Background

I am an engineer by profession—and a hobbyist gardener by choice—living in Coimbatore in Tamil Nadu, India. I have been growing vegetables in my home garden for about sixteen years, and, for the last decade, have been careful to use only organic fertilizers and pest control measures. In this blog I recount my experiences in countering tropical fire ants in my garden.

The tropical fire ant Solenopsis geminata¹

Tropical fire ants or Solenopsis geminata are a highly aggressive and invasive pest [1–6]. Ants are usually found on plants as protectors of sap-sucking insects like aphids. But the tropical fire ant can also cause direct and severe damage to plants. Even if the aphids are controlled, the persistent fire ants will start chewing through the tender stems, shoots, and roots of plants like brinjal, okra, snake-gourd, and even mustard greens, to name just a few. The affected plants will suffer visible damage and wilt; the hardier ones will recover, but the others will become unproductive or die.

The ant’s bite can be quite painful, and one member of my family suffers an allergic reaction if bitten. Figure 1 is a representative image of a fire ant attacking the forearm.

For the better part of a decade I have been looking for ways to organically curb this menacing pest.

Diatomaceous earth

I tried diatomaceous earth as a possible organic measure to control Solenopsis geminata. I used to sprinkle the powder near the holes around ant mounds and at the base of the stems of susceptible plants. While the tropical fire ants assiduously avoided the diatomaceous earth, there was no significant reduction in their numbers or their marauding activity. It chases the ants away but does not get rid of them. My plants still used to transition from lush and productive to wilted and barren, though perhaps less often than before.

Other less effective measures were to paint the lower stems with very small amounts of neem oil or petroleum jelly. Neither measure was effective.

I will now digress to a more recent experience where the tropical fire ant invaded, not a patch of earth, but a basin of water in which I was growing lotus plants.

Invasion of lotus basins

I grow lotus in small plastic basins in my garden, and the water surface is usually covered with duckweed or Lemna, which protects the water from excessive algal growth and also keeps it relatively clean and oxygenated.

One day, I found fire ants skating over the water surface, using the “skin” provided by the duckweed. This infestation of my lotus basins by tropical fire ants was the proverbial last straw that broke the camel’s back.²

Enlisting the power of AIs

I decided to harness the power of free (no cost) AI to defeat the tropical fire ant. My first port of call for help was Google AI Mode. This engine is also called Google Overviews. Such AI engines can be quite helpful in solving everyday problems, as in this case, helping me to shoo away the tropical fire ants from my garden.

Later on, I sought the help of the more powerful Google Gemini to get a more complete picture of the pest, and an introduction to methods that could better vanquish it.

The dialogue I had with these AIs is a rather convoluted one. Rather than recount that journey in tedious and linear detail, I will start with the solution proposed by the AI—which I adopted—followed by my observations, and comments on how to go forward.

Beauveria bassiana to the rescue

The AI recommended—with great certainty—a biocontrol agent, and said that it would solve my problem.³ It told me that a fungus⁴, when watered down the holes of anthills, would be carried by worker ants to infect and remove the queen of the colony. Such sanguinity is characteristic of AIs in general, as I believe that they are programmed to project confidence, by promoting their solutions as definitive, even if there is not much justification for it. So, beware of this limitation when using AIs.

The recommended biocontrol agent Beauveria bassiana [2] is an entomopathogenic fungus. It was suggested by an AI as an organic toxin to counter the tropical fire ant, while remaining relatively harmless to other insects, fish, and humans.

Application protocol

1. Buy Utkarsh Beveros-P Beauveria bassiana which is a 1.15% wettable powder of Beauveria bassiana with \(1 \times 10^8\) colony-forming units (CFU) per gram minimum from the strain BB-ICAR-RJP with Accession number MCC 1022. Alternatively, one could buy a product of similar quality and pedigree. The package I used is shown in Figure 3.

2. Mix 5 to 10 g (one to two teaspoons) of the powder in 1 L of water. Mix well before application.

3. Deeply drench the ant holes, ant mounds, and surrounding soil around 18:00, when the sun is just setting, as the fungus does not survive harsh sunlight.

4. Repeat each week for three weeks to ensure that eggs and larvae are controlled as well.

Observed results

There was a noticeable reduction in the number of ants patrolling the drenched areas. However, they returned within five days to a week. So, the frequency of drenching was increased to twice a week.

