Testing baits to control Argentine ants (Hymenoptera: Formicidae) in vineyards

Liquid baits were evaluated for control of the Argentine ant, Linepithema humile (Mayr) (Hymenoptera: Formicidae), and associated mealybug and soft scale pests in California vineyards. In 2003, liquid baits with small doses ofimidacloprid, boric acid, or thiamethoxam dissolved in 25% sucrose water resulted in lower ant and mealybug densities and fruit damage, compared with an untreated control. Similar treatments in a soft scale-infested vineyard showed only a reduction of ant density and fruit infestation in only the boric acid and thiamethoxam treatments. In 2004, commercial and noncommercial formulations of liquid baits reduced ant densities in three separate trials, but they had inconsistent effects on mealybug densities and fruit infestation; granular protein bait had no effect. Using large plots and commercial application methodologies, liquid bait deployed in June resulted in lower ant density and fruit infestation, but it had no effect on mealybug density. Across all trials, liquid bait treatments resulted in lower ant density (12 of 14 trials) and fruit damage (11 of 14 sites), presenting the first report of liquid baits applied using commercial methodologies that resulted in a reduction of ants and their associated hemipteran crop damage. For commercialization of liquid baits, we showed that any of the tested insecticides can suppress Argentine ants when properly delivered in the crop system. For imidacloprid, bait dispensers must be protected from sunlight to reduce photodegradation. Results suggest that incomplete ant suppression can suppress mealybug densities. However, after ant populations are suppressed, there may be a longer period before hemipteran populations are effectively suppressed. Therefore, liquid baits should be considered part of a multiseason program rather than a direct, in-season control of hemipteran pest populations.     

Hydrogel baits with low‐dose thiamethoxam for sustainable Argentine ant management in commercial orchards

Argentine ants, Linepithema humile (Mayr) (Hymenoptera: Formicidae), are a significant pest in various agricultural systems around the world, and are often associated with outbreaks of phloem‐feeding hemipteran insects. Previous research has evaluated a number of active ingredients and management approaches for controlling Argentine ant populations in agricultural systems, but various regulatory and economic issues have limited the development of effective management tools. Current chemical controls rely on residual sprays or toxic baits, each one posing unique disadvantages that limit their usefulness and efficacy. This study evaluated the potential of water‐storing crystals to effectively deliver liquid baits to Argentine ants. The efficacy of bait crystals containing 0.007% thiamethoxam was first evaluated in laboratory colonies. In addition, field studies were performed in a commercial plum orchard to determine the efficacy of the bait crystals. Protein marking was used within the orchard to examine the distribution of the bait in Argentine ant populations when delivered via water‐storing crystals. Results of laboratory tests showed that water‐storing crystals containing 0.007% thiamethoxam are highly attractive and effective against Argentine ants and require ca. 3–5 days to kill all castes and life stages. Results of the protein‐marking study demonstrated that the percentage of ants carrying protein‐labeled sugar water decreases sharply with increasing distance from the bait station. Bait movement was limited to within 17 m of the bait dispenser. Furthermore, bait efficacy tests in the field showed that Argentine ants can be effectively controlled using liquid thiamethoxam baits deployed via water‐storing crystals. The bait was highly effective and ant densities throughout the baited plots declined by 94 ± 2% within 14 days. The results of this study demonstrate that (1) thiamethoxam is highly effective for Argentine ant control in fruit orchards when used in low concentrations (0.007%), and (2) water‐storing crystals are an effective tool for delivering liquid baits to Argentine ants in agricultural settings.     

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.     

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.     

Impacts of Argentine ants on mealybugs and their natural enemies in California's coastal vineyards

Abstract 1. The Argentine ant, Linepithema humile, tends honeydew‐excreting homopterans and can disrupt the activity of their natural enemies. This mutualism is often cited for increases in homopteran densities; however, the ant’s impact on natural enemies may be only one of several effects of ant tending that alters insect densities. To test for the variable impacts of ants, mealybug and natural enemy densities were monitored on ant‐tended and ant‐excluded vines in two California vineyard regions. 2. Ant tending increased densities of the obscure mealybug, Pseudococcus viburni, and lowered densities of its encyrtid parasitoids Pseudaphycus flavidulus and Leptomastix epona. Differences in parasitoid recovery rates suggest that P. flavidulus was better able to forage on ant‐tended vines than L. epona. 3. Densities of a coccinellid predator, Cryptolaemus montrouzieri, were higher on ant‐tended vines, where there were more mealybugs. Together with behavioural observations, the results showed that this predator can forage in patches of ant‐tended mealybugs, and that it effectively mimics mealybugs to avoid disturbance by ants. 4. Ant tending increased densities of the grape mealybug, Pseudococcus maritimus, by increasing the number of surviving first‐instar mealybugs. Parasitoids were nearly absent from the vineyard infested with P. maritimus. Therefore, ants improved either mealybug habitat or fitness. 5. There was no difference in mealybug distribution or seasonal development patterns on ant‐tended and ant‐excluded vines, indicating that ants did not move mealybugs to better feeding locations or create a spatial refuge from natural enemies. 6. Results showed that while Argentine ants were clearly associated with increased mealybug densities, it is not a simple matter of disrupting natural enemies. Instead, ant tending includes benefits independent of the effect on natural enemies. Moreover, the effects on different natural enemy species varied, as some species thrive in the presence of ants.     

