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Response to Little Fire Ants (LFA) in Nahiku


Here are the roles of various agencies involved in the Little Fire Ants (LFA) infestation in Nāhiku (east Maui):

  • Hawaii Ant Lab (HAL): Based in Hilo, HAL is the entity in Hawai‘i with the most expertise regarding little fire ants. HAL sets treatment protocols and directs overall operations for LFA infestations on Maui and elsewhere in the state. HAL staff comes to Maui to manage application of insecticides at infested sites.
  • Maui Invasive Species Committee (MISC): Works cooperatively with other agencies to draft and implement operational plans. MISC staff conducts delimitation surveys at known infestations and early detection surveys elsewhere on the island. In Nāhiku, MISC staff cut transects for survey and control operations and occasionally assists with pesticide application under HAL’s guidance. MISC takes the lead in working with affected landowners (secures permission, communicates about schedules and provides progress updates). MISC also conducts outreach about LFA on Maui and Molokai.
  • Hawaii Department of Agriculture: Participates in planning exercises; conducts LFA surveys at ports and harbors; conducts or assists with surveys at suspect locations; and oversees pesticide use to ensure labels are being followed.
  • County of Maui: Funding for LFA work. Actively interested in status of infestations.
  • Hawaii Department of Land and Natural Resources: State funding for MISC/HAL.
  • U.S. Fish and Wildlife Service:  Becomes involved if activities have the potential to impact species listed under the Endangered Species Act.

Our current understanding is that the pesticides being used for eradication of LFA are restricted and CANNOT be used within 50 feet of a stream bed. 

No, none of the pesticides used to control LFA in Nāhiku are restricted. The pesticides used to date are Tango and Siesta. Both pesticides were used during the initial 2 treatments and all subsequent treatments have been Tango, though they plan to use Siesta again in the near future. Both pesticides are classified as general use pesticides and are being used in accordance with the labels.


Siesta is a sodium blocker insecticide (active ingredient is metaflumizone) that causes the cessation of feeding, increased immobility and ultimately death. It has a very low toxicity for humans or pets and remains attractive to the ants even after it gets wet. It is a bait insecticide; the workers carry it back to the nest and feed it to the queen.

Tango (active ingredient S-methoprene) does not kill the ants directly; it is an insect growth regulator which prevents the larvae from developing into adults and slows down or stops the queen from laying eggs. Eventually the colony dies as workers are not replaced.  Tango is purchased as a concentrate which is then mixed with a gel bait chosen by the applicator (powdered beef liver and corn oil, in the case of LFA); the workers carry the bait back to the queen. 

The Hawaii Ant Lab has published an extensive fact sheet, Mixing Hal Gel Bait With Tango For Control Of Little Fire Ants.

USE NEAR WATER: None of the pesticides are registered for use in water but actual guidelines vary by pesticide and application method. Both the bait products being used have different instructions for use near water. 

Tango, for example, has this instruction on the label “Do not apply directly to water or to areas where surface water is present.  This means it can be used near water but not applied directly to water. 

Siesta, on the other hand, instructs the user: “Do not make broadcast application within ten feet of perennial fresh water.” 

So, Siesta will not be used near the streams. Interestingly, the active ingredient in Tango, S-methoprene, is commonly used as a mosquito larvicide to stop the spread of West Nile Virus.

Due to the nature of the stream, littered with boulders and large stones, we will need to think carefully about how to apply baits in this situation. 

Currently, Hawai`i Ant Lab is working with the HDOA Pesticide Branch to make sure anything they do is allowed under the label. 

A network of streams run through the infested properties, which has helped spread LFA downhill. Treatment of these areas will be part of our Phase II operations but will not proceed until there is a pesticide approved for treating ants in water. We anticipate that treatment will probably use the same active ingredient as Tango (as noted, already approved as a mosquito larvicide). 

The Hawaii Ant Lab has a great summary of pesticides available that can be used to control LFA, along with links to the MSDS on their website.

What State of Hawaii Agency or United States Agency has authority in this pesticide use issue?  Our current understanding is enforcement authority and oversight of pesticide use is with the Hawaii State Department of Land and Natural Resources (DLNR) or the U.S. Fish and Wildlife Service.   Please clarify which agency or agencies are responsible and have legal authority in detail.

See above for a brief overview of agency responsibilities. Registration and use of pesticides is administered by the federal Environmental Protection Agency. All pesticides must be registered with the EPA. Some state laws also govern pesticides and their use. State registration of pesticides and pesticide use is administered by the Hawaii Department of Agriculture Pesticide Branch.

Additional laws that may be relevant include the federal Clean Waters Act (CWA).  The CWA, in part, regulates pesticide use near waterways and the ocean. In Hawaii, the CWA is administered by the Hawai‘i Department of Health.  Depending on the circumstances, additional permits may, or may not be required.

