Effect of horizontal transfer of barrier insecticides to control Argentine ants (Hymenoptera: Formicidae)

Horizontal transfer of three contact insecticides, bifenthrin, beta-cyfluthrin, and fipronil, was tested in laboratory colonies. Donor ants were exposed for 1 min to insecticide-treated sand substrates and placed with unexposed ant colonies at two different temperatures. Mortality was monitored to compare the ability of donors to transfer lethal doses of these insecticides to untreated individuals. Treated donor insects, live or dead, were added into colonies to determine the importance of donor behavior on lethal transfer. Fipronil was readily transferable between individuals, resulting in high mortality rates. Bifenthrin and beta-cyfluthrin were less transferable, exhibiting moderate-to-low mortality rates similar to the controls. Greater mortality occurred at 27-29 degrees C than at 21-23 degrees C for bifenthrin, but not the other treatments or controls. Colony mortality did not significantly increase when adding live donors, suggesting that necrophoresis was probably an important donor behavior in addition to grooming and trophallaxis on horizontal transfer.     

Horizontal transfer of insecticides in laboratory colonies of the Argentine ant (Hymenoptera: Formicidae)

Five insecticides used by urban pest management professionals for ant control and three experimental insecticides were tested to determine whether these insecticides were horizontally transferred among individuals in colonies of Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae). Ants were exposed to insecticide-treated sand for 1 min and then placed in a colony of untreated ants. Ants exposed to 20 and 40 ppm fipronil readily transferred the insecticide to other individuals in the colony, resulting in high mortality. Most of the transfer and subsequent mortality occurred within 4 d after exposure to treated ants. The other insecticides were not transferred, and ants exhibited mortality rates similar to that of the controls. Experiments in large foraging arenas demonstrated that necrophoresis was an important behavior facilitating the horizontal transfer of fipronil. When ants contacted contaminated corpses in the process of removing them to refuse piles, they received a lethal dose of fipronil and subsequently died. Fipronil-contaminated dead ants that were placed in the vicinity of the nest resulted in significantly higher mortality than did corpses placed in a distant foraging arena (30 cm away). Most of the dead ants accumulated in the vicinity of the nest rather than in the foraging arena, workers retrieving dead ants to refuse piles from the foraging arena. The position effect of insecticide-contaminated corpses relative to the nest and its implication for Argentine ant control are discussed.     

Determining the foraging range and origin of resurgence after treatment of Argentine ant (Hymenoptera: Formicidae) in urban areas

The foraging range and distribution of Argentine ant, Linepithema humile (Mayr), colonies in urban areas of southern California extended at least 61 m (200 feet) from feeding stations and structures. Ants were fed at 25% sucrose feeding stations containing 0.01% fluorescent brighter (FB28). Within 14 d, from 77-90% of the ants sampled next to the feeding stations were positive for FB28. The percentage of ants with FB28 declined gradually to approximately 55% 61 m away from the feeding station. The percentage of marked ants in the controls didn't change over the 4-wk-test period. There were approximately 290,000 ants visiting the monitored stations each night before treatments. The 0.0001% fipronil baits and 0.06% fipronil SC sprays provided significant reductions in at least 4 wk. The percentage of ants marked with FB28 decreased significantly in both bait and spray treatments over 4 wk suggesting that the resurgence of ants in treated areas were because of immigration from untreated areas. It is likely that much larger areas will need to be treated to control Argentine ants in urban settings, especially if baits are being used.     

Let them eat termites—prey‐baiting provides effective control of Argentine ants,Linepithema humile,in a biodiversity hotspot

Invasive ants threaten biodiversity, ecosystem services and agricultural systems. This study evaluated a prey‐baiting approach for managing Argentine ants in natural habitat invaded by Argentine ants. Blackmound termites (Amitermes hastatus) were topically exposed to fipronil and presented to Argentine ants (Linepithema humile). In laboratory assays, L. humile colonies were offered fipronil‐treated termites within experimental arenas. The termites were readily consumed, and results demonstrate that a single termite topically treated with 590 ng fipronil is capable of killing at least 500 L. humile workers in 4 days. Field studies were conducted in natural areas invaded by L. humile. Fipronil‐treated termites scattered within experimental plots provided rapid control of L. humile and ant densities throughout the treated plots declined by 98 ± 5% within 21 days. Results demonstrate that the prey‐baiting approach is highly effective against L. humile and may offer an effective alternative to traditional bait treatments. Furthermore, prey‐baiting offers environmental benefits by delivering substantially less toxicant to the environment relative to current control methods which rely on commercial bait formulations and may offer greater target specificity.     

