Combined effect of hemipteran control and liquid bait on Argentine ant populations

The invasive Argentine ant, Linepithema humile (Mayr), has become a worldwide problem capable of inflicting significant ecological and economic injury on urban, agricultural, and natural environments. The mobility of this pest ant has long been noted, rapidly moving nests to new food resources and then away as resources are depleted. This ant, like many pest ant species, has a special affinity for honeydew excreted by phloem-feeding Hemiptera. We investigated the effect of various hemipteran control strategies on terrapin scale densities and measured their indirect effect on local Argentine ant densities and foraging effort. We then determined whether this indirect treatment strategy improved the performance of an ant bait. We predicted that Argentine ants would move nests away from trees treated for Hemiptera and then move nests back when a liquid bait was offered, followed by a decline in ant numbers due to intake of the toxicant. A horticultural oil spray and soil application of the systemic insecticide, imidacloprid, had no effect on terrapin scale numbers. However, trunk-injected dicrotophos caused a reduction in scale and a decline in local Argentine ant nest density and canopy foraging effort. We also recorded a reduction in local Argentine ant ground foraging when large amounts of liquid bait were applied, and we found no evidence that combining dicrotophos with liquid ant bait performed better than each treatment alone. We suggest that a strategy of combined hemipteran control plus application of liquid ant bait can reduce local Argentine ant densities, when both components of this system are highly efficacious.     

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.     

Strategies for controlling the ghost ant,Tapinoma melanocephalum (Hymenoptera: Formicidae) with liquid bait

The ghost ant, Tapinoma melanocephalum (F.), is a household pest and a considerable nuisance. The aim of this study is to demonstrate the toxicity and control efficacy of boric acid in liquid bait against queen and worker ghost ants. The LT₅₀ values for workers fed with 0.5%–2.5% boric acid and 2% chicken peptone in 20% sucrose water solutions were 4.3–2.4 days. The lethal times (LT₅₀ = 5.2–7.6 days) for queen ghost ants fed with various concentrations of a boric acid solution depended on the feeding behavior of the queens. The high boric acid (4%) content solutions were not repellent to the ghost ant workers. The liquid bait formulation of 1% boric acid, which caused a 100% worker, brood, and queen population reduction in 4, 4, and 5 weeks, respectively, was significantly more effective than the solid bait formulation containing the same concentration (p ≦ 0.05). The simulation tests involved using chicken peptone and sucrose as the attractant, and colonies were provided an alternate food source (20% sucrose solution and dog food) to achieve a more accurate assessment of bait acceptability in screening for the efficacy of the liquid boric acid bait. The control efficiency attained 99.9% in week 4. The results demonstrated that liquid bait, containing 2% chicken peptone, 20% sucrose as a food attractant, and 1% boric acid as the toxin, is efficient and highly recommended for ghost ant control.     

Argentine ant (Hymenoptera: Formicidae) trail pheromone enhances consumption of liquid sucrose solution

We investigated whether the Argentine ant, Linepithema humile (Mayr), trail pheromone, Z9-16:Ald, could enhance recruitment to and consumption of liquid sucrose solutions. All tests were done as paired comparisons with a 10% sucrose solution as food. In the laboratory, mixing 20 microl of a 10-microg/ml solution of the pheromone with 50 microl of the 10% sucrose solution increased the number of ants feeding by >150%. In a field test, we combined the trail pheromone with a 10% sucrose solution in 50-ml vials. These vials were covered with a plastic membrane that has 1.5-mm-diameter holes punched uniformly across its surface. Ants could drink from the holes after the vials were inverted. For half of the vials, 1 microg of the pheromone was put onto the plastic membrane before the vials were filled with a 10% sucrose solution. The remaining vials had no pheromone on the plastic membrane. After 4 h we measured the consumption in each vial. Bait consumption with the pheromone was enhanced by 29%. In a 2nd series of tests, vials were left outside for 24 h. The consumption rate was 33% higher with the pheromone compared with the controls that didn't have pheromone.     

