Effects of contaminants on bait acceptance by Solenopsis invicta (Hymenoptera: Formicidae)

Three commonly used fire ant baits, Amdro (0.73% hydramethylnon [AI]), Ascend (0.011% abamectins [AI]), and Maxforce (1.0% hydramethylnon [AI]), were exposed to potential, volatile contaminants. The contaminants included the insecticides Orthene Fire Ant Killer (75.0% acephate [AI] ), Cyren (44.6% chlorpyrifos [AI]), and Tempo 2 (24.3% cyfluthrin [AI]); cigarette smoke; gasoline (unleaded, 89 octane); and fertilizer (10-10-10). Fire ant baits previously exposed for 48 h to these contaminants were analyzed using gas chromatography analysis. Orthene Fire Ant Killer, Cyren, Tempo 2, cigarette smoke, and gasoline had volatile components transferred to the baits. Baits exposed to these products were used in a field evaluation of bait acceptance by Solenopisis invicta Buren, the red imported fire ant. Uncontaminated Amdro was significantly preferred by S. invicta over Amdro contaminated by smoke, Cyren, Tempo 2, and gasoline. Uncontaminated Maxforce was significantly preferred over Maxforce contaminated by Tempo 2, Cyren, and gasoline, and uncontaminated Ascend was preferred over Tempo 2- and Cyren-contaminated Ascend. Orthene-exposed Amdro, Maxforce, and Ascend baits, and smoke-exposed Maxforce and Ascend baits were not significantly different from the control. These results indicate that volatile insecticides and products can contaminate fire ant baits. Some insecticides and products, such as gasoline, can significantly affect bait palatability and may adversely impact control.     

Contamination affects the performance of insecticidal baits against German cockroaches (Dictyoptera: Blattellidae)

The effects of contamination of insecticidal bait formulations, by using mint oil and silica aerogel, were evaluated in a series of laboratory experiments against the German cockroach, Blattella germanica (L.). Bait consumption at 3 d for uncontaminated baits ranged from 0.01 g for Avert dust to 0.399 g for Combat dry bait with hydramethylnon presented in a station. LT50 values for uncontaminated gel bait deposits ranged from 0.4 d for PreEmpt containing imidacloprid to 4.1 d for Maxforce containing hydramethylnon. As a group, significantly more gel bait was consumed than solid formulations even when both formulations had similar concentrations of the same active ingredient. As a result, gel baits were significantly more toxic than solid formulations. Application of mint oil directly to bait deposits significantly decreased bait consumption and increased overall LT50 values. When bait formulation types were examined individually, there was no difference in consumption or toxicity between contaminated and uncontaminated gel formulations. Contaminated solid baits, however, had significantly greater LT50 values and less consumption than uncontaminated solid baits. Gel formulations probably absorbed the contaminants and removed them from the surface of the bait deposits resulting in normal bait consumption and toxicity. Gel and solid bait deposits, inside plastic exposure stations or alone with no station and placed onto mint oil-contaminated substrates, had significantly lower bait consumption and greater LT50 values than baits placed on uncontaminated substrates. Contamination of a baited area is more likely than contamination of just the bait deposit and therefore a more realistic test of the effects of contamination on bait performance. The importance of contamination to the performance of cockroach baits is discussed.     

Performance of gel and paste bait products for German cockroach (Dictyoptera: Blattellidae) control: laboratory and field studies.