Development of virtual bait stations to control Argentine ants (Hymenoptera: Formicidae) in environmentally sensitive habitats

A novel bait station referred to as a virtual bait station was developed and tested against field populations of the invasive Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), at White Beach, Camp Pendleton, in Oceanside, CA. White Beach is a nesting habitat for an endangered seabird, the California least tern (Sterna antillarum browni Mearns). The beach is heavily infested with Argentine ants, one of the threats for the California least tern chicks. Conventional pest control strategies are prohibited because of the existence of the protected bird species and the site's proximity to the ocean. The bait station consisted of a polyvinyl chloride pipe that was treated on the inside with fipronil insecticide at low concentrations to obtain delayed toxicity against ants. The pipe was provisioned with an inverted bottle of 25% sucrose solution, then capped, and buried in the sand. Foraging ants crossed the treated surface to consume the sucrose solution. The delayed toxicity of fipronil deposits allowed the ants to continue foraging on the sucrose solution and to interact with their nestmates, killing them within 3-5 d after exposure. Further modification of the bait station design minimized the accumulation of dead ants in the sucrose solution, significantly improving the longevity and efficacy of the bait station. The virtual bait station exploits the foraging behavior of the ants and provides a low impact approach to control ants in environmentally sensitive habitats. It excluded all insects except ants, required only milligram quantities of toxicant, and eliminated the problem of formulating toxicants into aqueous sugar baits.     

Effects of interspecific competition between two urban ant species, Linepithema humile and Monomorium minimum, on toxic bait performance

We evaluated the effects of interspecific competition on ant bait performance with two urban pest ants, the Argentine ant, Linepithema humile (Mayr), and the little black ant, Monomorium minimum (Buckley). In a laboratory study, the impact of a solid sulfluramid bait on M. minimum was diminished when L. humile were present, whereas the presence of M. minimum reduced the performance of a liquid fipronil bait against L. humile. Argentine ants were not adversely affected by sulfluramid bait at any time, whereas M. minimum was unaffected by fipronil bait until 14 d of exposure. In field studies measuring diel foraging activity, M. minimum seemed to delay L. humile foraging to food stations by approximately 30 min during summer 2001. However, L. humile subsequently recruited to food stations in very high numbers, thereby displacing M. minimum. L. humile visited food stations over an entire 24-h period, whereas M. minimum was only observed visiting food stations during daylight hours. Adjusting the timing of bait placement in the field may minimize any negative effects of interspecific competition between these two species on toxic bait performance.     

Trap-mulching Argentine ants

Argentine ant, Linepithema humile (Mayr), management is constrained, in large part, by polydomy where nestmates are distributed extensively across urban landscapes, particularly within mulch. Management with trap-mulching is a novel approach derived from trap-cropping where ants are repelled from a broad domain of nest sites to smaller defined areas, which are subsequently treated with insecticide. This concept was field-tested with mulch surrounding ornamental trees replaced with a narrow band of pine (Pinus spp.) needle mulch (trap) within a much larger patch of repellent aromatic cedar (Juniperus spp.) mulch. After ants reestablished around the trees, the pine needle mulch band was treated with 0.06% fipronil (Termidor). Poor results were obtained when the trap extended from the tree trunk to the edge of the mulched area. When the trap was applied as a circular band around the tree trunk reductions in the number of foraging ants were recorded through 14 d compared with an untreated mulch control, but not for longer periods. Reductions in the number of ant nests within mulch were no different between the trap mulch and any of the other treatments. We conclude that trap-mulching offers limited benefits, and that successful management of Argentine ants will require implementation of complementary or perhaps alternative strategies.     

