Neurotoxins

There are several classes of neurotoxins available for the control of invasive ant species. Two of the most commonly used are fipronil and indoxacarb. Other neurotoxins include those belonging to the class of neonicotinoids (also known as neonics) that are chemically similar to nicotine. and the synthetic pyrethroids, which mimic the naturally occurring neurotixns in chrysanthemum. Like all pesticides, there are potential non-target effects and human health concerns associated with the incorrect use of insect neurotoxins. It is important to consider these potential negative impacts in the specific environment you plan to treat before committing to their use.

Fipronil : Indoxacarb : Neonicotinoids : Synthetic pyrethroids : Other neurotoxins

Fipronil

Detailed information about fipronil and its fate in the environment can be found in this publication, which is summarized below.

Fipronil interferes with the transmission of nerve impulses in insects causing severe tremors, paralysis and then death. It is often used to control insects that are no longer affected by synthetic pyrethroids.

When treating ants it is important that the toxin is administered at low doses to allow poisoned workers sufficient time to pass the toxin on to their queen, the larvae and their nest mates.

Breakdown in soil

Soil absorption of fipronil increases with organic matter content and the compound is moderately prone to leaching.

The time it takes for half the fipronil to break down (the half-life of the chemical) is dependent on soil content, and ranges from 36 hours in the top 10 cm of soil and between 34 days in loamy soil to 194 days in sandy loam soils. However, when present, soil microbes break the chemical down in less than 10 days. Fipronil breaks down into several smaller compounds. Soil moisture influences the relative amounts of each of these compounds that break down into the soil.

Breakdown in water

In water, fipronil breaks down slowly (half-life of 123 days) without air. Because fipronil binds with soil that has a high organic content, residues of the compound and its break down products have been detected in freshwater sediments in both agricultural and urban areas of the United States. The insecticide is also comparatively stable in acidic to neutral (pH 7) water (half-life up to 100 days) where air is available.

However, fipronil is rapidly broken down in water by sunlight (half-life of ~7.5 hours - but accelerated in water under alkali conditions with a pH greater than 8). Break down by sunlight of fipronil in soil is slower depending on the level of absorption.

Non-target effects

Fipronil is highly toxic to a variety of aquatic species including water fleas, crayfish and some fish and it accumulates in the tissues of some species. Some of the products released by breaking down fipronil have been found to be three times more toxic to fish than the parent compound and six times more toxic to aquatic invertebrates.

Consumption of fipronil has been found to be toxic to some land birds and low level toxicity has been observed for mallard duck, pigeon, and field sparrows.

Fipronil is highly toxic to other insects and honey bees are particularly vulnerable. Fipronil based insecticides should not be used in a sugar based matrix where honey bees are present.

Crabs have been found to be susceptible to fipronil. One recorded programme of broadcast baiting in areas where crabs are highly abundant, required attractive lures to be dropped outside the treatment area to draw the crabs out of harm’s way.

Information sources

Boland Smith, Maple, Tiernan, Barr, Reeves, Napier. 2011. Heli-baiting using low concentration fipronil to control invasive yellow crazy ant supercolonies on Christmas Island, Indian Ocean. Chapter in Island invasives: eradication and management. Veitch, Clout, Towns, (eds.): pp 152-156.

Chaton, Ravanel, Tissut, Myran. 2002. Toxicity and bioaccumulation of fipronil in the nontarget arthropodan fauna associated with subalpine mosquito breeding sites. Ecotoxicology and Environmental Safety 52: 8-12

Connelly 2001. Environmental fate of fipronil. Report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Gunasekara,Truong. 2007. Environmental fate of fipronil. Report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Key, Chung, Opatkiewicz, Wirth, Fulton. 2003. Toxicity of the insecticides fipronil and endosulfan to selected life stages of the grass shrimp (Palaemonetes pugio). Bulletin of Environmental Contamination and Toxicology 70:533-540

