E. SUNAMURA et al. virtually no pest management professionals on the island, the concept of these hydrogel baits was “easily formulated and treated using easily available materials.” For example, the superabsorbent polymer was chosen from acrylic acid polymers readily available from online stores. The formulated hydrogel baits induced higher T. brunneus recruitment than peanut cream and 10–30% sugar water, 10% honey water, and tap water soaked into cotton pads (Sunamura et al., 2022). 5.4 Community-wide Management Program involving Citizens on Hachijo Island To solve serious problems of T. brunneus in residential areas, the government of Hachijo Island launched a management program in 2020 (Terayama et al., 2021a). The authors have been involved in the program as external advisors. A community-wide hydrogel bait treatment was conducted in May 2021, targeting Kashitate Village. Approximately 500 kg of the aforementioned hydrogel baits were prepared by the local government staff and residents (Fig. 3). The baits were divided into plastic containers (1.8 kg) and delivered to 272 residences, 18 public facilities and two shrines. The residents were instructed to deploy the baits around their houses on the designated date (May 30). The population density of T. brunneus declined to 13% of its pre-treatment level at nine days after treatment (Sunamura et al., 2022). Additionally, a follow-up survey demonstrated that the residents regarded the hydrogel baits as easy to apply, attractive to T. brunneus and very effective. The T. brunneus density, however, recovered to 68% of its pre-treatment state at 37 days after treatment. In the tested village, residences were sparsely distributed and surrounded by forests or shrubs. Thus, the quick recovery of T. brunneus was likely due to re-infestation from intact as surrounding nests aforementioned. Additionally, the weak horizontal transfer of insecticides among nests might have been a reason for the relatively short control efficacy. in A survey on Hachijo Island suggested that this treatment reduced T. brunneus intrusion into houses Insecticidal baits are the most realistic and effective tool for controlling invasive ants over relatively large areas of infestation, because broadcast spraying of insecticidal liquids is cost-prohibitive and not eco-friendly (Hoffman et al., 2016). Commercial ant baits available in Japan, however, are not suitable for practical use against T. brunneus. We previously investigated the attractiveness of various commercial ant baits to T. brunneus and found that granular, paste and gel baits available in Japan are not attractive to T. brunneus (Terayama et al., 2021b). In contrast, sugar water and a sugar-based liquid bait were attractive. This may reflect the fact that the main diet of T. the brunneus honeydew provided by hemipteran insects and plant nectar (Fig. 1). is carbohydrate-rich Similarly, T. difficilis notably prefers carbohydrates to proteins or lipids (Klotz et al., 2008). Warner and Scheffrahn (2004, 2005) found that sugar-based liquid baits are promising for controlling T. difficilis and the optimal sucrose concentrations to induce T. brunneus recruitment are 25%–40%. Additionally, recruitment of T. difficilis can differ among different saccharides (Warner, 2003; Kafle et al., 2020). The above information suggests that sucrose-based liquid baits are most suitable for recruiting T. brunneus. However, liquid baits are readily absorbed into the soil and lost when sprayed directly on the ground and thus require bait stations. Deployment of numerous bait stations over a large area, however, is cost-prohibitive and labor-intensive. Additionally, the bait stations become litter after use and are harmful to the environment unless retrieved. Hydrogel baits are polymers. insecticides, To control T. brunneus on Hachijo Island, hydrogel baits containing 10 ppm thiamethoxam as the insecticide and 20%–30% sugar as the feeding stimulant were developed (Sunamura et al., 2022). Because there are liquids such as liquid baits sustained by contains liquid superabsorbent water-soluble stimulants and sometimes attractants. Because the amount of solid constituents (polymers) is very small, hydrogel baits are water-rich. Therefore, hydrogel baits have been increasingly used for controlling liquid-feeding ant species such as L. humile in recent years (Buczkowski et al., 2014; Tay et al., 2020). When hydrogel baits are sprayed directly on the ground, the superabsorbent polymers sustain the liquid content and prevent it from being absorbed into the soil. Thus, hydrogel baits can overcome the aforementioned deployment issue of liquid baits and reduce the costs associated with manufacturing and retrieving bait stations. These characteristics make hydrogel baits highly and easy-to-handle baits for liquid-feeding ants. The feeding acceptable, low-cost Therefore, regular hydrogel bait preparation and treatment were initiated in Hachijo Island’s T. brunneus management program. Because hydrogel baits can be prepared easily at a low cost, effective management is feasible by the residents themselves within the budget of their local government. The program was conducted in one village in 2021 and was expanded to three villages in 2022 and then all five of the villages of Hachijo Island in 2023. Further, a biodegradable microfibrillated cellulose hydrogel bait was newly developed and commercialized (Terayama et al., 2024). This product replaced the and self-manufactured hydrogel bait significantly reduced the labor for the local government associated with regularly preparing hydrogel baits. such environments, from 2024 138 5.2 Bait Preference Biased to Liquids 5.3 Development of Hydrogel Baits
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