Gel and paste bait formulations containing boric acid or hydramethylnon were evaluated in field and laboratory experiments with the German cockroach, Blattella germanica (L.). Bait formulations contained 14-62% water by weight and lost the most water after 1 d of desiccation. Bait age and water content did not alter the toxicity (LT50) of boric acid-based baits. Toxicity of hydramethylnon (Maxforce) bait, however, increased with bait age. In continuous exposure tests without harborage, boric acid formulations had LT50s of 8.5 and 10.1 d for Blue Diamond and IT WORKS, respectively. Maxforce bait had an LT50 of 4.2 d. LT50s determined with cardboard harborage or in Ebeling choice boxes were 1.5 to 2.2 times lower than those from continuous exposure tests without harborage. Relative repellency, measured as the mean percent of live cockroaches in the light side of the choice box, was greatest for IT WORKS (21.4%) and Maxforce (25.4%) formulations, followed by Blue Diamond (10.9%). A performance index that combined choice box repellency and mortality data indicated that Maxforce had the greatest potential for field effectiveness. Blue Diamond and Maxforce significantly reduced German cockroach populations in the field. Maxforce performed best in field trials when applied at 10 or 20 placements per apartment. Apartments treated with IT WORKS had significantly greater cockroach trap catches. Factors that may affect the predictive power of the performance index are discussed.     

Relative attractiveness of baits to Paratrechina longicornis (Hymenoptera: Formicidae)

Exotic ant incursions are becoming more frequent around the globe, and management with toxic baits is a suitable strategy for most species. Crazy ants, (Latreille) (Hymenoptera: Formicidae), however, are notoriously difficult to attract to commercial baits, which are generally tailored to the preferences of fire ants. We tested P. longicornis preferences for various food types and commercial ant baits. Baits trialed were commercially available products Amdro, Maxforce, Xstinguish (nontoxic monitoring version), Presto, and tuna (in spring water), sugar water (25%), boric acid (1% in 25% sugar water), and deionized water. Tuna and Xstinguish, along with sugar water and sugar water + boric acid, were the most attractive baits to P. longicornis foragers. The granular baits (Maxforce, Amdro, and Presto) were not as attractive to P. longicornis foragers. A decrease in temperature from summer (30 degrees C) to autumn (23 degrees C) trials did not seem to affect the food preferences of P. longicornis. Although P. longicornis recruitment was substantially lower during trials where there was concurrent high native ant abundance and diversity, P. longicornis still recruited to preferred baits in numbers higher than any other species. Given that tuna is impractical for management programs, the effectiveness of boric acid, sweet liquid baits in eliminating P. longicornis colonies should be compared with that of the toxic version of Xstinguish. If both are effective at eliminating colonies, we recommend sweet liquid baits containing boric acid be used for small-scale incursions (one or two nests), but a more practicable solid bait, such as Xstinguish, be used for larger scale incursions (numerous nests).     

Behavioral and physiological resistance of the German cockroach to gel baits (Blattodea: Blattellidae)

A gel bait-resistant German cockroach, Blattella germanica (L.), strain Cincy was collected in Cincinnati, OH. This strain exhibited a high level of behavioral resistance to Avert (0.05% abamectin) and Maxforce FC (0.01% fipronil) gel baits. Topical application assays indicated moderate levels of physiological resistance of the Cincy strain to abamectin and fipronil. Resistance ratios (based on LD50 values from topical applications) to abamectin and fipronil were 2.5 and 8.7, respectively. The Cincy strain of had a significantly lower LD50 value to abamectin than a nonaverse field strain (Dorie) and similar LD50 values to fipronil as the Dorie strain. The aversion behavior (avoidance of gel baits) was therefore caused by food ingredients in the gel baits. The Cincy strain showed avoidance of agar containing fructose, glucose, maltose, and sucrose, which are phagostimulants to the laboratory strain. Modifications of the inert ingredients in the Maxforce FC gel bait significantly improved the efficacy against the Cincy strain. The Cincy strain produced significantly smaller oothecae and lower numbers of eggs in each egg capsule than the nonaverse Jwax and Dorie strains of cockroaches, suggesting fitness costs are associated with resistance.     

