Development of an effective hydrogel bait and an assessment of community-wide management targeting the invasive white-footed ant, Technomyrmex brunneus

Development of alginate hydrogel baits for the management of longlegged ant (Hymenoptera: Formicidae)

The longlegged ant, Anoplolepis gracilipes, is a globally destructive invasive species owning to its devastating impacts on biodiversity and ecosystem functions in the regions where it has been introduced. In Taiwan, invasion of A. gracilipes has been associated with the declining of land crab populations in several hotspots. While liquid baiting program has been implemented in those areas, the operation is costly and labor-intensive since it typically requires the use and maintenance of bait stations. The goal of the current study was to evaluate the potential and effectiveness of hydrogel baits laced with borax as an alternative tool to control A. gracilipes. Laboratory studies demonstrated that hydrogel baits containing 3% borax achieved higher A. gracilipes mortality than those containing 2% and 1% borax. Specifically, hydrogel baits containing 3% borax resulted in >90% worker mortality within 21 d post-treatment (LT50 = 5.1 d), along with significant reduction in brood weight (>90%) and substantial queen death (>80% of colony fragments). Furthermore, field experiment indicated that A. gracilipes workers preferentially retrieved small-size hydrogel beads (3.1 mm OD; proportion removed = 1.00 ± 0.00) compared to the larger ones (6.2 mm OD; proportion removed = 0.03 ± 0.03), which will facilitate efficient transfer of toxicant within the colony and may minimize nontarget impact. In conclusion, alginate hydrogel baits with 3% borax appear to be a promising tool against A. gracilipes, although their field efficacy against large supercolonial populations remains to be investigated.

Effect of fast and slow-acting bait toxicants on tawny crazy ant (Hymenoptera: Formicidae) foraging and nesting in the field

Tawny crazy ants (TCAs), Nylanderia fulva (Mayr) are an invasive species that develops extremely large populations that overrun landscapes. Control measures frequently rely on spraying contact insecticides, which often are inadequate. To provide insights for utilizing baits for their control, TCA foraging behavior was examined on liquid ant bait formulations that contained either fast-acting dinotefuran or slow-acting disodium octaborate tetrahydrate (DOT), and the impacts of these baits were assessed. Bayesian modeling of counts from time-lapse photography of TCA feeding on the baits and a control of sucrose solution in the field revealed strong evidence of similar foraging intensities between the control and the DOT bait and less foraging intensity on the dinotefuran bait. TCA abundance on the dinotefuran bait peaked within 8 h, then diminished to smaller feeding bouts over the 3-day study. In contrast, foraging on the DOT and control remained consistently high before bait depletion. The impact of the fast and slow-acting baits in field plots were based on TCA nest sizes and TCA abundance on sausage lures. Bayesian modeling predictions revealed nest sizes declined over the 2 months with bait present while the control had large nests. Abundance on the lures in the dinotefuran plots declined from the start of the study, while with the slow-acting DOT bait, declines in abundance were not lower than the control plot until 30 days after baiting was initiated. Further refinements in baiting with liquid baits containing fast and slow acting active ingredients may provide fast and sustained control of TCA.

Fipronil-infused sodium polyacrylate gels provide effective management of Argentine ants in conservation areas

BACKGROUND

Various types of hydrogel compounds have recently been developed for controlling invasive and pest ants in a range of environmental settings including agricultural, urban and natural areas. The current study evaluated the potential of sodium polyacrylate (ACR) hydrogels to effectively deliver liquid baits to Argentine ants.

RESULTS

Relative to standard polyacrylamide (PAM) hydrogels, individual ACR hydrogel particles were approximately five-fold heavier; this may affect how ants interact with the bait particles, and further influence bait uptake and efficacy. Additionally, ACR hydrogels had significantly higher water absorption capacity and significantly slower rate of water loss, especially during the first 2 h. The efficacy of ACR hydrogel bait containing 0.005% fipronil and various attractants was evaluated on laboratory colonies. Results demonstrated that ACR hydrogel acceptance is significantly increased by the addition of feeding attractants. In addition, a field trial was performed in a nature reserve invaded by Argentine ants to evaluate the efficacy of ACR hydrogel bait. The field trial demonstrated that ACR hydrogel bait containing 0.005% fipronil with various attractants is highly effective and that ant densities throughout the baited plots declined by >99% within 7 days.

