Fire ant baiting and bee hives

There have been a lot of anecdotal claims about the impact of fire ant baiting on bee hives. These claims often contain a lot of emotion and a lot of hype, so much so that it is difficult to sort through what is accurate and what may be pumped-up hype being used for an ulterior motive.

Very few, if any, of these claims are supported by objective, measurable, and confirmable data that supports the claims being made. This is the critical point. It is easy to make unsubstantiated claims, but for anyone who believes in scientific process and rational thinking, Hitchen's Razor applies: that which is asserted without evidence can be dismissed without evidence.

In this post I want to examine some of the background, delve into the chemicals and risk factors, and talk about my experience as a beekeeper in a fire ant eradication zone. Importantly, unlike many on facebook and other communities, I will make no unsubtantiated claims.

Fire ant baiting

First, let's look at the chemicals used.

The Fire Ant program website lists the data of chemicals they use. You can find their page here.

There are 2 types of bait each containing different chemical treatments. The baits consist of a "carrier" of coarsely ground (1-3mm) corn grit soaked in soyabean oil, with specific chemical treatment additives.

Firstly, there is a long-term control formulation, used for wide-spread coverage at very low dosage. This application controls nests over 1-4 months.

Secondly, there is a fast-acting treatment used to dose individual nests and aimed at eliminating the nest within a shorter period of time, ie about a month or so.

The 2 types of baits use different treatments, either:

1. Long-term, broad-area treatment: Insect Growth Regulator s-methoprene or pyriproxyfen
   

2. Fast acting, topical treatment: Insecticide Indoxacarb or a combination of hydramethylnon and pyriproxyfen

NOTE: This information was taken from the Fire Ant website in mid-2025. Chemical treatments and various other operational details may have changed since that time.

Who controls the use of chemicals in Australia

The use of chemicals such as fire ant treatments is strictly controlled by the Australian Pesticides and Veterinary Medicines Authority (APVMA). The APVMA approves permits and product registrations for treatments under very specific label conditions. Any use of these chemicals that breaches the label conditions requires a separate permit or is illegal and can result in legal action.

The role of the APVMA is to ensure that the use of chemicals is governed to ensure safety and integrity of our food chain and natural environment.

How toxic are these chemicals

Chemical toxicity is measured using "LD50" (or LC50) data. LD50 is the amount of a chemical required to be lethal to 50% of the test population, also known as the "median lethal dose". It is often expressed in milligrams per kilogram of body weight (mg/kg). Lower values for LD50 indicate higher toxicity of a substance. LD50 values vary for different species; some species are more sensitive to a substance than others.

Generally, poisons are selected to target specific species while having lower toxicity for non-target species. However, it is important to remember at all times that many seemingly harmless substances can be harmful if the dose received is sufficient. Even pure water has an LD50 rating!

Let's look at the LD50 values for the fire ant bait chemicals for honey bees (this data can be easily found on a variety of websites using a google search).

Chemical	LD50 for bees	Comments
S-methoprene	10mg/kg or 1000ug/bee	Practically non-toxic to adult bees, but can affect larval development.
Pyriproxyfen	more than 1mg/kg or 100ug/bee	Practically non-toxic to adult bees, but can affect larval development.
Hydramethylnon	0.68mg/kg or 68ug/bee	Practically non-toxic to adult bees.
Indoxacarb	0.0024mg/kg or 0.24ug/bee	Highly toxic to bees when ingested.
Fipronil	0.0019mg/kg or 19ug/bee	Not specifically listed by the Fire Ant Eradication Program, but a common insecticide used in ant killers and HIGHLY toxic to bees.

Sources: APVMA, US EPA, US NPIC, ECHA

Toxicity to honey bees

Are these chemicals toxic to honey bees, the short answer is obviously yes. If used incorrectly, these chemicals would be toxic to bees and many other species if they received a sufficiently high dose.

Digression:

Did you know that water is lethal to humans? While there is no official LD50 for water, it is estimated to be around 7 litres consumed rapidly. This leads to "fatal water intoxication" (hyponatremia) by diluting blood sodium, causing brain swelling and potential coma and/or death. So even benign chemicals can have toxicity when applied incorrectly.

The primary concerns amongst the fire ant chemicals are indoxacarb and fipronil (widely used as a general pest treatment in the urban environment). These are both highly toxic to bees. The rest of the poisons are "practically non-toxic" to adult bees and only affect larval development, which a colony can generally recover from in time, assuming the contamination source is short-lived.

NOTE: The primary complaints about bees being affected by fire ant treatments relate to baiting (aerial application and manual application). As we can see already from the data above, these baits are "practically non-toxic" to bees.

How might bees access fire ant bait chemicals?