Laboratory and field performance of an indoxacarb bait against German cockroaches (Dictyoptera: Blattellidae)

Experimental indoxacarb powder and gel baits were evaluated in the laboratory, and a gel bait was evaluated in subsequent field studies against the German cockroach, Blattella germanica (L.). In continuous exposure tests, LT50 values were 1.90 and 1.10 d for 0.25 and 1% indoxacarb powder baits, respectively. However, 0.25% indoxacarb gel bait had an LT50 value of 0.68 d, similar to a 0.05% abamectin gel bait formulated with the same bait base. There was no difference in toxicity between fresh and 7-d-old gel bait deposits. A pyrethroid-resistant strain of German cockroaches was significantly resistant to both abamectin and indoxacarb gel baits. Gel bait contained approximately 40% water, desiccated rapidly at 25-28 degrees C and 30-45% RH, but did not rehydrate when held at 56.7% RH for 3 d. Powder indoxacarb baits contained <1% water and did not desiccate or gain water. Indoxacarb gel bait (0.25%) was relatively nonrepellent (approximately 30%) and had positive maximum performance index values (approximately 100) in Ebeling choice box experiments. In field experiments in cockroach-infested kitchens, the 0.25% indoxacarb gel bait significantly reduced visual counts of German cockroaches approximately 74% at 3 d and >95% at 14 d. Indoxacarb baits are toxic, relatively nonrepellent, and can significantly reduce German cockroach populations.     

Efficacy of commercial baits and new active ingredients against firebrats and silverfish (Zygentoma: Lepismatidae)

Commercial baits containing boric acid, hydramethynon, and indoxacarb were tested against the firebrat, Thermobia domestica (Packard), and silverfish, Lepisma saccharina L. (both Zygentoma: Lepismatidae), under laboratory conditions. Three boric acid baits were consumed in significantly smaller amounts than untreated control food and did not effectively control either species. Baits containing hydramethylnon and indoxacarb were consumed in greater amounts than boric acid baits, but were relatively ineffective, with LT50 values >9 d. Presence or absence of competitive untreated food did not consistently affect bait efficacy. A ground oat matrix was used to evaluate the potential effectiveness of abamectin, chlorfenapyr, dinotefuran, fipronil, hydramethylnon, metaflumizone, and novaluron baits. The most effective compound was chlorfenapyr. At 0.05 and 0.20% (wt:wt) rates, chlorfenapyr baits produced LT50 values, for both species, ranging from 2 to 4 d. All other compounds had LT50 values >7 d.     

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.     

Genetic basis for resistance to gel baits, fipronil, and sugar-based attractants in German cockroaches (Dictyoptera: blattellidae)

A gel bait-resistant Blattella germanica (L.) strain (Cincy) was collected in Cincinnati, OH, in 2003. This strain exhibited strong behavioral resistance to Avert (0.05% abamectin), Maxforce FC (0.01% fipronil), and Pre-Empt (2.15% imidacloprid) gel baits. Reciprocal mass crosses and back crosses between the Cincy strain and a susceptible strain (Jwax) were made and tested for their inheritance of resistance to Avert, Maxforce FC, and Pre-Empt gel baits. Topical assays comparing the parental and reciprocal-heterozygous strains indicated the resistance to fipronil was incompletely recessive. LD50 and LD50 values of the Jwax male x Cincy female strain were not significantly different from he Jwax female x Cincy male strain, suggesting no sex linkage in physiological fipronil resistance. Feeding assays revealed that F1 reciprocal crosses were significantly less responsive to blank Avert and Maxforce FC baits (without active ingredients) than the susceptible strain. The Jwax female x Cincy male strain did not display significantly greater consumption of blank Avert and Maxforce FC baits relative to the Jwax male x Cincy female strain. In feeding assays with agar containing D-fructose, D-galactose, D-glucose, D-lactose, D-maltose, and D-sucrose, the crosses showed an intermediate feeding response to glucose compared with the Cincy and Jwax strains, and a similar response to other sugars compared with the Jwax strain. The Jwax male x Cincy female strain was significantly less responsive to glucose than the Jwax female x Cincy male strain. Mortality induced by Avert, Maxforce FC, and Pre-Empt gel baits against the F6 Jwax male x Cincy femaale strain was 44.2 +/- 6.8, 92.9 +/- 2.1, and 78.7 +/- 5.2%, respectively, indicating the resistance to Avert and Pre-Empt gel baits inherited by Cincy females was extremely stable. The F6 Jwax male x Cincy female strain was significantly more resistant to Avert, Maxforce FC, and Pre-Empt than the F6 Jwax female x Cincy male strain. These findings suggest that behavioral resistance to gel baits has weak sex-linkage, with a greater degree of the resistance trait being inherited by female cockroaches. Alternatively, physiological resistance to fipronil has no sex-linkage, but it is nonetheless important to the complete resistance phenotype.     