Protocols for Argentine ant eradication in conservation areas

The Argentine ant (Linepithema humile) is a widespread, abundant and ecologically disruptive invader that is present throughout major portions of coastal California and on half of the California Channel Islands. On Santa Cruz Island, the Argentine ant had invaded about 2% of the island's area in four distinct locations as of 2012. Given the negative ecological effects resulting from Argentine ant invasions, we sought to develop a cost‐effective method of eradication. Here, we describe the results of large‐scale, field‐tested methods for Argentine ant eradication and post‐treatment detection. Our eradication protocol employs a novel toxicant‐delivery system: an aqueous solution of sucrose and 6 ppm of thiamethoxam mixed with hydrating polyacrylamide beads. Ants feed on the solution present on the bead's surface for about 24 h after which time bead dehydration prevents feeding. We distributed hydrated beads by helicopter over 74 ha of infested areas plus a 50‐m buffer on 14 occasions between June 2013 and September 2014. Treatments reduced Argentine ant activity to subdetectable levels within four months. In 2014, we conducted a high‐intensity detection protocol using lures (n = 55 363) in areas treated in 2013. This effort did not detect Argentine ants. In 2015, we conducted a medium‐intensity detection protocol using lures (n = 2250) in areas treated in 2013 and 2014 but not searched in 2014; this sampling effort did not detect Argentine ant activity except for a single remnant infestation (c. 0.3 ha in area), which was retreated in 2015. The cost of treatments was approximately $1400 per ha; this cost is comparable to other ant eradication efforts. The cost of our preferred detection method, which used lures spaced every 10 m, was $500 per ha. These results demonstrate sufficient protocol efficacy to justify expansion of treatments to other infested areas in ecologically sensitive areas.     

Gyne development in the Argentine ant Iridomyrmex humilis: role of overwintering and queen control

Abstract A possible stimulatory effect of overwintering on gyne development in Iridomyrmex humilis (Mayr) was investigated. Although gyne-potent larvae are present in the nest throughout the year, small queenless colony fragments composed of freshly overwintered ants (collected in late winter or early spring) produced 3–8 times more gynes than comparable fragments made up of non-freshly overwintered ants (collected at other times of the year). Apparently, this stimulatory effect of overwintering acts on both the developmental potential of larvae and the tendency of workers to rear sexually competent larvae as gynes; queenless colony fragments in which either the brood or workers were freshly overwintered produced more gynes than fragments composed of non-freshly overwintered workers or brood but fewer than fragments containing both brood and workers freshly overwintered. This increased sexualization potential of larvae due to overwintering is enough to overcome weak pheromonal inhibition of queens associated with low queen number; a single queen in a large freshly overwintered colony fragment is insufficient to inhibit gyne development, whereas ten queens are totally inhibitory. In non-freshly overwintered colony fragments one queen is completely inhibitory. Variability in egg developmental potential according to queen age does not appear to play a major role in the seasonal production of gynes, because at least some eggs of very young queens (less than 3 weeks old) are capable of gyne development. In the field this stimulatory effect of overwintering is superimposed on a seasonal fluctuation in the combined strength of pheromonal queen control. In southern France, gynes are produced only in spring where they arise primarily from overwintered larvae just after a sharp drop in queen number, and presumably the total level of inhibitory queen pheromone, due to the massive execution of queens by workers.     

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.     

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.     

Acceptance and intake of gel and liquid sucrose compositions by the Argentine ant (Hymenoptera: Formicidae)

Liquids and gels are common delivery forms used in commercial ant baits, but the relative effectiveness of each is unknown. We compared the feeding responses of the Argentine ant, Linepithema humile (Mayr), to liquid and gel compositions of sucrose. In choice assays, more workers were counted on gel than liquid; however, substantially more liquid was consumed. Because workers could stand on the gel, more workers could feed simultaneously on the gel. The feeding bouts of individual workers, however, were much less efficient at extracting sucrose in gel form. Workers fed eightfold longer on the gel, yet removed fivefold less sucrose than workers feeding on liquid. This potential bias should be considered during attraction and palatability studies that use physically different bait compositions. When the toxicant fipronil was added to the compositions, a greater proportion of the colony died after workers had fed on liquid than gel baits. This finding suggests that liquid formulations may provide more effective control of Argentine ants due to the greater speed and abundance in which it is ingested.     

The spread of the Argentine ant: environmental determinants and impacts on native ant communities

The increasing numbers of invasive species have stimulated the study of the underlying causes promoting the establishment and spread of exotic species. We tracked the spread of the highly invasive Argentine ant (Linepithema humile) along an environmental and habitat gradient on the northeastern Iberian Peninsula to determine the role of climatic, habitat and biotic variables on the rate of spread, and examine impact on native ant communities. We found the species well-established within natural environments. The mean annual rate of spread of the invasion (7.94 ± 2.99 m/year) was relatively low compared to other studies, suggesting that resistance posed by native ants in natural environments with no or low human disturbance might delay (although not prevent) the spread of the invasion irrespectively of the land-use type. Factors related to the distance to urban areas and characteristics of native and introduced populations explained the rate of spread of the invasion, while habitat-related variables determined the distribution of native ants and the impact of the Argentine ant on them. Native ant communities became more homogeneous following the invasion due to the decline of species richness and abundance. Only few species (Plagiolepis pygmaea and Temnothorax spp.) were able to cope with the spread of the invasion, and were possibly favored by the local extinction of other ant species. Taken together, our results indicate that land uses per se do not directly affect the spread of L. humile, but influence its invasive success by molding the configuration of native ant communities and the abiotic suitability of the site.     