Novel bait stations for attract-and-kill of pestiferous fruit flies

A novel, visually-attractive bait station was developed in Hawaii for application of insecticidal baits against oriental fruit fly, Bactrocera dorsalis (Hendel), melon fly, Bactrocera cucurbitae (Coquillett), and Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (all Diptera: Tephritidae). The bait station developed represents a supernormal visual stimulus of papaya foliage and takes advantage of the flies' strong response to the high light-reflecting properties of yellow color and of their need for shelter, while fully protecting the bait against rainfall. Field studies revealed that the behavioral response of female fruit flies, in particular C. capitata and B. cucurbitae , to yellow-painted bait stations sprayed with GF-120 NF Naturalyte Fruit Fly Bait was significantly enhanced compared with similarly sprayed bait stations that mimicked the green color of fully grown papaya leaves. Field studies conducted with B. cucurbitae indicated that the period of bait attractiveness can be extended for at least 1 week after bait application due to the rain-fastness properties of the bait stations and the use of a visually-attractive color. Our studies provide the behavioral basis for the development of improved attract-and-kill bait stations for fruit flies in Hawaii. These devices also provide a standardized way of evaluating bait spray formulations, thus allowing for proper comparisons over time, across species, and among geographical areas.     

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.     

Hunger in red imported fire ants and their behavioral response to two liquid bait products

To help manage red imported fire ant, Solenopsis invicta Buren, invasion, several types of pest management systems have been developed, including baits. To accurately test liquid bait effectiveness in the laboratory, we determined that starvation time of 96 h is required for laboratory fire ants to simulate foraging ants in the field. We measured density and viscosity of two commercial baits and 20% sugar water at 25 degrees C and then compared amount of material consumed per ant at these physical properties. Mean densities of 20% sugar water, Dr. Moss, and Terro were 1.051, 1.287, and 1.354 g/ml, respectively, and viscosity of each bait treatment varied in the same order but more drastically (1.7, 32, and 400 centipoises, respectively). Field and laboratory studies demonstrated that bait acceptability may be affected by toxicant and physical properties. Baits that are more dense have more mass per volume and may cause the ant to cease feeding with a lower crop load than when they feed on sugar water. Ants that feed on formulated baits exhibit feeding behaviors different from those that occur when feeding on sugar water. At first glance, one might conclude that the difference is because of the toxicant, but our findings suggest that physical properties of baits may be a factor in this change in feeding behavior.     

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.     

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.     

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.     

Evaluation of non-toxic bait interference for indexing brushtail possum density

Percentage non-toxic bait interference is currently used by local authorities to monitor brushtail possum control operations but the validity of the method has not been established. Two models have been proposed to estimate an index of possum density (possums per bait) from a log-transformation of percentage bait interference. In two trials, percentage bait interference and the density index derived from percentage bait interference using the Bamford (1970) model usually increased from night to night. Variation in the number of possums per bait was reduced by dividing the Bamford index by the number of nights baits were put out, as proposed by Jane (1981). The spatial distribution of bait interference along lines of bait stations was random for the first night and usually for at least 5 nights. Rhodomine dye and cyanide poison, alternated at bait stations after at least 5 nights non-toxic baiting, showed that about 83% of possums in one trial and 29% of possums in the other trial interfered with more than one bait on the same night. Increasing the spacing between bait stations reduced the proportion of possums interfering with more than one bait. The number of possums per line killed by cyanide baits after at least 5 nights of non-toxic baiting was strongly correlated with percentage bait interference, with and without logarithmic transformation, on the first night. The possums' apparent ability to remember the location of bait stations from one night to the next means that, in the absence of better advice, the original Bamford (1970) model should be modified as proposed by Jane (1981) to estimate possum density and change in possum density (e.g., from pre- to post-poison).     

