Red Imported Fire Ants (RIFA) are invasive insects known for their painful stings and the significant damage they can cause to human health as well as pets, wildlife, and even agriculture. Managing these invasive ants is primarily done using liquid insecticides and granular baits. Here we will discuss each:
1. Granular Baits
Granular baits are widely used for RIFA control in the U.S. and elsewhere. These baits consist of an active ingredient combined with soybean oil and corn grits. Worker ants carry the bait back to their colony, sharing it with other members, including the queen(s) and larvae.
Advantages:
- Highly effective: Granular baits are highly effective in managing and eradicating RIFA colonies. Since these baits are non-repellent, RIFA workers readily feed on them and transport them back to the colony where they share the bait with the queen(s) and larvae.
- Long-Term Control: Unlike liquid insecticides, granular baits target the entire colony, including the queens. This phenomenon makes it more difficult for the colony to recover from the treatment. Depending on the active ingredient, baits provide control that can last for months, significantly reducing the chances of re-infestation.
- Less Labor Intensive: Unlike mound drenching and soil and turf spraying, granular baits are easy to apply and can be broadcast over large areas with minimal effort. Using motored spreaders can significantly speed up the application process.
Disadvantages:
- Slow Acting: The primary drawback of granular baits is their slower speed of action. Depending on the active ingredient and colony size, it can take one to several weeks to see noticeable results.
When to use: Granular baits are ideal for managing widespread infestations or for those seeking longer-term control with minimal labor. They are particularly effective when used as part of a preventive strategy or integrated pest management (IPM) plan. They pose a lower risk to mammals and birds and are less likely to be introduced to water bodies during rain or irrigation.
2. Liquid Insecticides
Liquid insecticides can be used to address visible RIFA colonies quickly. This method involves applying insecticide solutions directly to the mounds or treating larger areas with soil and turf. Here’s an overview of their pros and cons:
Advantages:
- Fast Action: Liquid insecticides provide rapid results, often killing visible ants within hours or days. The speed of action makes liquid insecticides a popular option when immediate control is needed such as near public events.
Disadvantages:
- Colony Splitting (Budding): One of the biggest challenges with liquid insecticides is the risk of colony fragmentation. The treatments rarely eliminate the queen(s) and the colony may split into smaller satellite colonies.
- Labor Intensive: Applying liquid insecticides requires mound drenching or spraying the ground which can be physically demanding and time-consuming, especially in large areas.
- Limited Long-Term Effectiveness: While effective in the short term, liquid insecticides often fail to provide lasting control because they don’t target the entire colony, including queens and larvae deep underground.
- Environmental hazards: Applying liquid insecticides to large areas can pose a risk to the environment via pesticide run-off. Pyrethroids and other pesticides can damage aquatic life in urban and agricultural areas and can end up in lakes and oceans.
When to use: Liquid insecticides must be used only for emergencies or when immediate control is required. However, they are not ideal for achieving long-term control of RIFA populations.
Other methods: Recently, fire ant decapitating phorid flies were successfully established in California for the first time (Oi et al., 2019). These include Pseudacteon curvatus and Pseudacteon obtusus (Diptera: Phoridae), both of which require RIFA workers in order to reproduce. Previous efforts failed to establish these flies in the arid California climate.
Fire ant decapitating flies, primarily from the genus Pseudacteon, are small parasitic flies native to South America and are natural enemies of fire ants, including the invasive Red Imported Fire Ant (Solenopsis invicta). These flies exhibit a fascinating life cycle: adult females locate fire ant workers and inject a single egg into the ant’s body. The egg hatches into a larva, which migrates to the ant’s head, feeding on its internal tissues. Eventually, the larva causes the ant’s head to detach, earning the fly its “decapitating” name. The larva pupates inside the severed head and later emerges as an adult fly. These flies are highly specific to fire ants and do not harm other species, making them an important biological control agent. Although they rarely eliminate entire colonies on their own, their presence disrupts ant foraging behavior, reducing the colony’s ability to gather resources and thrive.
Other biological control agents include Solenopsis invicta virus 3 (SINV-3), and the microsporidian fire ant pathogen Kneallhazia solenopsae.
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