Scavenging in Mediterranean ecosystems: effect of the invasive Argentine ant

Above-ground invertebrates may represent a high proportion of animal biomass, but few data are available on their fate after death. In Mediterranean ant communities, they are frequently scavenged by ants. Here, we assessed the consequences of Argentine ant invasion on the removal of arthropod corpses in Doñana National Park (SW Spain). In three natural habitats that differed in their degree of vegetation cover (i.e. protection for ants against high temperatures), we experimentally provided dead Drosophila, and observed their disappearance over a 60-min period at different times of day and year. The habitats used were isolated cork oak trees, pine tree forest and dry scrubland; we compared invaded with uninvaded plots in each. Oak trees were the most invaded habitat, while scrubland was the least and the only one where the Argentine ant coexisted with native ant species. In accordance with this degree of invasion, the Argentine ant removed the highest percentage of dead flies in oak trees and the lowest in scrubland. Its performance as scavenger was higher than uninvaded ant communities, but it was reduced at high temperatures, when native species were highly efficient. The saturated distribution of the Argentine ant colony seems to be the key to its efficiency. We discuss how the occurrence and scavenger efficiency of the Argentine ant could affect the nutrient cycling and the progression of its invasion.     

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.     

Genetics and behavior of a colonizing species: the invasive Argentine ant

Baker and Stebbins's 1965 book The Genetics of Colonizing Species aimed to draw together scientists from a variety of disciplines to provide a conceptual framework for the study of species introductions. A goal of their volume was to examine how studies on biological invasions could be used to provide insight into basic research questions as well as to develop practical strategies for control. In this article, we attempt to follow the goals of Baker and Stebbins by reviewing work on the genetics and behavior of a widespread colonizing species, the Argentine ant (Linepithema humile). Specifically, we examine the evolutionary changes that have taken place as a result of this species being introduced into new environments and synthesize recent research on Argentine ants from the perspective of population genetics, recognition systems, and the mechanisms that may underlie their ecological success.     

Nest site selection by the Argentine ant and suitability of artificial nests as a control tool

The Argentine ant is an invasive species that has been introduced worldwide causing devastating effects on entire ecosystems. Control strategies might be focused on slowing its rate of spread to limit its establishment inside yet non-invaded areas. For this, a better knowledge about nest selection is necessary to identify rapidly and accurately nest locations where to apply control measures. Herein, nest site selection by the Argentine ant, nests’ physical characteristics and their longevity were studied in three invaded cork oak secondary forest. Results showed that this species shifts nest locations seasonally to keep appropriate microclimatic conditions, nesting mainly underneath rocks during cold and rainy months and in tree bases during warmer periods. The terrain features at micro-scale (orientation and slope) were found to influence the distribution of the Argentine ant nests beneath rocks. Additionally, artificial nests used as a control tool were tested, finding that their use may be suitable if they are set in appropriate locations and before the ants start migrating to winter aggregations.     

红火蚁克星对入侵红火蚁的防治效果

经过一年来的野外试验,结果表明红火蚁克星对红火蚁具有显著的控制效果.施药后4d,红火蚁全巢死亡率达83.33～92.31%,施药后7～10 d全巢死亡.施药后90d和180d监测结果表明,诱测点在6个月内未出现新的蚁巢.     

Red imported fire ant (Hymenoptera: Formicidae) control with a corn grit bait of fenoxycarb without soybean oil

The standard fenoxycarb fire ant bait formulation (Logic), composed of pregel defatted corn grits and soybean oil toxicant, was modified by eliminating the soybean oil. This formulation without soybean oil contained greater than 2 times more fenoxycarb and was as effective as the standard bait formulation against laboratory colonies of red imported fire ant, Solenopsis invicta Buren. In field tests, the modified and standard baits were equally effective in controlling fire ants after 6, 12, and 18 wk. Individual worker ants obtained from plots treated with fenoxycarb baits without soybean oil had greater than 47 times less fenoxycarb than did workers from the plots treated with the standard fenoxycarb baits containing soybean oil.