The effect of bait design on bait consumption in termites (Isoptera: Rhinotermitidae)

The efficacy of baiting as a pest control method relies on the bait appealing to the pest species. In the case of wood-eating termites, bait stations should be designed to encourage termite presence and to maximize their consumption of bait matrix in order to expedite control in minimal time. A field experiment examined the effect of bait size (one large bait or four small baits of equivalent total size, with commensurate inspection and replacement schedules), compaction (tightly rolled or loosely folded) and composition (paper only or paper plus wood) on termite presence and on untreated bait paper removal rates over four months. All three factors were significant, with bait size the most important factor, followed by compaction and then composition. The least effective baits were small, compacted (rolled) paper-only baits with monthly inspections; these had the highest abandonment rate (70%) and had the least paper removed (mean of 24 g). The most effective baits were large, folded paper-plus-wood baits with inspections at two months; these had the lowest abandonment rate (20%) and had the highest paper removal (mean of 112 g). The more than four-fold difference between these baits types demonstrates that bait efficacy can be altered considerably merely by changing bait design without adding new ingredients to the bait matrix.     

Evaluating seasonal bait delivery to badgers using rhodamine B

In the UK and Ireland, research on the control of bovine tuberculosis in badgers includes the development of a palatable bait for oral delivery of a vaccine and a means of its deployment in the field. In the present study, we carried out field deployment of bait according to the established method of bait marking in early spring and early summer to compare the effects of seasonality on bait uptake rates. All baits contained rhodamine B (RhB) which was subsequently detected in the hair and whiskers of captured badgers. During the 8 days of bait feeding at 14 badger setts, 99% of baits deployed in spring, and 100% of those deployed in summer were removed. The presence of RhB in captured badgers indicated high rates of uptake amongst adult badgers in spring (93%) and summer (98%). Only cubs captured in summer showed evidence of having taken bait (91%). Between 67% and 100% of each social group was estimated to have taken bait. The detection of RhB in 96% of badgers captured at outlier setts, where bait was not fed, suggested that deployment at main setts alone may be sufficient to target a relatively high proportion of the badger population. The number of baits deployed per marked badger suggested that a similar level of uptake might be achievable using fewer baits. The results clearly demonstrate the potential value of the bait-marking methodology for delivering vaccine baits to badgers during spring and summer, but that deployment in early summer is necessary to target cubs.     

Eradication of Norway Rats for Recovery of Seabird Habitat on Langara Island, British Columbia

Introduced Rattus norvegicus (Norway rats) caused the decline of Synthliboramphus antiquus (ancient murrelets) and other seabirds breeding on Langara Island (approximately 3,100 ha), British Columbia. Using funds from the litigation settlement following the Nestucca oil spill, Environment Canada eradicated Norway rats using a technique developed in New Zealand which involved dispensing wax baits containing the anticoagulant brodifacoum at 50 ppm from fixed bait stations. Bait stations were placed every 75 to 100 m on a grid over the entire island (1 station/ha). Rats removed bait for 26 days, after which crews placed baits in protective plastic bags in each bait station. Stations loaded with baits were left on the island and rechecked four times over 2 years, after which bait stations and remaining bait were removed. The eradication succeeded. No signs of rats have been detected on Langara Island and its associated islands since January 1996. No rats were trapped during 1,700 trap‐nights following the poison campaign. Incisor marks of rats were not found on apples or oil‐dipped chew‐sticks. Corvus corax (common ravens) likely suffered greater than 50% mortality from the eradication after apparently gaining access to the poison directly from bait stations and from scavenging rat carcasses. A monitoring and response system is being developed in conjunction with current users of the islands. The success on Langara Island demonstrates how the technique proven on small New Zealand islands of less than 300 ha can be effectively extrapolated to much larger islands.     

Detrimental effects of highly efficient interference competition: invasive Argentine ants outcompete native ants at toxic baits

The Argentine ant (Linepithema humile) is an invasive species that disrupts the balance of natural ecosystems by displacing indigenous ant species throughout its introduced range. Previous studies that examined the mechanisms by which Argentine ants attain ecological dominance showed that superior interference and exploitation competition are key to the successful displacement of native ant species. The objective of this research was to test the hypothesis that effective interference competition by Argentine ants may also be detrimental to the survival of Argentine ant colonies where Argentine ants and native ants compete at toxic baits used to slow the spread of Argentine ants. To study this hypothesis, we examined the competitive interactions between Argentine ants and native odorous house ants, Tapinoma sessile, in the presence and absence of toxic baits. Results showed that Argentine ants aggressively outcompete T. sessile from toxic baits through efficient interference competition and monopolize bait resources. This has severe negative consequences for the survival of Argentine ants as colonies succumb to the toxic effects of the bait. In turn, T. sessile avoid areas occupied by Argentine ants, give up baits, and consequently suffer minimal mortality. Our results provide experimental evidence that highly efficient interference competition may have negative consequences for Argentine ants in areas where toxic baits are used and may provide a basis for designing innovative management programs for Argentine ants. Such programs would have the double benefit of selectively eliminating the invasive species while simultaneously protecting native ants from the toxic effects of 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.     