Overmyer, Rouse, Avants, Garrison, Delorenzo, Chung, Key, Wilsom, Black. 2007. Toxicity of fipronil and its enantiomers to marine and freshwater non-targets. Journal of Environmental Science and Health Part B 42: 471–480

Pisa, Amaral-Rogers, Belzunces, Bonmatin, Downs, Goulson, Kreutzweiser, Krupke, Liess, McField, Morrissey, Noome, Settele, Simon-Delso, Stark, Van der Sluijs, Van Dyck, Wiemers. 2015. Effects of neonicotinoids and fipronil on non-target invertebrates. Environmental Science and Pollution Research (2015) 22:68–102

Tingle, Rother, Dewhurst Lauer and King. 2000. Health and environmental effects of fipronil. Briefing paper for the Pesticide Action Network UK

Indoxacarb

Detailed information about Indoxacarb and its fate in the environment can be found in this document, which is summarized below.

Indoxacarb is a neurotoxin that blocks the flow of sodium to nerve cells resulting in impaired nerve function causing paralysis and death. It may take insects days to die.

Breakdown in soil

Decomposition of indoxacarb in aerobic soil happens in two stages. The first stage takes approximately 4.5 days. The second stage takes around 43 days (at 25°C). Degradation is significantly slower at lower temperatures - for example, the process takes approximately two and a half times longer at 20°C. Degradation in anaerobic soils is also slower than in aerobic soils, with degradation taking approximately 186 days at 25°C. Break down by light in soil takes approximately 139 days.

Breakdown in water

The rate of degradation of indoxacarb in water is highly dependent on pH. In neutral water (pH 7), breakdown will take approximately 38 days. Breakdown is faster in more acidic water (pH5 >30 days), but is most rapid in alkali waters (pH 9 ~ 1 day). Break down in water is accelerated by light (e.g. half-life in water (pH 5) is ~3 days.

Non target effects

Indoxacarb is moderately to very highly toxic to freshwater estuarine /marine fish and insects, and moderately toxic to crustaceans. Indoxocarb has been observed to be moderately toxic to some land bird species (e.g. bobtail quail), but toxicity to mallard ducks was very low.

Information sources

Dias. 2006. Environmental fate of indoxacarb. Revised report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Meuller, Moretto. 2005. Indoxacarb. Draft toxicological report prepared for the Food and Agrculture Organization of the United Nations (FAO) Joint Meeting on Pesticide Residues (JMPR)

Neonicotinoids

Neonicotinoids, also known as neonics, are a class of synthetic neurotoxins, which are chemically similar to nicotine. Neonicotinoids are used extensively in agriculture as a systemic insecticide - they are highly soluble in water and move freely through plant tissues, meaning the whole plant is protected from insect herbivores after the seed or roots have been drenched.

In addition their toxicity to mammals is very low compared to their effect on insects. However, they have been linked with colony collapse disorder in bees and to declines in insectivorous bird populations because of the sharp reduction in insect numbers associated with their use.

The legitimacy of these links have been questioned by manufacturers, but concern over these non-target effects led the European Union to restrict the use of neonicotinoids. Three commonly used neonicotinoids are dinotefuran, imidacloprid and thiamethoxam.

AGCARM. 2013. Fact sheet on Neonicotinoids. Factsheet produced by New Zealand Agricultural Chemical and Animal Remedy Manufacturers Association.

Dinotefuran

Breakdown in soil

Dinotefuran is expected to be highly mobile in soils, indicating potential for leaching and groundwater contamination. In aerobic soils, half of the compound will be degraded in 81.5 days.

Breakdown in water

Dinotefuran is highly soluble in water and remains stable in neutral to alkali conditions. The main route of degradation in water is by sunlight. It takes approximately 1.8 days for half of the toxin to be degraded by sunlight in waters shallower than 2 m, though it is uncertain how long the dinotefuran takes to degrade in deeper waters.

