Introduction of chemical control

The key to a fire ant colony is the queen. Therefore, any control method which does not effectively control the fire ant queen can be considered only a temporary solution to the problem. The US Department of Agriculture (USDA) conducted a large-scale control and eradication program against the RIFA by spraying pesticides. Based on the nature of their biology, queens live in the inner part of mounds with heavy protection; therefore, even though fire ants on the soil surface may die immediately after chemical spraying, new members are rapidly created by reproductive queens. Therefore, to effectively control the fire ant, a two-step control method was used in the US.

Step 1. Bait treatment: Bait is broadcast around a mound, and foragers carry the bait into the mound to feed the queen.

Step 2 Individual mound treatments: Chemicals, such as a contact insecticide, or non-chemical methods, such as boiling water or detergent, are applied to eliminate the workers and males, and even queens of mounds.

After many modifications developed in the US and Australia, the method of bait treatment in step one and contact insecticide in step two is considered the best method for controlling fire ants.

Step one: Bait treatment

Most fire ant bait is made from an insecticide and a lure (generally processed corn grits coated with soybean oil). Soybean oil is a critical component of bait that effectively attracts foragers. However, the quality of soybean oil degrades fast and its power of attraction decreases, so it is recommended that fresh bait be regularly broadcast. Two major types of chemicals known as insect growth regulators (IGRs) and toxicants are usually used with the application of bait.

Many studies have suggested that regardless of the type of bait used, the control rate appears to be very similar (85%~95%). However, the 2 types pose major differences in the length of time it takes to cause a reduction in population size. Generally speaking, IGRs work more slowly but are persistent for a longer period so that they effectively control the expansion of ants.

Forager ants carry the bait inside the mound and feed the entire colony including reproductive queens by the process of trophallaxis; then the accumulated toxic component in queens decreases the fecundity of the colony. The key for the efficacy of bait is whether or not the insecticide is transferred to the queen. Successful eradication still needs to involve bait application although bait is quite expensive. The bait used in the US Australia includes Fipronil, Pyriproxyfen, Spinosad, Hydramethylnon, Fenoxycarb, and Methoprene.

Because of a lack of bait available in Taiwan , the Bureau of Animal and Plant Health Inspection and Quarantine, Council of Agriculture, Executive Yuan has imported 3 kinds of bait from the US for emergency purposes.

1.      Fipronil: Interferes with the nervous system of fire ants through contact and feeding. Significant results may be shown after 2~6 weeks of application.

2.      Pyriproxyfen: An IGR which prevents eggs from hatching. Significant results may be shown after 1~4 weeks of application.

3.      Spinosyns: A neural toxicant for fire ants which causes muscle convulsions, paralysis, or prostration. Significant results may be shown after 1~5 weeks of application.

Methods and considerations for bait application

Frequency of application: 2~4 times per year.

Dosage: 0.015% Spinosyns bait ( 2.8 kg /ha); 0.00015% Fipronil bait ( 1.7 kg /ha); 0.5% pyriproxyfen bait ( 1.7 kg /ha).

Application method: Broadcast bait in a large area or treat individual mounds in a small area (broadcast bait around the mound; 25 g /mound).

Use fresh bait: It is preferable to use an unopened container of bait or a container which has been tightly sealed and not stored for a long period (most bait container labels suggest its use within 3~6 months after first opening).

Apply when forager ants are actively searching for food. This can be tested by placing a small amount of bait near an active mound. If ants begin to remove the bait within 10~30 minutes, then that is a good time to use the bait. Ants are less active during cold and hot periods (when the soil temperature is less than 35 °C or greater than 21 °C ).

Do not disturb mounds before application. Apply when the ground and grass are dry and rain is not expected for the next 12~24 hours.

Step two: Individual mound treatments

Chemical and non-chemical methods may be used for treatment of individual fire ant mounds. It is better to apply the individual mound treatments 7~10 days after bait has been broadcast. Dusts, liquid drenches, granules, and aerosols are all examples of contact insecticides. As a contact insecticide, these products must actually come into direct contact with the ant.

i. Dusts

Apply chemicals formulated as dusts by following the label instructions. Ants will carry the dust on their bodies and transport the insecticide into the mound when walking through treated soil. Within a few days, the entire colony should be killed. To use a dust, distribute the recommended amount evenly over the mound Products include those containing 75% acephate (Orthene® Fire Ant Killer and Orthene® 75S), 15% acephate (Velocity®), deltamethrin (Deltadust® and Eliminator® Ant Killer Dust), and cyfluthrin (Bayer Advanced Lawn™ Fire Ant Killer).

Granules

To treat a single mound, do not disturb the mound. It is recommended to measure the required amount in a measuring cup and sprinkle it around the mound. Use a sprinkling method that  breaks the water stream into droplets and pour 4~8 liters of water over the treated mound if the label states the product needs to be watered in.