Carbohydrate supply limits invasion of natural communities by Argentine ants

The ability of species to invade new habitats is often limited by various biotic and physical factors or interactions between the two. Invasive ants, frequently associated with human activities, flourish in disturbed urban and agricultural environments. However, their ability to invade and establish in natural habitats is more variable. This is particularly so for the invasive Argentine ant (Linepithema humile). While biotic resistance and low soil moisture limits their invasion of natural habitats in some instances, the effect of food availability has been poorly explored. We conducted field experiments to determine if resource availability limits the spread and persistence of Argentine ants in remnant natural forest in North Carolina. Replicated transects paired with and without sucrose solution feeding stations were run from invaded urban edges into forest remnants and compared over time using baits and direct counts at feeding stations. Repeated under different timing regimes in 2006 and 2007, access to sucrose increased local Argentine ant abundances (1.6–2.5 fold) and facilitated their progression into the forest up to 73 ± 21% of 50-m transects. Resource removal caused an expected decrease in Argentine ant densities in 2006, in conjunction with their retreat to the urban/forest boundary. However, in 2007, Argentine ant numbers unexpectedly continued to increase in the absence of sugar stations, possibly through access to alternative resources or conditions not available the previous year such as honeydew-excreting Hemiptera. Our results showed that supplementing carbohydrate supply facilitates invasion of natural habitat by Argentine ants. This is particularly evident where Argentine ants continued to thrive following sugar station removal.     

Efficacy of broadcast and perimeter applications of S-methoprene bait on the red imported fire ant in grazed pastures

The red imported fire ant, Solenopsis invicta (Buren), is a major pest in the United States because of its painful sting. Toxic bait has been an important management tool against fire ants, but site registrations prohibit applications of most baits on grazed pastures. Extinguish, containing the insect growth regulator methoprene, was selected for this study because it has a broad site registration that includes grazed pastures. The primary objective of this research was to evaluate the efficacy for control of red imported fire ants by using broadcast applications of methoprene bait at a label rate of 1,121 g/ha versus applications around the perimeter of a target area at the reduced rate of 280 g/ha. Grazed pastures in Lee County, Alabama, and Chambers County, Alabama, were selected for this study, with broadcast treatments, perimeter treatments, and controls replicated three times at each site. All mounds were counted and rated using the USDA population index before applications and then at 8 and 16 wk posttreatment. Perimeter applications did not significantly reduce S. invicta mound abundance, but bait treatments significantly reduced mound abundance at 16 wk posttreatment at site 1 where applications were conducted in early evening. However, broadcast applications were not effective at site 2 where treatments were conducted in early morning with warmer temperatures. Emergence of winged alates was observed at 12 wk posttreatment, followed by a high density of incipient mounds that may have masked the full treatment effect of methoprene applications at site 2. Methoprene bait was effective in reducing abundance of S. invicta only when full label rates were applied.     

Efficacy of wax matrix bait stations for Mediterranean fruit flies (Diptera: Tephritidae)

Tests were conducted that evaluated efficacy of wax matrix bait stations for Ceratitis capitata (Wiedemann) adults in Guatemala. Bait stations were exposed to outdoor conditions to determine effect of weathering on longevity as indicated by bait station age. Results of laboratory tests found that bait stations with spinosad and ammonium acetate remained effective for at least 31 d compared with pesticide-free controls, although there was some loss of efficacy over time. Percentage mortality for bait station strips with 2% spinosad and 1% ammonium acetate decreased from 100 +/- 0.0% on day 0 to 70 +/- 7.1% after 31 d. Ammonia concentration had little effect on percentage mortality although there was some indication that ammonia concentration affected number of flies observed on the bait stations. Bait station strips (one per cage) were more effective than controls for 6-8 wk when tests were conducted in field cages (3 m diameter x 2 m), but only 2-3 wk when tests were conducted in large (2.5 m high and 6.0 m wide and 7.5 m long) field cages. Longevity was restored when multiple bait stations (3, 6, or 12) were deployed per cage. Bait stations containing methomyl were used for field tests of efficacy for wild flies. Dipped lure bait stations, which were made by coating two edges of commercial ammonium acetate and trimethylamine lures, killed six times more flies than corn cob bait stations dipped into a Nulure/malathion solution. They also killed more flies than pesticide-free controls for 8 wk.