Retrieval of granular bait by the Argentine ant (Hymenoptera: Formicidae): effect of clumped versus scattered dispersion patterns

Argentine ants, Linepithema humile (Mayr), use mass recruitment foraging, with clumped prey items being retrieved more efficiently than dispersed prey. However, in prior field experiments, granular baits, whether dispensed in containers or broadly scattered, had a similar impact on Argentine ant populations. In laboratory experiments, granular insecticide bait was encountered faster by Argentine ant workers and more granules were initially returned to the colony when the granules were scattered versus clumped. After 2 h, granules from both dispersion patterns were retrieved equally. Our results suggest that Argentine ant colonies adjust their foraging patterns to resources of different quality (prey versus bait). Also, foraging activity patterns for bait in the laboratory are consistent with prior field results demonstrating no efficacy advantages to discrete granular bait placements.     

Parasitoids deter foraging by Argentine ants (Linepithema humile) in their native habitat in Brazil

The Argentine ant, Linepithema humile, has invaded sites across Africa, Australia, Europe, and North America. In its introduced ranges it eliminates native ants and tends agricultural pests. Few studies have examined the ecology of Argentine ants in their native habitat. This study examined the effects of parasitoid flies, genus Pseudacteon, on the foraging behavior of Argentine ants in part of their native range in southern Brazil. Pseudacteon parasitoids commonly attacked Argentine ants, but not other ant species, in daylight at temperatures above 18°C. Argentine ants abandoned food resources and returned underground in the presence of parasitoids. Parasitoid attack rates diminished as Argentine ants retreated underground. Where parasitoids were present, Argentine ants were abundant at food resources only during times of day when parasitoids were inactive. Where parasitoids were absent, Argentine ants were abundant at food resources throughout the day. Overall, the presence of parasitoids explained observed variation in Argentine ant foraging far better than temperature, although temperature had some effect. The results suggest that Pseudacteon parasitoids inhibit the ability of Argentine ants to gather food resources in their native habitat in Brazil. Received: 11 December 1997 / Accepted: 12 June 1998     

Mechanisms of dispersed central-place foraging in polydomous colonies of the Argentine ant

Many species of ants occupy multiple nests, a condition known as polydomy. Because of their decentralized structure, polydomous colonies may be removed from some of the constraints associated with classic central-place foraging. We used laboratory and field experiments to assess the mechanisms involved in dispersed central-place foraging in polydomous colonies of the Argentine ant Linepithema humile, a widespread invasive species. Both in the laboratory and in the field, Argentine ants established new nests at sites located near food. Laboratory colonies of L. humile redistributed workers, brood and resources among nests in response to the spatial heterogeneity of food resources. In addition, laboratory colonies formed recruitment trails between nests in the context of foraging, providing a mechanism for the transport of material between nests. This highly flexible system of allocating nests, workers and brood throughout a colony's foraging area potentially increases foraging efficiency and competitive ability. The importance of polydomy as a determinant of competitive ability is underscored by its prevalence among ecologically dominant ants, including most, if not all, highly invasive species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Influence of temperature on rate of uptake and subsequent horizontal transfer of [14C]fipronil by eastern subterranean termites (Isoptera: Rhinotermitidae)

The effect of temperature on [14C]fipronil uptake and transfer from donor (D) to recipient (R) Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) workers was evaluated. Test chambers used in the fipronil uptake study were constructed from petri dishes containing autoclaved soil treated with 1 ppm [14C]fipronil (1.14 microCi of total radioactivity per petri dish), distilled water, and R. flavipes workers. Test chambers were held in environmental growth chambers preset at 12, 17, 22, 27, and 32 degrees C. For the fipronil transfer study, donor termites stained with Nile blue-A were exposed to soil treated with 1 ppm [14C]fipronil for 2 h. Donors were then combined with unexposed recipient termite workers at either 1D:5R, 1D:10R, or 1D:20R ratios. Test chambers consisted of a nest and feeding chamber connected by a piece of polyethylene tube and held in growth chambers at 12, 17, 22, 27, and 32 degrees C. Worker termites were sampled over time and the amount of [14C]fipronil present was measured by scintillation counting. Some degree of uptake and transfer occurred at all temperatures and ratios in this study. The highest level of uptake occurred by termites held at 22-32 degrees C, followed decreasingly by 17 and 12 degrees C. Maximum transfer of [14C]fipronil occurred at the higher ratios (1:5 > 1:10 > 1:20) of donors to recipients. Data presented in this study suggest that temperature is one of the key factors affecting the rate of uptake and subsequent horizontal transfer of [14C]fipronil in subterranean termites.     

