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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Methoprene

Trade and Other Names: Trade names include Altosid, Apex, Diacan, Dianex, Kabat, Minex, Pharorid, Precor, and ZR-515.

Regulatory Status: Methoprene is a slightly to practically nontoxic compound in EPA toxicity class IV. It is a General Use Pesticide (GUP). Labels for containers of products containing methoprene must bear the Signal Word CAUTION.

Chemical Class: Not Available

Introduction: Methoprene is a compound which mimics the action of an insect growth regulation hormone. It is used as an insecticide because it interferes with the normal maturation process. In a normal life cycle, an insect goes from egg to larva, to pupa, and eventually to adult. Methoprene artifically stunts the insects' development, making it impossible for insects to mature to the adult stages, and thus preventing them from reproducing.

To be effective, it is essential that this growth inhibitor be administered at the proper stage of the target pest's life cycle. Methoprene is not toxic to the pupal or adult stages. Treated larvae will pupate but adults do not hatch from the pupal stage. Methoprene is also considered a larvicide since it is effective in controlling the larval stage of insects. Methoprene is used in the production of a number of foods including meat, milk, eggs, mushrooms, peanuts, rice, and cereals. It is also used in aquatic areas to control mosquitoes and several types of ants, flies, lice, moths, beetles, and fleas. It is available in suspension, emulsifiable and soluble concentrate formulations, as well as in briquette, aerosol, and bait form.

Formulation: It is available in suspension, emulsifiable and soluble concentrate formulations, as well as in briquette, aerosol and bait form.

Toxicological Effects:

• Acute toxicity: Methoprene is practically nontoxic when ingested or inhaled and slightly toxic by dermal absorption. The oral LD50 for methoprene in rats is greater than 34,600 mg/kg, and in dogs is greater than 5000 mg/kg [1]. It is slightly toxic by skin exposure, with reported dermal LD50 values of greater than 2000 to 3000 mg/kg in rabbits [1]. Methoprene is not an eye or skin irritant, and it is not a skin sensitizer [1]. The inhalation LC50 for methoprene in rats is greater than 210 mg/L [155]. No overt signs of poisoning have been reported in incidents involving accidental human exposure to methoprene [155].
• Chronic toxicity: No methoprene-related effects were observed in 2-year feeding trials with rats given doses of 250 mg/kg/day, nor in mice given 30 mg/kg/day [1]. Liver changes were observed in mice fed 50 to 250 mg/kg/day of methoprene during an 18-month study [155]. Increased liver weights occurred in rats fed 250 mg/kg/day for 90 days, but not during a 24-month feeding study in which rats were fed 125 mg/kg/day [155].
• Reproductive effects: Experimental data indicate that no reproductive hazards are associated with methoprene [155]. No methoprene-related effects were observed in three-generation reproduction studies in rats receiving dietary doses of 125 mg/kg/day [1].
• Teratogenic effects: There have been no teratogenic effects in animals dosed with methoprene; teratogenic effects were not seen in rats at doses of about 25 mg/kg/day, or in rabbits at doses of about 15 mg/kg/day [156,157]. Methoprene does not appear to be teratogenic.
• Mutagenic effects: Methoprene does not appear to be mutagenic. No methoprene-related mutagenic effects were observed in rats following a single dose of 2000 mg/kg [158].
• Carcinogenic effects: No tumors were seen in an 18-month feeding study with mice, or in a 24-month oncogenicity study with rats [156]. These data suggest that methoprene is not carcinogenic.
• Organ toxicity: The target organ primarily affected by methoprene after long-term exposure is the liver.
• Fate in humans and animals: In mammals, methoprene is rapidly and completely broken down and excreted, mostly in the urine and feces [157]. Some evidence suggests that methoprene metabolites are incorporated into natural body components [155]. Methoprene is excreted unchanged in cattle feces in amounts that are sufficient to kill some larvae that breed in dung [131].