The response of German cockroaches to toxic baits:strain differences and the effects of selection pressure

Strain differences in the response of German cockroaches to toxic baits and their potential to evolve resistance to them was evaluated in choice tests. Percentage bait consumption (amount of bait consumed divided by total food consumed) was used to estimate relative attractancy/repellency of the baits. One strain apparently had low level resistance to abamectin, but no evidence of resistance was found in other strains tested with either Roach Ender or a gel bait (abamectin-based baits). Incipient behavioral resistance occurred in two strains selected for three generations with Roach Ender; a stronger response in a strain selected with the gel bait is attributed to the development of behavioral resistance. Baygon bait was highly repellent. Low level resistance to propoxur caused a large decrease in mortality compared with susceptible strains. Strong behavioral resistance developed in strains selected with Stapleton's Magnetic Roach Food.     

Attractiveness of insecticide baits for cockroach control (Dictyoptera: Blattellidae): laboratory and field studies.

Several insecticide bait formulations were evaluated for their attractiveness to cockroaches in olfactometer assays in the laboratory and in trapping experiments in the field. Included in the assays were bait stations, gels, pastes, and a powder that contained one of the following active ingredients: abamectin, boric acid, chlorpyrifos, or hydramethylnon. There were significant differences among the baits in their attractiveness to the German cockroach, Blattella germanica (L.). In trapping experiments, Avert powder (abamectin), Maxforce station and gel, and Siege gel (all hydramethylnon) were consistently attractive to B. germanica adults and nymphs. Laboratory olfactometer assays with adult males confirmed these results and showed that nymphs were as responsive as males whereas females were less responsive. Our bioassays also demonstrate that attractiveness of bait can be dramatically affected by the age of the bait. One week of aging significantly reduced the attractiveness of Avert powder in both laboratory and field assays. Aging, however did not diminish the attractiveness of Maxforce gel, indicating that the formulation may be critical for retention of attractiveness of baits. Baits that were most attractive to the German cockroach were also the most attractive to nymphs and adults of the brownbanded cockroach, Supella longipalpa (F.).     

Improving liquid bait programs for Argentine ant control: bait station density

Argentine ants, Linepithema humile (Mayr), have a positive effect on populations of mealybugs (Pseudococcus spp.) in California vineyards. Previous studies have shown reductions in both ant activity and mealybug numbers after liquid ant baits were deployed in vineyards at densities of 85-620 bait stations/ha. However, bait station densities may need to be <85 bait stations/ha before bait-based strategies for ant control are economically comparable to spray-based insecticide treatments-a condition that, if met, will encourage the commercial adoption of liquid baits for ant control. This research assessed the effectiveness of baits deployed at lower densities. Two field experiments were conducted in commercial vineyards. In experiment 1, baits were deployed at 54-225 bait stations/ha in 2005 and 2006. In experiment 2, baits were deployed at 34-205 bait stations/ha in 2006 only. In both experiments, ant activity and the density of mealybugs in grape fruit clusters at harvest time declined with increasing bait station density. In 2005 only, European fruit lecanium scale [Parthenolecanium corni (Bouché)] were also present in fruit clusters, and scale densities were negatively related to bait station density. The results indicate that the amount of ant and mealybug control achieved by an incremental increase in the number of bait stations per hectare is constant across a broad range of bait station densities. The results are discussed in the context of commercializing liquid ant baits to provide a more sustainable Argentine ant control strategy.     

