentation may occur due to a wide close association with humans (Passera 1994). These range of biotic and abiotic factors; however, only lim- traits make colonies of Pharaoh ants successful invad- ited information exists on the factors responsible for ers of human built structures (Edwards and Baker inducing the budding behavior. Possible factors in- 1981, Edwards 1986) and also make them extremely clude overcrowding, response to weather (seasonal difÞcult to eradicate. Of the habits listed above, re- changes in a structureÕs central heating and cooling production by budding (sociotomy) is perhaps the system), physical disturbance, dietary change (deple- most critical to the success of Pharaoh ants. Although tion of or discovery of new resource), or chemical the majority of ant species disperse and start new disturbance (application of a repellent pesticide). colonies by individual females after a mating ßight, Traditionally, applications of repellent spray insecti- Pharaoh ants mate in the nest and colony reproduc- cides have been alleged to be the major factor pro- tion occurs by fragmentation of mature colonies (Ed- moting fragmentation of colonies (Green et al. 1954, wards 1986). During budding, a reproductively com- Lee et al. 1999). However, no detailed experimental petent colony fragment migrates to a new location to data exist to either support or refute this claim. In establish a new nest (Peacock et al. 1955, Vail and addition, residual insecticides are usually ineffective Williams 1994), which may or may not remain in for complete colony elimination because they only association with the parent colony. Thus, new colonies affect foraging workers and fail to reach reproductive are created independently of gyne production and individuals (Lee et al. 1999). Recently, new classes of nonrepellent pesticide 1 Department of Entomology, Purdue University, West Lafayette, chemistries have become available for urban pest con- IN 47907Ð2089. trol. The phenyl pyrazoles (Þpronil) and the struc- 2 Corresponding author, e-mail: [email protected]. 3 Entomology and Nematology Department, P.O. Box 110620, Uni- turally similar pyrroles (chlorfenapyr) are both non- versity of Florida, Gainesville, FL 32611Ð0620. repellent residual insecticides that have proven 0022-0493/05/0485Ð0492$04.00/0 ᭧ 2005 Entomological Society of America 486 JOURNAL OF ECONOMIC ENTOMOLOGY Vol. 98, no. 2 Fig. 1. Experimental design. Three plastic trays were connected by steel coils suspended from a metal support frame. The length of the coil between any two trays was 100 feet. Nest containing the colony was placed in the center tray and surrounded by treated surfaces. Alternative nesting trays were provided on either side. effective against a variety of pests of public and med- red acetate sheets to create the darkened conditions ical importance (Scott and Wen 1997, Ameen et al., preferred by the ants. Plastic spacers were inserted 2000). between the nest ßoor and the covering to restrict the The goals of this study were two-fold. Our main ants to a monolayer to facilitate counting of the various objective was to compare the efÞcacy of barrier treat- castes and developmental stages. When the nests were ments of reportedly nonrepellent insecticides (Þpro- observed to contain Ϸ20 queens, 80Ð90 1-cm2 grid nil and chlorfenapyr) to ones that are thought to be squares of brood (counted by overlaying a grid over repellent (synthetic pyrethroids). We hypothesized the nest and marking the outline of the brood), and that nonrepellent insecticides will be associated with Ϸ4,000 workers, single plates were transferred to the greater mortality via direct and indirect (horizontal center tray of the experimental conÞguration shown transfer) exposure to the active ingredient (e.g., Buc- in Fig. 1. zkowski and Schal 2001). In contrast, repellent treat- The experimental setup consisted of three 38 by ments will cause lower mortality due to colony relo- 50-cm Fluon-coated plastic trays connected by steel cation (budding) once the insecticide is detected. Our (Slinky, James Industries, Inc., Hollidaysburg, PA) second objective was to evaluate the efÞcacy of re- coils suspended from a metal support frame (Fig. 1). sidual insecticides on a variety of outdoor and indoor The length of the coil between any two trays was 100 substrates. Previous studies emphasized the impor- feet, and previous work in our laboratory has shown tance of surface type on insecticide efÞcacy (Chad- that Pharaoh ants will routinely traverse this distance wick 1985, Knight and Rust 1990, Osbrink and Lax without difÞculty (Ratliff and Bennett 2003). Empty 2002) with nonporous substrates generally providing nests were placed in trays adjacent to the center tray. better, longer lasting control. We examined four sub- To promote initial exploration of the center tray and strates likely encountered by foraging Pharaoh ants: the coils, food was provided mid-way (25 feet) along two outdoor substrates (concrete and mulch) and two the coils immediately adjacent to the center plate. indoor substrates (nonabsorptive ceramic and absorp- Food placements consisted of boiled egg yolk, peanut tive vinyl tile). oil, 10% sucrose, and whole cricket provided three times a week. After a 7-d acclimation period, treated substrates Materials and Methods were placed on three sides of the nest in the center Laboratory Pharaoh ant colonies were maintained tray, 3 cm from the nest. We tested two types of at constant temperature and humidity in an environ- outdoor substrates and two types of indoor substrates. mentally controlled rearing and testing room (25 Ϯ Outdoor substrates were concrete pavers (20 by 10 by 1ЊC, 65% Ϯ 10% RH). Colonies were reared in 38 by 4 cm in height) or hardwood mulch (Western White 50-cm Fluon-coated trays (DuPont Polymers, Wilm- Wood Mulch, Menards Inc., Eau Claire, WI; arranged ingtom, DE) on a regular diet of 10% sucrose, whole in aluminum foil trays 20 by 10 by 4 cm in height). cricket, peanut oil, and boiled egg yolk. Nests were Indoor substrates were ceramic (i.e., nonabsorptive plastic dishes Þlled with moist plaster. Experimental surface) and vinyl (i.e., absorptive surface) tile, both colony units were obtained by placing empty nests (9 10 by 10 cm by 0.5 cm in height. Five different liquid cm in diameter) in colony rearing trays for voluntary spray insecticides were examined (Table 1), although colonization by the ants. The nests were covered with not all insecticides were tested on all four substrates. April 2005 BUCZKOWSKI ET AL:COLONY BUDDING IN PHARAOH ANT 487 Table 1. Insecticides and active ingredients used in the study Insecticide trade Active Application rate Substrate Insecticide class Manufacturer name ingredient (␮g/cm2) tested on Cinnamite Cinnamaldehyde Aldehyde Mycotech, Butte, MT 12,973.0 Ceramic, vinyl Demon EC Cypermethrin Type II pyrethroid Syngenta Crop Protection 3.0 Ceramic, vinyl Inc., Greensboro, NC Phantom Chlorfenapyr Pyrrole BASF Corp, Research 34.5 Concrete, mulch, Triangle Park, NC ceramic, vinyl Talstar F Bifenthrin Type I pyrethroid FMC Corp., Philadelphia, PA 2.6 Concrete, mulch