Non target effects

Dinotefuran has low to very low toxicity to birds and low toxicity to fish and crustaceans. Dinotefuran is highly toxic to bees and this toxicity is both acute and cumulative. Dinotefuran is highly soluble and travels freely through plant tissue.

Information sources

Anon. 2004. Dinotefuran. Pesticide Factsheet produced by the United States Environmental Protection Agency

Imidacloprid

Breakdown in soil

Imidacloprid is highly soluble in water and binds poorly with soil, suggesting a tendency to leach. However no evidence of ground water contamination has been reported. Break down of imidacloprid is more rapid in soils with cover crops than in bare soils, taking between 48 and 190 days respectively.

In sunlight half the imidacloprid is expected to have degraded in approximately 39 days. In the absence of light breakdown of half the product may take as long as 229 days.

Breakdown in water

It takes 31 days or more for half of imidacloprid present in pH7 ground water to break down at 25°C. This breakdown is a faster in alkali water at the same temperature. Degree of leaching is dependent on the formulation of the imidacloprid. Wettable powders are worst, followed by soluble concentrates and suspension concentrates.

Non target effects

Imidacloprid appears to have low toxicity to fish based on laboratory assays using rainbow trout. However, one field based study indicated negative sub-lethal effects at low doses including increased stress and increased susceptibility to ecto-parasites.

Imidacloprid has very low toxicity to crustaceans and is moderately toxic to birds.

Imidacloprid is highly toxic to bees after either acute or chronic exposure and has been associated with colony collapse disorder. Significant adverse effects have been reported in other beneficial insects including carabid beetles, pirate bugs and ladybirds

Imidacloprid is a systemic insecticide and thus moves rapidly through plant tissues and may be present in detectable concentrations in leaves, pollen and vascular fluids.

Information sources

Fossen. 2006. Environmental fate of imidacloprid. Revised report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Gross. 2013. EU ban puts spotlight on complex effects of neonicotinoids. Current Biology 23(11):R462-R464

Lu, Warchol, Callahan.2012. In situ replication of honey bee colony collapse disorder. Bulletin of Insectology 65 (1): 99-106

Thiamethoxam

Breakdown in soil

In aerobic sandy loam soils, it is expected that half of the thiamethoxam will have broken down in 294-353 days. In silty loam soils, the speed of this break down is temperature dependent. At 20°C it is expected that half of the thiamethoxam will have broken down in 34-143 days, this process is slowed to 233 days at 10°C.

Breakdown in water

Thiamethoxam is likely to bind rapidly with soil sediments in water and is thus unlikely to remain bioavailable for prolonged periods. However, the compound is highly soluble, which suggests it is moderately likely to leach. In clear water half of the thiamoxam is likely to have degraded within 13 days.

Non target effects

Thiamethoxam has low toxicity to birds, very low toxicity to fish and is moderately toxic to crustaceans. There is a low potential for bioaccumulation. Thiamethoxam is highly toxic to bees after either acute or chronic exposure and has been associated with colony collapse disorder.

Thiamethoxam is a systemic insecticide and thus moves rapidly through plant tissues and may be present in detectable concentrations in leaves, pollen and vascular fluids.

Information sources

Henry, Begruin, Requier, Rollin, Odoux, Aupinel, Aptel, Tchamitchian, Decourtye. 2012. A common pesticide decreases foraging success and survival in honey bees. Science 336:348-350

Gross. 2013. EU ban puts spotlight on complex effects of neonicotinoids. Current Biology 23(11):R462-R464

Robinson. 2001. Evaluation of the new active Thiamethoxam in the product Cruiser 350 FS insecticide seed treatment. Report for National Registration Authority for Agricultural and Veterinary Chemicals

Synthetic pyrethroids

Detailed information about synthetic pyrethroids and their fate in the environment can be found in this publication, which is summarized below.

Synthetic pyrethroids are synthetic versions of the pyrethrins occurring in chrysanthemum flowers that paralyse insects’ nervous systems.