The U.S. Fish and Wildlife Service conducted a survey for insects listed under the Endangered Species Act. There are two endangered damselflies known from East Maui: Megalagrion pacificum, and M. nesiotes.  Staff from the U.S. Fish and Wildlife Service, at the request of HAL, MISC and HDOA, conducted a survey of the main stream that runs through the infested area.   They did not find the listed damselflies in those catchments. They concluded that the stream structure did not suit these species; they also noted the presence of introduced invasive poeciliid fish species which feed on the larval stages.  HAL is working on permit requirements to allow treatment of LFA suitable habitat (e.g., moss-covered stones) within the stream bed.

It is our current understanding there is a fungus that is a natural enemy of LFA.   Please provide any information you can on this subject. Is the fungus available for use in controlling LFA?  Please explain in detail.

There has been a lot of press about the potential use of the Cordyceps fungus (an endoparasitoid, aka zombie ant fungus) to control LFA.  In general, the fungal/ant relationship is highly evolved and very host specific. A fungus that effectively controls one type of ant may not even infect another type, or if it does, the fungus may not spread effectively.

Some of the press about this as a possible solution may stem from research on fungus for control of red imported fire ant (RIFA, or Solenopsis invicta), which is not present in Hawaii. RIFA is a separate species, unrelated to the little fire ant. Typically effective natural enemies are highly host specific; it would be a big jump to assume this fungus would be effective with little fire ants. Even with RIFA, the fungus is most effective when spores are injected into a nest – it kills ants but not the entire colony. LFA do not have large easily locatable nests like RIFA. Scientists continue to look for a natural enemy to control little fire ants, but no likely candidates have emerged yet. In general, biological control of ants and other social insects is extremely difficult.  For example, there also is concern about the potential broad impacts of a fungal insecticide as it could affect other non-target species such as bees. Classical biological control is generally a tool for long-term management, not eradication. On Maui, we hope to eradicate LFA, not manage them long-term.

At present, we are not aware of this fungus being available for use against the little fire ant and we would not be able to support its use without answers to the questions posed above, especially with regard to potential non-target impacts. We hope that one day new tools and options will result from exploratory research, but before that happens, they will need to go through a rigorous testing process to make sure they are safe and effective.  Rushing that process is not a good idea.

Are there “less toxic” or “organic” alternatives to the pesticides currently in use?

One very important factor HAL considered when designing an eradication plan was the relative toxicity of control options.  For example, the entire area could have been sprayed with agricultural pesticides, but this would be an indiscriminate use and application.  Instead, the preferred approach was to use baits, which is much slower but orders of magnitude safer.

Some people push for use of an organic pesticide for little fire ant control, such as boric acid. Just as synthetic pesticides vary in levels of toxicity, the same holds true with organic pesticides. Boric acid is synthetically derived from mined boron, but it’s not necessarily a less toxic alternative to chemical pesticides, especially Tango. Boric acid can be highly toxic –it kills ants because it is a stomach poison. It’s poisonous to people (and pets) if taken internally or inhaled.

The Agency for Toxic Substances and Disease Registry states: The minimal lethal dose (LD) of ingested boron (as boric acid) was reported to be 2–3 g in infants, 5–6 g in children, and 15–20 g in adults.

Comparison of acute oral toxicity for different insecticides for LFA control (LD50 for a rat):

  • Boric Acid:                                                                   2,660 mg/kg
  • S – Methoprene (active ingredient in Tango):            >34,000 mg/kg
  • Metaflumizone (active ingredient in Siesta):               > 2,000 mg/kg

Boric acid is 12-13 times more toxic than the active ingredient in Tango. Tango is applied at 0.25% active ingredient while boric acid is used at 2-3%, making it substantially more toxic when applied. And though the LD50 for metaflumizone (Siesta) is comparable with boric acid, Siesta is applied at a rate of only 0.063% active ingredient.

I tried to calculate what this would mean in the field to give you an idea of the relative toxicity of the pesticides as they would be used. Basically in a single sitting, an average size rat would have to eat the following amounts to get a lethal dose of mixed bait: Boric acid bait=8.2lbs, Siesta bait = 244.7lbs, Tango bait = 1,049lbs.

Neither HAL nor MISC can legally apply boric acid for control of little fire ants without a permit from HDOA (find more detail about the labeling restrictions on the fact sheet below under “Legal Stuff.”) However, there is so much interest in it that HAL has developed a fact sheet with guidelines for using boric acid as well as other pesticides for control of LFA (for homeowners use). See a wealth of information on the Hawaii Ant Lab website, LittleFireAnts.com.

Of note is that while boric acid is approved for use on organic farms, it can only be used in a trap or in structures and cannot come in contact with the soil or food crops, according to the Hawaii Organic Farming Association (HOFA).

The HAL website includes a page that compares all available baits and their use limitations with links to labels and MSDS sheets.

Here’s a link to a PDF file regarding the use of boric acid in organic agriculture: http://www.ams.usda.gov/sites/default/files/media/Boric%20Acid%20TR.pdf

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