Toxicity of seven termiticides on the formosan and eastern subterranean termites

Using both topical application and substrate (sand) treatments the toxicities of seven new generation soil termiticides were evaluated to determine the LD50 and LC50 against two economically important subterranean termite species, eastern subterranean termite, Reticulitermes flavipes (Kollar), and Formosan subterranean termite, Coptotermes formosanus Shiraki. The lethal dose toxicity (LD50) rankings for R. flavipes from highest to lowest were: fipronil > bifenthrin > chlorantraniliprole > cyantraniliprole > imidacloprid > chlorfenapyr > indoxacarb; the rankings for C. formosanus were fipronil > imidacloprid > chlorantraniliprole > cyanthraniliprole> bifenthrin > chlorfenapyr > indoxacarb. The respective lethal concentration toxicity (LC50) rankings were fipronil > bifenthrin > chlorfenapyr > indoxacarb > cyantraniliprole > chlorantraniliprole > imidacloprid for R. flavipes; and fipronil > chlorfenapyr > bifenthrin >imidacloprid > cyantraniliprole > chlorantraniliprole > indoxacarb for C. formosanus. The study provides an opportunity to directly compare toxicity, action speed, and bioavailability among this group of newer generation soil termiticides.     

The Argentine ant persists through unfavorable winters via a mutualism facilitated by a native tree

Mutualisms and facilitations can fundamentally change the relationship between an organism's realized and fundamental niche. Invasive species may prove particularly suitable models for investigating this relationship as many are dependent on finding new partners for successful establishment. We conducted field-based experiments testing whether a native tree facilitates the successful survival of the invasive Argentine ant, Linepithema humile (Mayr), through unfavorable winter conditions in the southeastern United States. We found Argentine ant nests aggregated around the native loblolly pine, Pinus taeda L., during the winter months. The bark of this tree absorbed enough radiant solar energy to reach temperatures suitable for Argentine ant foraging even when ambient temperatures should have curtailed all foraging. Conversely, foraging ceased when the trunk was shaded. The sun-warmed bark of this tree gave the Argentine ant access to a stable honeydew resource. Argentine ants were not found on or near deciduous trees even though bark temperatures were warm enough to permit Argentine ant foraging on cold winter days. Augmenting deciduous trees with sucrose water through the winter months lead to Argentine ant nests remaining at their base and Argentine ants foraging on the tree. The Argentine ant requires both foraging opportunity and a reliable winter food source to survive through unfavorable winter conditions in the southeastern United States. The loblolly pine provided both of these requirements extending the realized niche of Argentine ants beyond its fundamental niche.     

Exploitation and interference competition between the invasive Argentine ant,Linepithema humile,and native ant species

Interactions between the invasive Argentine ant, Linepithema humile, and native ant species were studied in a 450-ha biological reserve in northern California. Along the edges of the invasion, the presence of Argentine ants significantly reduced the foraging success of native ant species, and vice versa. Argentine ants were consistently better than native ants at exploiting food sources: Argentine ants found and recruited to bait more consistently and in higher numbers than native ant species, and they foraged for longer periods throughout the day. Native ants and Argentine ants frequently fought when they recruited to the same bait, and native ant species were displaced from bait during 60% of these encounters. In introduction experiments, Argentine ants interfered with the foraging of native ant species, and prevented the establishment of new colonies of native ant species by preying upon winged native ant queens. The Argentine ants' range within the preserve expanded by 12 ha between May 1993 and May 1994, and 13 between September 1993 and September 1994, with a corresponding reduction of the range of native ant species. Although some native ants persist locally at the edges of the invasion of Argentine ants, most eventually disappear from invaded areas. Both interference and exploitation competition appear to be important in the displacement of native ant species from areas invaded by Argentine ants.     

