Host-Tree Selection by the Invasive Argentine Ant (Hymenoptera: Formicidae) in Relation to Honeydew-Producing Insects

Undesirable dispersal via a river pathway of a single Argentine ant supercolony newly invading an inland urban area of Japan

Invasive ants pose a risk to human well-being and social/ecosystem stability. Linepithema humile Mayr is among the most damaging invasive ants worldwide. Most L. humile populations invade ports/wharfs isolated from surrounding landscapes, but unfortunately, a new population was discovered in an inland urban area (Nara Prefecture) of Japan in 2021. In this study, first, the supercolony type of the Nara L. humile population was identified via a hostility test, and then its distribution pattern was characterized. In aggression tests between L. humile from Nara and four supercolonies (haplotypes LH1, LH2, LH3, LH4), this ant showed extremely strong hostility against all supercolonies exept LH2, which was detected only in Japan in its introduced range. In Nara, L. humile was abundant in and around the urban river. Simulations revealed that using this environment for movement/dispersal increased the annual dispersal ability by 14 times compared with that achieved via ground (125 m), as mentioned in the literature. Therefore, river channels can serve as major pathways of long-distance dispersal for L. humile invading inland urban areas. Since applying chemical strategies around rivers is problematic, preventing L. humile from moving to rivers from initial invasion sites is crucial.

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.

Differences in Bifenthrin and Fipronil Susceptibility Among Invasive Latrodectus spp. (Araneae: Theridiidae) and Nontarget Spiders in Japan

Prompt responses to invasive Latrodectus spiders introduced unintentionally are needed worldwide due to their medical and ecological importance. Latrodectus species are chemically controlled using pyrethroid insecticides despite concerns about the ecological impacts of these compounds on biodiversity/ecosystems. Here, the relative sensitivities (acute toxicity: 48-h LC50) of Latrodectus hasseltii Thorell and Latrodectus geometricus C.L. Koch from Japan to the conventional neurotoxic insecticide bifenthrin (pyrethroid) and a new candidate insecticide, fipronil (phenylpyrazole), were examined. Acute residual toxicity tests of these compounds in two nontarget spiders (Parasteatoda tepidariorum C.L. Koch (Araneae: Theridiidae), Badumna insignis L. Koch (Araneae: Desidae)) were conducted for comparison. To test whether bifenthrin and fipronil toxicities differed among the four spiders, corresponding species sensitivity distributions (SSDs) were compared, and hazardous concentrations were determined. Sensitivity (especially in the nontarget species) was two to four orders of magnitude higher for bifenthrin than for fipronil. The SSD patterns of the two insecticides differed significantly, with the spider communities being more sensitive to bifenthrin than to fipronil. The lethal bifenthrin concentration for Latrodectus may reduce spider populations by over 70-90%. If L. hasseltii (established throughout Japan) is targeted for effective population suppression rather than L. geometricus (with a limited distribution range) using the specified insecticide concentration (LC50 value) for fipronil, less than 20% of spider communities will be impacted. Chemical operations aimed at the effective population management and subsequent eradication of invasive Latrodectus spiders while supporting local biodiversity conservation would benefit from considerations of fipronil dosages and target species sensitivities.

Eradication and Control Strategies for Red Imported Fire Ants (Solenopsis invicta) in Taiwan

Invasive alien species are one of the major threats to biological diversity, public safety, agriculture, and economics. In recent years, a new wave of the red imported fire ant (RIFA) has been detected in new regions, including Kobe (Japan), Daegu (South Korea), Kaohsiung (Taiwan), and other locations in southeast Asia. Due to the increasing number of invasions, practitioners and scientists are seeking effective strategies to respond to RIFA invasions in Pacific regions, especially in countries that have had no presence of RIFA. This study aims to identify the strategies adopted to eradicate RIFA in Taiwan and to elucidate some of the assumptions about RIFA prevention and treatment in infested areas with diverse land patterns. Through a literature review and examination of eradication cases in Taiwan, five essential eradication lessons are discussed: (1) Immediate action through partnership with universities and the private sector; (2) engagement with the public and community with an interest in RIFA control through technology; (3) establishment of multi-level horizontal networks of response teams; (4) strategy implementation ranging from large-scale prevention to precise treatment; and (5) adoption of technology and social media. These strategies will have implications and applications for east and south Asian countries that are dealing with similar challenges.