Originally pyrethroids were made to directly mimic pyrethrins (e.g. first generation pyrethroids including: bifenthrin, permethrin and d-phenothrin). However, some insects have developed resistance to these "first generation" pyrethroids. To combat this resistance, the compounds have been modified to be more potent, longer lasting and more effective at lower concentrations.

These second generation pyrethroids include: cypermethrin, cyfluthrin, deltamethrin, fenvalerate and lamda-cyhalothrin. There is now a third generation of synthetic pyrethroids, which include bifenthrin.

Permethrin

Among the most commonly used synthetic pyrethroids is permethrin. Permethrin is mainly broken down by soil microbes and by sunlight.

Breakdown in soil

In soil, microbes will take 40 days to break down half the permethrin. If there is no air in the soil it will take 197 days to break down half the permethrin. Absorption of permethrin into soil is rapid and strong, so there is almost no leaching and very little potential for runoff.

Breakdown in water

When there are no microbes in the water, it will take 110 days for half of the permethrin to be broken down. Permethrin is rapidly absorbed by aquatic soils, suggesting there is little time for organisms in the water to be exposed to the toxin. In sea water, sunlight will break down half the permethrin in approximately 14 days, but no significant reduction is observed after 14 days in shaded sea water. Microbes in marine sediments break permethrin down in less than 2.5 days.

Non-target effects

Permethrin is highly toxic to some fish and there is potential for accumulation of the toxin in fat, nervous tissue and in the liver and kidneys. Permethrin is also toxic to aquatic arthropods such as crabs and may also accumulate in their tissues. However, it should be noted that permethrin’s strong tendency to bind with soil and sediments reduces the organisms’ chances of exposure to the toxin in water.

On land permethrin is toxic to all insects including honey bees.

Permethrin has relatively low toxicity to mammals and birds. Some synthetic pyrethroids can have harmful effects on humans if they are breathed in, eaten or come into contact with skin. Symptoms of exposure may include allergic rashes, asthma-like breathing difficulty, headache, nausea, loss of coordination, tremors, convulsions and swelling. However, these symptoms typically pass quickly. Infants and people with pre-existing allergies or asthma are particularly susceptible to these sorts of reactions. It is therefore important to pay close attention to the SDS for each product.

Information sources

Imgrund. 2003. Environmental fate of permethrin. Report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Cypermethrin (2nd generation pyrethroid)

Breakdown in soil

Cypermethrin readily binds with soil surfaces. Sunlight is the major cause of degradation in this instance, with half of the originally quantity of the compound expected to have degraded in 8-16 days. Microbial breakdown in aerobic and anaerobic soils is comparable 6-20 days and less than 14 days respectively. Cypermethrin breaks down into a substance called PBA, which only breaks down further in aerobic conditions.

Breakdown in water

Cypermethrin has low solubility in water. Breakdown of half the cypermethrin in water is expected to take more than 50 days under normal environmental pH and temperature. Cypermethrin is also relatively resistant to breakdown by sunlight, with degradation to half the original quantity taking more the 100 days. However, cypermethrin has been noted to rapidly bind with organic particulates in water significantly and reducing bioavailability.

Non target effects

Cypermethrin has low toxicity to birds, but is highly toxic to fish and crustaceans. Cypermethrin binds with fat, indicating that at sub lethal doses the potential for bioaccumulation in fish and crustaceans is high.

Information sources

Jones. Undated. Environmental fate of cypermethrin. Report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Deltamethrin (2nd generation pyrethroid)

Breakdown in soil

Half of the deltamethrin is expected to have degraded within 11-72 days in aerobic soils. In anaerobic soils, degradation of half of the compound is expected to take between 31 and 36 days. Deltamethrin has low mobility in soil and tends to bind with soil organic matter, suggesting leaching is unlikely. However, the two products of deltamethrin degradation (Br2CA and PBA) are more mobile and may leach

Breakdown in water

Breakdown of deltamethrin in water is expected to take between 8-48 hours dependent on pH. Deltamethrin tends to bind with organic soil sediments in water within 48 hours, which limits its biological availability after this period.