CONCLUSIONS

The results of this study demonstrate that: (i) fipronil is highly effective for Argentine ant control in natural areas when used in low concentrations (0.005%); (ii) ACR hydrogels are an effective tool for delivering liquid baits to Argentine ants; and (iii) hydrogel baits augmented with various attractants including salt, protein and pheromone are highly attractive to Argentine ants. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Insecticide resistance in social insects: assumptions, realities, and possibilities

Insecticide resistance is an evolved ability to survive insecticide exposure. Compared with nonsocial insects, eusocial insects have lower numbers of documented cases of resistance. Eusocial insects include beneficial and pest species that can be incidentally or purposely targeted with insecticides. The central goal of this review is to explore factors that either limit resistance or the ability to detect it in eusocial insects. We surveyed the literature and found that resistance has been documented in bees, but in other pest groups such as ants and termites, the evidence is more sparse. We suggest the path forward for better understanding eusocial resistance should include more tractable experimental models, comprehensive geographic sampling, and targeted testing of the impacts of social, symbiont, genetic, and ecological factors.

Termite cuticular extracts improve acceptance of bait for controlling invasive Asian needle ants, Brachyponera chinensis

BACKGROUND

The Asian needle ant, Brachyponera chinensis, is an invasive ant currently spreading in urban and natural habitats throughout the eastern United States. Recent studies have documented the negative impact of B. chinensis on native ecosystems and human health, yet effective control strategies are lacking. Control difficulties are, in part, due to the unique biology of B. chinensis, which is a predatory ant and a termite specialist. Given that subterranean termites are an important nutritional resource for B. chinensis, the current study evaluated the potential of termite cuticular extract to improve the target-specificity and efficacy of commercial bait used for B. chinensis control.

RESULTS

The efficacy of bait augmented with termite cuticular extracts was evaluated in laboratory and field trials. In laboratory assays, B. chinensis colonies were offered granular bait treated with termite cuticular extract. Results demonstrated that the acceptance of commercial bait is significantly increased by the addition of termite cuticular extract or synthetic (Z)-9-pentacosene, a major component of termite cuticular extract. Foraging activity of Asian needle ants was significantly greater on baits augmented with termite cuticular extract or (Z)-9-pentacosene relative to standard bait. Furthermore, bait augmented with termite cuticular extract worked substantially faster relative to standard bait. To evaluate population effects, field studies were conducted in forested areas invaded by B. chinensis. Bait treated with termite cuticular extract scattered on the forest floor provided rapid control of B. chinensis and ant densities throughout the treated plots declined by 98% within 14 days.

CONCLUSION

The incorporation of termite cuticular extracts and individual cuticular hydrocarbons such as (Z)-9-pentacosene into traditional baits used for B. chinensis control may offer a novel tool to manage this increasingly problematic invasive ant. © 2023 The Author. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Exclusion of Mediterranean ant species enhances biological control of the invasive mealybug Delottococcus aberiae in citrus

BACKGROUND

Delottococcus aberiae is an invasive mealybug that produces severe damage in Spanish citrus. This mealybug has established a mutualistic relationship with native Mediterranean ant species that may limit biological control of this pest. Herein, we evaluated the effect of tending ants on the biological control of D. aberiae. To do this, we compared: (i) the density of D. aberiae, (ii) the density of its natural enemies, and (iii) the damage produced by the mealybug in trees with (control) and without ants (ants excluded with sticky barriers) in two citrus orchards across two consecutive years.

RESULTS

Lasius grandis was the most abundant ant species in both orchards and represented more than 95% of the ants tending D. aberiae in control trees. Spiders and lacewings were the most abundant predators observed in mealybug colonies, and the exclusion of mutualistic ants increased their abundance. Moreover, in control trees, ant activity throughout the year was negatively correlated with the relative abundance of predators (number of predators per mealybug). No parasitoids were recovered during field experiments. Ant exclusion reduced the density of D. aberiae and the ratio of damaged fruit at harvest across years and orchards.

CONCLUSIONS

This work corroborates the previous finding that D. aberiae benefits from its mutualistic relationship with L. grandis, probably because the presence of ants reduced the abundance of generalist predators. This mutualism can be disrupted using physical barriers on on the trunk. Further research should assess other methods of ant control that are more economic and feasible for citrus producers. © 2023 Society of Chemical Industry.

Acute toxicity of fipronil to an invasive ant, Lepisiota frauenfeldi

Slow-acting fipronil is one of the best components for controlling invasive ants. However, its efficacy against invasive Lepisiota frauenfeldi, which recently invaded Japan, remains unclear. Here, its acute toxicity to Le. frauenfeldi was assessed, and its lethal concentrations were compared with those against other invasive ants (Linepithema humile and Solenopsis invicta). The LC₁₀ and LC₅₀ values of fipronil for Le. frauenfeldi were significantly lower than the previously reported values for Li. humile and/or S. invicta, and its LC₉₀ value against Le. frauenfeldi was in the same range as that required for Li. humile extermination. Additionally, Le. frauenfeldi can be more sensitive to fipronil than non-target arthropods. Therefore, recent fipronil-based Li. humile and S. invicta eradication/control programs may be effective against Le. frauenfeldi as well. Moreover, applying fipronil at dosages appropriate for Le. frauenfeldi would lead to effective Le. frauenfeldi extermination/control with low damage to other native species/ants.