145 Fig. 3 The percentage significant Fig. 4 Hot vapor is ejected using an injector device. Fig 5. This diagram shows suggested lethal temperatures (orange color) of hot water vapor steaming in a RIFA nest (brown color). of nests active difference between the liquid-nitrogen-treated group dropped to 10% in the 14th day following the treatment. The asterisks indicate a the statistically liquid-nitrogen-treated nests and the controls. (Modified from Lin et al., 2013.) in Fig. 6 Dry ice is poured into an opened mound, forming Fig. 7 The treated mound is closed and sealed tightly after water fog around the mound. being filled with dry ice. Technologies for fire ants control queens and juvenile individuals, including eggs, larvae and pupae (unpublished data). Small dry ice pellets (3 x 5 mm) are placed on the mound surface first to calm and paralyze the ants. Then the mound top is opened to create a cavity and dry ice pellets are poured into it (Fig. 6). Finally, the cavity is filled with soil and covered tightly with plastic sheeting to prevent the CO2 from venting rapidly, keeping as much of the CO2 gas as possible in the nest. (Fig. 7) (APHIA, 2023) Dry ice absorbs nearby heat and volatilizes into CO2 at temperatures above −78.5°C. When treating RIFA nests, the released CO2 paralyzes and immobilizes RIFA. Because it is heavier than air, it stays mostly in the spaces of the nest and continuously stuns RIFA. The temperature of RIFA and the surrounding environment is also reduced rapidly, eventually killing RIFA. Dry ice treatment also prevents alates, especially queens, from escaping, minimizing the risk of the colony spreading, and resulting in high mortality. The methods mentioned above confer massive killing of RIFA and fewer residual effects, and they are odorless and friendly to the ecosystem. The costs of hot water vapor steaming, dry ice treatment and liquid nitrogen freezing are estimated at about US$1, $2, $9, respectively, Both liquid nitrogen freezing and hot water vapor steaming eliminate most of the creatures around the zone treated, but some insects or animals were observed in the hours following, and plants were also seen emerging days after the treatment. Although insecticide treatment incurs the lowest costs, it bears a relatively high impact on the environment, and seems prone to RIFA reinvasion (unpublished data). For areas where conventional insecticides or heavy equipment are not suitable to use, like in urban areas, or organic farms, granular dry ice could also be applied to eliminate the entire RIFA nest. Dry ice treatment kills all classes of ants in the nest, including worker ants, alates,
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