Non target effects

Deltamethrin has moderate to high toxicity to fish under lab conditions. However, as deltamethrin binds rapidly with organic soil sediments it is expected to have low to very low toxicity to fish in field conditions under normal use, though bioaccumulation has been reported. Deltamethrin is highly toxic to crustaceans, but has been found to have low to very low toxicity to birds

Information sources

Extension Toxicology Network. 1995. Deltamethrin. Pesticide Information Profile

Anon. 2008. Deltamethrin. USA National Pesticide Information Centre technical fact sheet

Beta cyfluthrin (2nd generation pyrethroid)

Breakdown in soil

Beta cyfluthrin tends to bind with soils and is not expected to leach. In anaerobic loam soils half of the beta cyfluthrin can be expected to have degraded within approximately 34 days. Breakdown in aerobic (sandy loam) soils may be slower with half of the compound expected to be degraded within 63 days. This degradation is accelerated by sunlight which can break the compound down to half of its original volume in 2-16 days depending on temperature and soil pH.

Breakdown in water

Beta cyfluthrin is relatively insoluble in water, but tends to bind rapidly with organic soil sediments, limiting its availability to aquatic organisms. Beta cyfluthrin is comparatively stable in water and breakdown of half of the compound may be expected to take 193 days (at 25°C pH 7). Breakdown in water is accelerated in more alkali waters and by sunlight to 12.2 days (at 25°C pH 5).

Non target effects

Cyfluthrin is highly toxic to marine and freshwater fish and crustaceans. Cyfluthrin has low to very low toxicity to birds.

Information sources

Casjens. 2008. Environmental fate of cyfluthrin. Report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Extension Toxicology Network. 1995. Cyfluthrin. Pesticide Information Profile

Bifenthrin (3rd generation pyrethroid)

Breakdown in soil

Breakdown of bifenthrin in aerobic soils is dependent on soil composition and ranges between 97 days to 250 days for half the compound to have been degraded. Because bifenthrin binds with soil, it is unlikely to leach. Break down by sunlight on soil takes between 106 and 147 days.

Breakdown in water

Bifenthrin has low solubility in water and has been noted to rapidly bind with organic particulates in water, significantly reducing bioavailability. Bifenthrin was found to be stable in water at pH 5, 7 and 9 over a 30 day period. Break down in water by sunlight ranged between 276 and 416 days.

Non target effects

Bifenthrin is very highly toxic to fish and crustaceans and very high levels of bioaccumulation (~6000 x ambient persistence) have been observed in some fish. Bifenthrin has low toxicity to birds. However, given the potential for bioaccumulation in fish it is possible that some fish-eating birds may be adversely affected.

Information sources

Anon. 2011. Bifenthrin general fact sheet. USA National Pesticide Information Center technical fact sheet

Fecko. 1999. Environmental fate of bifenthrin. Report for Department of Pesticide Regulation California Environmental Protection Agency Environmental Monitoring Branch

Other neurotoxins

Other commonly used neurotoxins include avermectin and metaflumizone.

Abamectin

Bull, Ivie, MacConnell, Gruber, Ku, Arison, Stevenson, VandenHeuvel. 1984. Fate of Avermectin B1a [synonym of Abamectin] in Soil and Plants. Journal of Agricultural and Food Chemistry 32:94-102

EXTOXNET. 1994. Abamectin pesticide information profile prepared for Extension Toxicology Network (EXTOXNET), a pesticide information project of cooperative extension offices of Cornell University, Michigan State University, Oregon State University, and University of California at Davis

Metaflumizone

Australian Pesticides and Veterinary Medicines Authority. 2015. Evaluation of Metaflumizone in the Product SIESTA GRANULAR ANT BAIT. Public release summary for the Australian Pesticides and Veterinary Medicines Authority