After application, the ant mounds usually moved from one to two metres away from their previous locations. But the ants still prevailed.

Tropical fire ants can have a subterranean nest connected by tunnels that open out at different places on the ground. Once an opening is attacked, they will open other ant holes as entrances and exits to their nest.

Unintended consequences

Concurrent with the disappearance of the ant mounds from certain areas of my garden, there was an invasion of my home by these little critters. Basically, when the going got tough, the tough got going.

Impractical solutions

Because AIs are not infallible, several measures initially suggested by the AI were later deemed impractical or ineffective, on closer questioning of the same or a more powerful AI. To be grounded in reality, and for the sake of completeness, I enumerate two of these false starts below.

1. Phorid Flies (Pseudacteon species): These were suggested as a biocontrol. But they are not available in India as an agricultural resource, although they are used in the US and Australia. Therefore, a non-starter.

2. Larger Native Ants (Diacamma rugosum/Queenless Ants): These are natural predators for the tropical fire ant, but their presence will be more by happenstance than design. Impractical to implement in a home garden.

Papers on controlling Solenopsis geminata

Solenopsis geminata has the dubious distinction of being a member of the Global Invasive Species Database.

Despite this, the primary and review literature on Solenopsis geminata is not copious. Indeed, one survey from 2023 on pest ants states:

The virulence of Solenopsis geminata as marauders who lay waste whole plants, and possibly beds of plants, is described thus:

While synthetic pesticides have been advocated as an effective solution [4, 5], the quest for a sustainable organic slution has not resulted in a definitive biocontrol protocol that may be repeated reliably.

The road ahead

The principal biocontrol method for Solenopsis geminata discussed in this blog, uses Beauveria bassiana drenches on the soil around ant mounds and holes. It is at best a temporary, palliative measure. As Macbeth famously says in the eponymous Shakespearean play Macbeth Act III, Scene 2, “We have scotched the snake, not killed it.”⁵

Spinosad

One means to eradicate the tropical fire ant, suggested by an AI, is to use a solution of Spinosad [7, stearnes-2021?] concocted into a bait with the addition of oil, sugar, and some slurry. When the bait is dutifully carried by workers to the Queen, it leads to her death and the collapse of the colony.

The room for doubt that this method might not be entirely organic, and the complexity in its application, did not appeal to me as a hobbyist gardener. However, it holds the attractive prospect of pest eradication that is at a whole level above the hit-and-run palliative measures talked about in this blog.

Botanicals and essential oils

Perhaps, one light at the end of the tunnel is the forward-looking investigation of botanicals and essential oils as biocontrols by Nalini and Sasinathan [3]. Botanical agents like clove, cinnamon, and coriander powder, and essential oils like peppermint, clove, and eucalyptus are well-researched entities, compatible with organic pest control. If intensive laboratory and field research is undertaken in the near future, we might well be on the road to organic eradication of the pest Solenopsis geminata. I can already visualize diatomaceous earth imprgnated with a cocktail of essential oils and a possibility.

Chanda and Munda

Measures for Lotus pond

I followed up by asking the AI how to rid my lotus ponds of the fire ants. The AI logically answered that I should reduce the surface of the water covered by duckweed so that the ants could not skim the water surface with impunity. I was also advised to ensure that there was no overhanging vegetation that could give the fire ants “visa-free” access to my lotus ponds.

Chanda and Munda Use an insect enemy.

Future directions/Looking ahead

The research is not mature enough for one or more definitve biocontrol methods to be confidently prescribed.

Other fungi.

Ants Chanda/Munda

Flies Vrtrasura etc.

Essential oils and spices.

Essential oil impregnated diatomaceous earth. etc.

Ultrasonic, infrared or other mapping of the subterranean nests with focused measures to be rid of the pest.

Ants deported from the garden will find their way into the home. Lesser of two evils?

From palliation to eradication: Spinosad. Hesitation.

Acknowledgements

Feedback

Please email me your comments and corrections.

A PDF version of this article is available for download here:

References

•  Beauveria bassiana (1)
•  biocontrol (1)
•  brinjal (1)
•  fire ant (1)
•  greens (1)
•  okra (1)
•  Solenopsis geminata (1)