Comparisons between different fire ants control methods in urban environments

Many homemade methods are recommended for the control of fi re ants, but the choice of a control method for this ants in the urban environment is necessary in view of the damage they have caused to the environment and human health. Thus, the objective of this work was to compare the effi ciency of chemical (liquid insecticide and granular insecticide) and homemade (hot water and detergent water) methods used to control these ants in urban gardens. The study was conducted in the city of Juiz de Fora, MG, Brazil. The treatments were applied only once on Solenopsis saevissima colonies: (T1) Hot water, (T2) Water with detergente, (T3) Liquid insecticide and (T4) Granular inseticide. To determine the amount of applied product in T1, T2 and T3 treatments, colonies were selected by linear size and for treatment T4, colonies were classifi ed by volume. the colonies were monitored monthly for four consecutive months (July to October) to evaluate the effectiveness of the control method employed. The treatments presented distinct performances in fi re ants control in urban area, being the liquid insecticide the most effi cient in eliminating the colonies. With this study we were able to evaluate the impacts caused by each treatment, as well as the pros and cons of using each one of them, and fi nally, we suggest an effi cient fi re ants control method with lower cost per colony and less impact on the environment.


Introduction
Ants of the Solenopis Westwood, 1840 genus, better known as fi re ants, are considered one of the main invasive species in the world, standing out as pests in urban and agricultural environments where they cause serious public health issues, mainly due to accidents with humans. They are also excellent competitors, predators of invertebrates, small vertebrates and even other ant species [1][2][3][4][5]. Given the success of these ants in occupying environments altered by human activity [6][7][8], several practices have been employed for their control, such as the use of chemicals, baits and biological control [9,10].
However, when analyzing the cost, effi ciency, practicality of application and environmental impact, it is observed that there is no consensus on a method, on the contrary, the most varied recommendations for fi re ants control multiply by literature and internet.
As with most insects, fi re ants control also depends on the application of chemical insecticides [11][12][13]. Although this method temporarily reduces ants in infested regions, it does not prevent recolonization, as well as being harmful to the environment and humans, causing death or physiological and behavioral damage to non-target insects [14][15][16][17].
Another method employed is the use of toxic attractive baits, usually successful in urban áreas [20] and already reported for fi re control [10,[21][22][23]. These baits, usually granular, are carried into the nests by the ants and act at various stages of life, which can cause queen ovary retrogression, reduction in hatching rate, deformities, as well as the death of individuals [13,[24][25][26].
Homemade methods are also indicated to eliminate ants in residences and gardens. Among these methods, the use of hot water and detergent water stands out. Other options like essential oils and vinegar, which repel ants due to their strong odor; Vaseline and calcium carbonate, which create a physical barrier to ant circulation, are also reported, but these methods do not eliminate colonies, which makes their practice ineffi cient. In the United States, for example, the use of rice grains, corn and soft drinks to eliminate ants are popular, as well as other extremely environmentally dangerous products such as gasoline and diesel [27][28][29][30][31].
Thus, the objective of this work was to compare the use of chemical and homemade methods in the control of fi re ants in fi eld experiments, seeking the treatment that presents the lowest risk of contamination to the environment, lower cost per colony and the best control effi cacy.

Study area and period
The study was conducted in the city of Juiz de Fora, Minas To determine the amount of applied product in T1, T2 and T3 treatments, colonies were selected by linear size and subsequently classifi ed into small (less than 55cm), medium (56-100cm) and large (bigger than 100cm) ( Table 1). For treatment T4, colonies were classifi ed by volume (Table 1), calculated by the ellipsoid formula [6,8,32].

Discussion
In this study, Liquid Insecticide (T3) was the treatment that proved to be the most effi cient in eliminating fi re ants colonies, however, it presents high toxicity to the environment.
Liquid insecticides, widely used in urban pest management, in addition to being effective in controlling, must have mechanisms of action that prevent the selection of resistant pest populations, and also a pre-determined residual period preventing it from being exposed to the environment for a long time consequently contaminating the soil, water and neighboring animals [33,34]. In addition, due to risks during handling and product toxicity, Personal Protective Equipment (PPE) such as gloves, spray and masks are required.
Hot water is an effective method for eliminating fi re ants colonies, as the internal structure of their nests, with channels and connecting chambers, facilitate the rapid penetration of water inside, and the small size of these ants causes them to heat up and die quickly even in a brief contact with the hot water. In our study, hot water was less effi cient in the short term, but in the long term eliminated 60% of treated colonies.
Tschinkel and King JR [7], with the use of hot water, managed to eliminate 70% of fi re ants colonies in two years of study.
This methodology has also been successfully used by Tschinkel and Howard [35] and Adams and Tschinkel [36].
Handling hot water requires caution, as well as the use of personal protective equipment such as gloves and boots because at 100ºC water can cause severe burns. Water with detergent presents low risk of handling, but care should be taken that the detergent does not come into contact with mucous membranes.
In the application of granular insecticide, the risk of handling is moderate, requiring the use of gloves not to contaminate the skin.
Water with detergent is a commonly recommended method for eliminating ants in homes and gardens, being applied directly to the colony or sprayed on the ant trail [31]. Its good performance is due to easy application and handling, low cost per colony and little impact on vegetation.
Granular insecticide showed a relatively low effi cacy compared to other methods employed in this work, eliminating approximately 39% of fi re ants colonies. This low effi cacy may be related to the fact that fi re workers cannot ingest solid particles above 0.9μm. Only the 4th larval instar is able to digest solid food, and then shares it with the other colony individuals [37,38]. In addition, some authors claim that granular insecticide takes longer to make effect when in the environment, such as Aubuchon, et al. [14], who conducted fi eld and laboratory experiments with baits containing mainly Metoprene and found that the number of colonies was signifi cantly lower after 16 weeks of application, which corresponded to an effi ciency of 95% of the product. Adams, et al. [39,40] and Callcott and Collins [41], found a higher mortality of fi re ants colonies between 12 and 13 weeks after the use of baits. Fast effi ciency baits are more prone to reinfestation by fi re ants than those that provide slower initial control, and therefore generally the use of these baits requires multiple applications [42,43].
The results of this study allow us to conclude that the effi ciency of a control method is not only based on the amount of colonies that can be eliminated, other criteria such as dangerousness, risk of manipulation and impact on vegetation should also be taken into consideration because applying a product can have short-term and long-term consequences for both the environment and the locals.