Argentine ants displace floral arthropods in a biodiversity hotspot

Argentine ant (Linepithema humile (Mayr)) invasions are often associated with the displacement of ground‐dwelling arthropods. Argentine ant invasions can also exert other effects on the community through interactions with plants and their associated arthropods. For example, carbohydrate resources (e.g. floral or extrafloral nectar) may influence foraging behaviour and interactions among ants and other arthropods. In South Africa's Cape Floristic Region, Argentine ants and some native ant species are attracted to the floral nectar of Leucospermum conocarpodendron Rourke (Proteaceae), a native tree that also has extrafloral nectaries (EFNs). Despite having relatively low abundance in pitfall traps, Argentine ants visited inflorescences more frequently and in higher abundance than the most frequently observed native ants, Camponotus spp., though neither native nor Argentine ant floral foraging was influenced by the EFNs. Non‐metric multidimensional scaling revealed significant dissimilarity in arthropod communities on inflorescences with Argentine ants compared to inflorescences with native or no ants, with Coleoptera, Diptera, Hymenoptera, Arachnida, Orthoptera, and Blattaria all being underrepresented in inflorescences with Argentine ants compared to ant‐excluded inflorescences. Native honeybees (Apis mellifera capensis Eschscholtz) spent 75% less time foraging on inflorescences with Argentine ants than on inflorescences without ants. Neither Argentine ant nor native ant visits to inflorescences had a detectable effect on seed set of Le. conocarpodendron. However, a pollen supplementation experiment revealed that like many other proteas, Le. conocarpodendron is not pollen‐limited. Flower predation was negatively associated with increased ant visit frequency to the inflorescences, but did not differ among inflorescences visited by native and Argentine ants. Displacement of arthropods appears to be a consistent consequence of Argentine ant invasions. The displacement of floral arthropods by Argentine ants may have far‐reaching consequences for this biodiversity hotspot and other regions that are rich in insect‐pollinated plants.     

Response of Argentine ants and red imported fire ants to permethrin-impregnated plastic strips: foraging rates, colonization of potted soil, and differential mortality

This study investigated the effects of the permethrin-impregnated plastic on ant mortality and foraging rates, and tested its potential for preventing ants from colonizing potted soil. Direct exposure to the plastic for as short as 1 min caused significant mortality of both red imported fire ants, Solenopsis invicta Buren, and Argentine ants, Linepithema humile (Mayr); however, red imported fire ants were more susceptible than Argentine ants. Knockdown of virtually all ants initially occurred within 15 min after exposure. However, some moribund ants recovered from the effects within 24 h. For example, after 1 min of direct exposure to the permethrin-impregnated plastic, 70% of Argentine ants and 5% of red imported fire ants recovered from the treatment. In established colonies of Argentine ants, significantly fewer ants foraged for food up posts treated with the plastic compared with untreated posts. In addition, colonies responded to introduction of the treatment by significantly reducing their overall foraging rates, even on untreated posts. When pots filled with moistened soil were introduced into established ant colonies, 82% of Argentine ants and 99% of red imported fire ants moved into the soil. In contrast, when a 1-cm-wide coil of the plastic was placed under the pot, no ants moved into the soil. The potential for use of these materials in nursery production is discussed.     

Trail Pheromone of the Argentine Ant,Linepithema humile (Mayr) (Hymenoptera: Formicidae)

The Argentine ant (Linepithema humile) is recognized as one of the world''s most damaging invasive species. One reason for the ecological dominance of introduced Argentine ant populations is their ability to dominate food and habitat resources through the rapid mobilization and recruitment of thousands of workers. More than 30 years ago, studies showed that (Z)-9-hexadecenal strongly attracted Argentine ant workers in a multi-choice olfactometer, suggesting that (Z)-9-hexadecenal might be the trail pheromone, or a component of a trail pheromone mixture. Since then, numerous studies have considered (Z)-9-hexadecenal as the key component of the Argentine ant trails. Here, we report the first chemical analyses of the trails laid by living Argentine ants and find that (Z)-9-hexadecenal is not present in a detectible quantity. Instead, two iridoids, dolichodial and iridomyrmecin, appear to be the primary chemical constituents of the trails. Laboratory choice tests confirmed that Argentine ants were attracted to artificial trails comprised of these two chemicals significantly more often than control trails. Although (Z)-9-hexadecenal was not detected in natural trails, supplementation of artificial dolichodial+iridomyrmecin trails with an extremely low concentraion of (Z)-9-hexadecenal did increase the efficacy of the trail-following behavior. In stark contrast with previous dogma, our study suggests that dolichodial and iridomyrmecin are major components of the Argentine ant trail pheromone. (Z)-9-hexadecenal may act in an additive manner with these iridoids, but it does not occur in detectable quantities in Argentine ant recruitment trails.     