The chemicals are impregnated into "coarse corn grit" that is 1-3mm in size, and distributed on the ground over a broad area at a very low rate of application.

Foraging honey bees source food resources from flowering plants and water from the environment. They seek out nectar and pollen sources for food, and water sources for hydration. Foraging honey bees do not eat or process the resources they collect, they store it on their body or in their honey crop and return to the hive.

Bees are not physically capable of, nor the least bit interested in, collecting coarse corn grit as it does not stick to their body like pollen. They do not collect large material in their mouths as a food resource (unlike ants).

Based on this, honey bees can not / would not access fire ant bait as a food source. If so, then fire ant baiting is extremely unlikely to be a source of poisoning.

How much bait would be needed to kill a modest sized colony?

Considering the bait formulation of 5g/kg of s-methoprene, how much bait material, based on the LD50 values above would be required to kill a modest-sized bee colony of 20,000 bees (1 full brood box)?

The LD50 is 1000 micrograms per bee ie sufficient to kill 50% of the test sample.

Therefore, a colony of 20,000 bees would need to collect at least 20g to kill 50% of the population. This equates to 4kg of bait collected.

To kill the entire colony would require around 8kg of fire ant bait to be collected.

This does not just seem unlikely, it is practically impossible.

However, there are some possible ways that fire ant poisons could be accessed by bees:

1. Contamination of water sources

   1. Unlikely for moving (fresh) water sources as the contaminants would be washed away and diluted very quickly.

   2. Possible for still water sources such as puddles, billabongs, dams, and dry creek beds.

   3. Possible for still water sources around homes such as pot plant trays, pet water bowls, and other items that may contain water.
      

2. Open containers that have been used to store fire ant baits

   1. It is possible that the smell of corn grit and soyabean oil may attract bees, though unlikely in normal circumstances

   2. If attracted to an empty container, bees may be contaminated by poisons and return to the hive.

   3. It is unlikely that a sufficient number of bees would be affected such that a sufficient dose of poison was returned to the hive to have harmful consequences.
      

3. Open containers that are storing fire ant baits

   1. As above, bees may be attracted to the smell of corn grit and soyabean oil

   2. It is possible that they may enter an open container of poison and become contaminated before returning to the hive

   3. Again, it is unlikely that a sufficient number of bees would be affected such that a sufficient dose of poison was returned to the hive to have harmful consequences.
      

4. Spillage of fire ant baits in concentrated piles

   1. If the bait was spilled in larger amounts and not cleaned up, this could pose a risk.

   2. Bees may be attracted to the bait and become contaminated before returning to the hive. It is possible that if the bait was not cleaned up, enough bees could be exposed to lead to harmful outcomes for the hive.

   3. Alternatively, a pile of bait left in the open could be washed by rain or irrigation into water sources that bees depend upon. This might lead to sufficient doses to cause harmful outcomes for the hive.

My experience so far

I am a semi-commercial beekeeper with a moderate number of hives operating in heavily treated fire ant eradication zones.

I have had zero losses attributable to fire ant baits.

As a contract beekeeper who manages about 100 hives for a commercial beekeeper in similar fire ant eradication zones, I have experienced zero losses attributable to fire ant baits.

Working with many clients whose hives are in fire ant eradication zones, I have experienced zero losses attributable to fire ant baits.

I am aware that there are concerns, and some people claim that "hundreds" of hives have been lost to fire ant bait poisons. I am sympathetic to beekeepers who have lost hives, it is an emotional and economic loss that can sometimes be very difficult to deal with.

However, the available evidence and the nature of bee foraging indicate that poisoning from fire ant bait is extremely unlikely. Losses are more likely caused by other factors such as unrelated/careless use of household poisons, careless commercial insecticide treatments, starvation, or pests and diseases. The latter issues have been prevalent towards the end of the '23-'24 season with poor forage due to extended wet weather throughout late summer and autumn.

Conclusion

Poisons are dangerous! They should always ALWAYS be used only as directed and with extreme caution and care for the environment.

Poisons can be harmful to bees in many ways. Use of poisons around bee hives and within the foraging area (up to 20 square km) should only be done with extreme care.

There is no direct evidence that fire ant baiting programs have directly affected bee hives. Based on bee behaviour, empirical and anecdotal evidence, and knowledge of the application methods and chemicals used in fire ant baiting programs:

• It is extremely unlikely that wide-area fire ant bait application will have any negative effect on bee hives.

• It is unlikely that topical application of fire ant poisons to specific fire ant nests will have any negative effect on bee hives.

It would be wise to treat claims of harm to bees and losses of bee hives directly attibuted to fire ant baiting seriously, no matter how unlikely. Rigorous investigation is required, with pathology testing to assess toxin presence, before any root cause is confirmed.