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 pumped-up hype being used for an ulterior motive.
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.
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 used, and they contain different treatments. The baits consist of a "carrier" of coarse ground (1-3mm) corn grit soaked in soyabean oil, and specific chemicals.
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 with a month or so.
The 2 types of baits use different treatments, either:
Long-term, broad-area treatment: Insect Growth Regulator s-methoprene or pyriproxyfen
Fast acting, topical treatment: Insecticide Indoxacarb or a combination of hydramethylnon and pyriproxyfen
Who controls the use of chemicals in Australia
The use of chemicals such as fire ant treatments is strictly controlled by the APVMA. The APVMA approves permits 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.
APVMA's role is to ensure that the use of chemicals is governed to ensure public safety and integrity of our food chain and natural environment.
How toxic are these chemicals
Chemical toxicity is measured using "LD50" 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.
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.
The primary concern here is indoxacarb as it is 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.
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 wide area.
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 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 knowledge, honey bees can not / would not access fire ant bait as a food source, so this is extremely unlikely to be a source of poisoning.
However, there are some possible ways that fire ant poisons could be accessed by bees:
Contamination of water sources
Unlikely for moving (fresh) water sources as the contaminants would be washed away and diluted very quickly.
Possible for still water sources such as puddles, billabongs, dams, and dry creek beds.
Possible for still water sources around homes such as pot plant trays, pet water bowls, and other items that may contain water.
Open containers that have been used to store fire ant baits
It is possible that the smell of corn grit and soyabean oil may attract bees, though unlikely in normal circumstances
If attracted to an empty container, bees may be contaminated by poisons and return to the hive.
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.
Open containers that are storing fire ant baits
As above, bees may be attracted to the smell of corn grit and soyabean oil
It is possible that they may enter an open container of poison and become contaminated before returning to the hive
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.
Spillage of fire ant baits in concentrated piles
If the bait was spilled in larger amounts and not cleaned up, this could pose a risk.
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.
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.
Comments