Speed of efficacy and delayed toxicity characteristics of fast-acting fire ant (Hymenoptera: Formicidae) baits

Efficacy and speed of action of fire ant (Hymenoptera: Formicidae) baits that claim fast control of colonies were compared with a standard bait. More than 85% of red imported fire ant, Solenopsis invicta Buren, laboratory colonies provided bait containing the active ingredient indoxacarb died within 3 d, and all colonies were dead in 6 d. Standard bait containing hydramethylnon resulted in death of 60% of the colonies in 9 d. Bait containing spinosad did not cause colony death. Under field conditions, one-half of the areas treated with the indoxacarb bait did not have any active fire ant nests within 3 d, whereas 11 d was needed to reach the same level of control with the hydramethylnon bait. Spinosad had a maximum of 17% of the treated areas without nests after 3 d. The delay in death of S. invicta adults treated in the laboratory with the indoxacarb and spinosad baits was shorter than the standard hydramethylnon bait, which had mortality similar to the traditional delayed toxicity criterion of < 15% mortality after 24 h and > 89% mortality over the test period. Indoxacarb caused mortality of 57% at 24 h and 100% at 48 h; however, visual symptoms of toxicity were not readily observed for at least 8 h before the abrupt increase in death. Spinosad caused 96% mortality by 24 h, and initial mortality became apparent at 4 h. Time required for death of 15% of a treated population (LT15) of spinosad, indoxacarb, and hydramethylnon was 3, 9, and 16 h, respectively. Delayed toxicity characteristics of the fast-acting indoxacarb bait may be useful for the development of other fast-acting ant baits.     

Preference of food particle size among several urban ant species

Appropriate particle size may be a critical characteristic for effective granular ant baits. We examined the particle size preference of six species of pest ants to an anchovy-based bait. We also examined head capsule widths of Argentine ants, Linepithema humile (Mayr) (mean = 0.54 mm), California harvester ants, Pogonomyrmex californicus (Buckley) (mean = 1.63 mm), red imported fire ants, Solenopsis invicta Buren (mean = 0.9 mm), and southern fire ants, Solenopsis xyloni McCook (mean = 0.76 mm) and compared them with the first and second most preferred particle size. There were differences between particle size of which the most mass was removed and of which there were more particles removed by ants. California Argentine ants, southern fire ants, and Alabama Argentine ants removed more 840 to 1,000-microm particle mass of the anchovy diet but had more visits to dishes containing 420 to 590 microm particles. California harvester ants and Allegheny mound ants, Formica spp., removed more >2,000 microm particle mass but visited dishes containing 1,000 to 2,000 microm particles more often. Red imported fire ants also removed more >2,000 microm particle mass but visited dishes with 590 to 840-microm particles most often. Pharaoh ants, Monomorium pharaonis (L.), removed and visited 420 to 590-microm particles more than any other size. A linear regression model determined that particle size preferred by each ant species relates to forager head width. The majority of particles of commercial ant bait, including Amdro, Ascend, Award, Bushwhacker, Max Force with fipronil, and old and new formulations of Max Force with hydramethylnon, were 1,000 to 2,000 microm, but the majority of Niban particles were <420 microm. Altering the size of particles of toxic ant baits to fit the particle size preference of each pest ant species may increase the efficacy of ant baits.     

Toxicity of several pesticides used in Tunisia, for Aphanius fasciatus Nardo, 1827 (Pisces, Cyprinodontidae.)

