2. Examples of Argentine Ant Control Internationally Fig. 1 The Argentine ant Linepithema humile (photo by Yoshiko Sakamoto). K. GOKA 1936), they have continued to expand their distribution. Currently, they are widely distributed not only in California but also across the southern United States, including Georgia, South Carolina, Alabama, Mississippi, Louisiana, Florida, Tennessee and North Carolina (Angulo et al., 2024). They are also found in the mountainous areas of Maui in the Hawaiian Islands (Angulo et al., 2024). In the United States, numerous studies have been conducted on chemical control methods for Argentine ants (Rust et al., 2003; Klotz et al., 2009; Choe et al., 2021); but so far, these efforts do not appear to have been effective in suppressing the spread of Argentine ants within the country. In 2010, when I personally went to survey an infested area on the outskirts of San Diego, I witnessed endless trails of Argentine ants spread across a vast grassland with no visible boundaries, and I realized the situation was beyond control. One successful control case in US was a project on Santa Cruz Island off the coast of California, where a population of Argentine ants was nearly eradicated through a year-long bait treatment program. In this control project, from June 2013 to September 2014, a total of 14 applications of gel-bead baits containing a neonicotinoid insecticide, thiamethoxam, were applied by helicopter over a 74-hectare infested area and a 50-meter buffer zone surrounding it. As a result of this bait treatment, the Argentine ants decreased to undetectable levels within four months, and by 2015, it was shown that the Argentine ant had been eradicated in almost all areas of the island, except for a residual area of approximately 0.3 hectares. The control costs at that time were estimated to be approximately $1,400 (about 200,000 yen) per hectare, resulting in a total budget of approximately 15 million yen for the entire island (Boser et al., 2017). Another successful case was the treatment of San Clemente Island, California. Applied by hand, helicopter and ATV, hygroscopic polyacrylamide beads were used as a bait matrix to deliver a liquid bait (thiamethoxam and sucrose) to Argentine ant infestations at five sites (totaling 177 ha) on San Clemente Island. The treatment reduced the number of monitoring points at which the Argentine ant was detected one year posttreatment (17.91% vs. 3.65%) (Merrill et al., 2018). 2.2 Control of Argentine Ants in Australia The first established population of this species was identified in Melbourne in 1939 (and maybe as early as 1931) (Pasfield, 1968; Wetterer et al., 2009). Since then, it has spread in southern Australia (Suhr et al., 2009). In 2009, an established population was also confirmed in Queensland (Suhr et al., 2009). In each state of Australia, laws regarding Argentine ants have been enforced, and control measures are being implemented (e.g., NSW Government, undated). According to a report by Hoffman et al. (2011), the larvae with Originally, not only invasive ants but also various other ant species have been targeted for control as nuisance pests, leading to the development of various chemical agents. A variety of insecticidal compounds and formulations are used in ant control agents (Picanço et al., 2023). As they are social insects, in the control of ants the primary targets of chemicals are the queen and larvae of new queens, which are the reproductive units of ant colonies. No matter how many worker ants outside the nest are exterminated, as long as the queen and larvae inside the nest remain alive, the worker ants will be replenished, and if new queens mature, the number of nests will continue to increase. It is difficult, however, to apply chemicals directly to queen ants or larvae living deep inside complex nests. Additionally, invasive ants such as Argentine ants have highly mobile queens (Hertzer, 1930; Newell & Barber, 1913; Harris, 2002), and if the nest environment is disturbed by the application of sprays or liquid chemicals, there is a risk that the queen ants may escape or disperse. Therefore, in controlling ant nests, a reasonable formulation for is considered to be bait containing insecticides among the food ingredients. To ensure that worker ants reliably feed the bait, slow-acting the queen and insecticides such as neonicotinoids or phenylpyrazoles, or insect growth regulators (IGRs) are considered more suitable than fast-acting insecticides like pyrethroids (Goka & Sakamoto, 2019). Chemical control measures have been implemented worldwide against invasive populations of Argentine ants. Below are examples of control cases with specific data. Since established populations of Argentine ants were first discovered in Ontario, California, in 1905 (Smith, insecticides throughout temperate areas 118 require time. 2.1 Argentine Ant Control Cases in the United States
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