A comparison of floral resource exploitation by native and invasive Argentine ants

Ants are often considered antagonists when they visit flowers because they typically steal nectar without providing pollination services. Previous research on ant–flower interactions on two species of South African Proteaceae in the Cape Floral Kingdom revealed that the invasive Argentine ant (Linepithema humile), but not native ants, displace other floral arthropod visitors. To determine how common Argentine ant use of inflorescences is, how Argentine and native ant visits differ in the numbers they recruit to inflorescences, and what factors may affect Argentine and native ant foraging in inflorescences, I surveyed 723 inflorescences in 10 species in the genera Protea and Leucospermum across 16 sites and compared ant presence and abundance in inflorescences with abundance at nearby cat food and jam baits. Argentine ants were the most commonly encountered ant of the 22 observed. Argentine ants, as well as six species of native ants were present in all inflorescences for which they were present at nearby baits. Mean Argentine ant abundance per inflorescence was 4.4 ± 0.84 (SE) ants and similar to that of Anoplolepis custodiens and Crematogaster peringueyi, but higher than observed for the other most commonly encountered native ants, Camponotus niveosetosus and Lepisiota capensis. Both Argentine ants and A. custodiens were more likely to be found foraging in spring and under humid conditions, and in inflorescences closer to the ground, with lower sucrose concentrations, and with a greater proportion of open flowers. Argentine ants were more likely to be found in Protea inflorescences, whereas A. custodiens and L. capensis more often visited Leucospermum inflorescences. Considering its displacement of floral arthropods and widespread use of Proteaceae inflorescences, the Argentine ant could be posing a serious threat to plant and pollinator conservation in this biodiversity hotspot.     

Influence of toxic bait type and starvation on worker and queen mortality in laboratory colonies of Argentine ant (Hymenoptera: Formicidae)

The efficacy of toxic baits should be judged by their ability to kill entire ant colonies, including the colony queen or queens. We studied the efficacy of four toxic baits to the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae). These baits were Xstinguish that has the toxicant fipronil, Exterm-an-Ant that contains both boric acid and sodium borate, and Advion ant gel and Advion ant bait arena that both have indoxacarb. Experimental nests contained 300 workers and 10 queen ants that were starved for either 24 or 48 h before toxic bait exposure. The efficacy of the toxic baits was strongly influenced by starvation. In no treatment with 24-h starvation did we observe 100% worker death. After 24-h starvation three of the baits did not result in any queen deaths, with only Exterm-an-Ant producing an average of 25% mortality. In contrast, 100% queen and worker mortality was observed in colonies starved for 48 h and given Xstinguish or Exterm-an-Ant. The baits Advion ant gel and Advion ant bait arena were not effective against Argentine ants in these trials, resulting in <60% mortality in all treatments. Because of the strong influence of starvation on bait uptake, control efficacy may be maximized by applying bait when ants are likely to be starved. Our results suggest queen mortality must be assessed in tests for toxic bait efficacy. Our data indicate that of these four baits, Xstinguish and Exterm-an-Ant are the best options for control of Argentine ants in New Zealand.     

Long-term field trial to control the invasive Argentine ant (Hymenoptera: Formicidae) with synthetic trail pheromone

Previous short-term experiments showed that trail following behavior of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), can be disrupted by a high concentration of synthetic trail pheromone component (Z)-9-hexadecenal. In this study, a long-term field trial was conducted in 100-m2 plots of house gardens in an urban area of Japan to see whether the control effect on Argentine ants can be obtained by permeating synthetic trail pheromone from dispensers. The dispensers were placed in the experimental plots during the ant's active season (April-November) for 2 yr with monthly renewal. To estimate Argentine ant population density, foraging activity of Argentine ants in the study plots was monitored by monthly bait surveys. Throughout the study period, Argentine ant foraging activity was suppressed in the presence of the dispensers, presumably via trail forming inhibition. In contrast, the level of foraging activity was not different between treatment and no-treatment plots when the dispensers were temporarily removed, suggesting that treatment with pheromone dispensers did not suppress Argentine ant density in the treatment plots. Population decline may be expected with larger-scale treatment that covers a significant portion of the ant colony or with improvement in the potency of the disruptant.