The acute toxicity of some pesticides used in Tunisia is determined for the species Aphanius fasciatus (Pisces - Cyprinodontidae). Bioassays conducted at temperature (19-20 degrees C) and salinity (37-38%) have allowed to calculate the CL50 48 h and 96 h. The classification of these pesticides, based on the CL50 96 h, and according to their toxicity for the test species, shows that the organic phosphorus (Murphotox, Bazudin, Dursban, Zithiol, Lebaycid, Imidan, Oleoparathion, Folimat; Nuvan, Actellic, Carbicron, Nexion, Dimecron, Roxion) have all the degrees of toxicity, but the majority are among the most toxic; the carbamates (Betanal, Dimetilan, Baygon), are generally less toxic than the organic phosphorus tested, except Nexion which is less toxic than the Betanal and Roxion less toxic than the three carbamates tested; the herbicides (2,4-D, Basagran, Printan) have a very low toxicity, and are less toxic than the insecticides tested, except Betanal and Suffix of which the toxicity is higher than some insecticides (Nexion, Dimecron, Baygon, Dimetilan, Roxion); Calixin (Fongicide) is more toxic than the herbicides tested but it is generally less toxic than the insecticides used. At higher temperature (28-29 degrees C) A. fasciatus is more sensible to organic phosphorus (Dursban, Folimat) than to carbamate (Betanal). The variation change of salinity (from 37 to 6.5 %) don't modify the sensibility of the test species face to face of three pesticides: Dursban, Folimat (organic phosphorus insecticide) and Betanal (carbamate herbicide). A. fasciatus is suitable for acute and chronic bioassays.     

Oral vaccination against raccoon rabies: landscape heterogeneity and timing of distribution influence wildlife contact rates with the ONRAB vaccine bait

Aerial distribution of oral vaccine baits is one of the available strategies for controlling the spread of infectious wildlife diseases. This technique has commonly been used to control rabies in wild carnivores and, together with other techniques, was used to immunize wild populations of raccoons (Procyon lotor) and striped skunks (Mephitis mephitis) after the detection of the first rabid raccoon in the province of Quebec, Canada, in 2006. Vaccine bait distribution was conducted over large areas where agricultural land is dominant but interspersed with residual forest patches. Our objective was to evaluate the effect of habitat (forest vs. agricultural crops) in space and time on the contact rate between wildlife and the ONRAB(?) vaccine bait, a recent alternative to the V-RG(?). Four transects of eight vaccine baits each were installed parallel to, and at different distances from, the forest's edge (under forest cover, at field-forest edge, and at 50 and 200 m from forest edge in agricultural crops) at three sites composed of various crop types interspersed with forest patches. This experiment was conducted during three periods (late spring, 1-7 June; summer, 27 July-2 August; and fall, 24-30 October) in 2009. Contact rates with vaccine baits were monitored for 7 days in each period to evaluate the potential temporal variations generated within the habitat types. Contact rates with ONRAB vaccine baits were highest under forest cover and in the fall. Of 13 species observed in proximity to the vaccine baits, raccoons were the most frequent (49.5%, n=55 visits). Our study underlines the importance of taking into account landscape heterogeneity and timing of distribution when planning the distribution of vaccine baits to control rabies in raccoons.     

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.     

The use of alarm pheromones to enhance bait harvest by grass-cutting ants

The enhancement of bait for the control of grass-cutting ants was investigated using two species of grass-cutting ant, Atta bisphaerica (Forel) and Atta capiguara (Gon?alves) (Hymenoptera: Formicidae). Bait was applied in loose piles to obtain a direct relationship between ant attraction and bait harvest. Enhancement with alarm pheromone compounds significantly increased the attractiveness and harvest of bait under certain conditions. A large proportion of the ants attracted to the enhanced bait were minor workers. These ants rarely transport bait because of their small size, and so it may be possible to increase the effect of bait enhancement by using smaller bait granules. Foragers of A. capiguara were less inclined to transport citrus-pulp bait than were those of Atta laevigata (Fr. Smith), a species that also harvests dicotyledonous plants. This emphasizes the importance of developing a bait matrix that is more acceptable to grass-cutting species. Nevertheless, the results suggest that alarm pheromone compounds have significant potential to improve the efficacy of baits for the control of grass-cutting ants.     

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.     

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.