Acephate (Pinpoint® 15), bifenthrin (Talstar®), deltamethrin (Deltaguard™ G), permethrin (Spectracide® Bug Stop Insect Control Granules), and diazinon are all examples of granular contact insecticides labeled for fire ant control.

Liquids

Some products should be diluted with water and then applied to the mound. These liquid mound drenches kill the ants underground but must be applied in sufficient volume. It is recommended that application penetrates the entire nest using 4~8 liters of a diluted mixture poured over the top of each mound (Fig. 5). Be sure to wear rubber gloves to avoid contact with the chemical when handling liquid concentrates

Orthene®, Talstar®, Sevin®, Conserve* SC, and diazinon are examples of liquid contact insecticides.

In order to control the fire ant, the BAPHIQ has issued some contact insecticides as emergency chemicals as listed in the following table.

A: Follow standard procedures for broadcasting the chemical evenly over the infested area and subsequent watering. Subsequently, irrigate regularly.

B: If an emulsifiable concentrate, wettable powder, or suspension concentrate is used, it should be diluted with 4~8 liters of water and poured onto the top of the mound or 30 cm around the mound. It is better to allow the water to penetrate into entire mound. If granules are used, spread them evenly on the top of or around the mound, and then apply water if suggested.

Non-chemical control

i. Control using boiling water

1. Pour boiling water into every mound, as it can kill almost 60% of individuals.

2. Use at least 5 to 6 liters of water per mound. The boiling water should reach every corner of the mound.

3. A single treatment of a mound is not sufficient to control fire ants, but 5~10 days of continuous treatments are required; however, RIFAs can return to the same mounds again.

4. One needs to pay attention to protection measures during the treatment process, and protect all plants around the mounds from burning injuries.

ii. Control by flooding

Another non-chemical control of fire ants is flooding. It can drown ants, but it cannot remove mounds. For this control method, first excavate a mound from the soil. Then put all of the material in a bucket filled with water. After 24 hours, almost all ants in the mound will have died. Operators can face serious attacks from ants when excavating mounds. Therefore, they should be careful when carrying buckets containing mound materials. For those reasons, operators need to wear gloves, or use insecticides to reduce the chances of being bitten by escaping ants. The disadvantage of this method is that it is not suitable for larger invaded areas.

iii. Biological control

In the US , researchers have obtained some initial results using a biological method of RIFA control, but this technique is still not mature. It is believed that two biological control agents, a microsporidian and a parasitic phorid fly, native to South America have the potential to control RIFA populations. Although biological control techniques cannot eradicate RIFA, they can reduce populations, and make local ant species more competitive.

1. Parasitic fungus: Microsporidian

Microsporidians are transferred from infected workers to the queen. Infection by this fungus causes reductions in weight and the egg-laying capacity of a queen which becomes progressively weaker with time.

Microsporidians can be transferred from infected workers to larvae, and mature queens can also be infested. After 3 months of microsporidian application, populations will have decreased and may be eradicated within 9~18 months. Researchers have found that some polygyne queens cannot be infected by microsporidians because of their special immunity system. Microsporidians were first observed in South America in 1973, and were colonized in the US in 1996. The main reason for using microsporidians to control RIFA is that it only infects RIFA and BIFA. Microsporidians are species specific, so they are not known to infect other local ant species.

2. Parasitic phorid fly

Parasitic phorid flies can lay their eggs on the body surface of RIFA workers. Maggots of the phorid fly feed on the head of the workers and detach the head from the main body. Phorid flies pupate in the head of workers, and adults emerge after 4 weeks of pupation. Parasitic phorid flies can seriously affect and reduce the foraging behavior of a RIFA population. Parasitic phorid flies can easily be reared using the RIFA as a host.

3. Control using liquid nitrogen

        This method uses liquid nitrogen at -196 °C   to freeze fire ants to death. In this method, high-pressure liquid nitrogen is pumped into most tunnels and spaces in a nest, and one can expect 100% fire ant population control by freezing the entire nest.

Advantages

1. Protects the environment: Nitrogen is collected from the air and liquefied. It has no smell or taste and disperses in the atmosphere after changing back into a gas.

2. Immediate and rapid action: RIFAs die within a very short period of time.

3. Efficient: It can kill almost all individuals in a nest.

4. Unaffected by weather: It works very effectively after a rain.

Disadvantages

1. One needs to know the location of mounds during the early stage, and it is sometimes very hard to locate nests in order to control the RIFA.

2. One needs to treat 1 colony at a time. Single equipment can only control 1 mound at a time. Therefore, this method cannot be used for a larger invaded area within a short time period.

3. Liquid nitrogen is more expensive. The liquid nitrogen control method is the most expensive technique compared to all other currently used techniques for a single mound. This technique will substantially increase the costs of control.