Ecological Effects:

• Effects on birds: Methoprene is slightly toxic to birds [1,158]. The reported 5- to 8-day LC50 values for Altosid, a methoprene formulation, are greater than 10,000 ppm in mallard ducks and bobwhite quail, and the acute oral LD50 for Altosid is greater than 4640 ppm in chickens [1,158]. In mallards an acute oral LD50 of greater than 2000 mg/kg was determined [158]. Nonlethal effects that may affect survival of the birds did appear at acute oral doses of 500 mg/kg. These effects appeared as soon as 2 hours after treatment and persisted for up to 2 days and included slowness, reluctance to move, sitting, withdrawal, and incoordination [63]. These effects may decrease bird survival by making them temporarily more susceptible to predation. No effects were observed in the reproduction of bobwhite quail and mallard ducks at 30 ppm constant feeding of Altosid [158].
• Effects on aquatic organisms: Methoprene is slightly to moderately toxic to fish [157]. The reported 96-hour LC50 values for the methoprene formulation Altosid were 4.6 mg/L in bluegill sunfish, 4.4 mg/L in trout, and greater than 100 mg/L in channel catfish and largemouth bass [1,8]. Methoprene residues may have a slight potential for bioconcentration in bluegill sunfish and crayfish [155]. Methoprene is very highly toxic to some species of freshwater, estuarine, and marine invertebrates, while the acute LC50 values are greater than 100 mg/L in freshwater shrimp, and it is greater than 0.1 mg/L in estuarine mud crabs [159]. Altosid had very little effect, if any, on exposed non-target aquatic organisms including waterfleas, damselflies, snails, tadpoles, and mosquito fish [159].
• Effects on other organisms: Tests with earthworms showed little if any toxic effects on contact [159]. It is nontoxic to bees [1].

Environmental Fate:

• Breakdown in soil and groundwater: Methoprene is of low persistence in the soil environment; reported field half-lives are up to 10 days [155]. In sandy loam, its half-life was calculated to be about 10 days [155]. When Altosid was applied at an extremely high application rate of 1 pound per acre, its half-life was less than 10 days [155]. In soil, microbial degradation is rapid and appears to be the major route of its disappearance from soil [155,157]. Methoprene also readily undergoes degradation by sunlight [157]. Methoprene is rapidly and tightly sorbed to most soils [155]. It is slightly soluble in water [1]. These properties, along with its low environmental persistence make it unlikely to be significantly mobile. In field leaching studies, it was observed only in the top few inches of the soil, even after repeated washings with water [155,159].
• Breakdown in water: Methoprene degrades rapidly in water [8]. Studies have demonstrated half-lives in pond water of about 30 and 40 hours at initial concentrations of 0.001 mg/L and 0.01 mg/L, respectively [49]. At normal temperatures and levels of sunlight, technical Altosid is rapidly degraded, mainly by aquatic microorganisms and sunlight [159,49].
• Breakdown in vegetation: Altosid is biodegradable and nonpersistent, even in plants treated at very high rates. It has a half-life of less than 2 days in alfalfa when applied at a rate of 1 pound per acre [159]. In rice, the half-life is less than 1 day [49]. In wheat, its half-life was estimated to be 3 to 7 weeks, depending on the level of moisture in the plant [155]. Plants grown in treated soil are not expected to contain methoprene residues.

Physical Properties:

• Appearance: Technical methoprene is a amber or pale yellow liquid with a faint fruity odor [1]
• Chemical Name: ispropyl(E,E)-(R,S)-11-methoxy-3,7,11-trimethyldodeca-2,4-dienoate [1]
• CAS Number: 40596-69-8
• Molecular Weight: 310.48
• Water Solubility: 1.4 mg/L @ 25 C [1]
• Solubility in Other Solvents: Miscible in organic solvents [1]
• Melting Point: Not Available
• Vapor Pressure: 3.15 mPa @ 25 C [1]
• Partition Coefficient: Not Available
• Adsorption Coefficient: Not Available

Exposure Guidelines:

• ADI: 0.1 mg/kg/day [12]
• MCL: Not Available
• RfD: Not Available
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Zoecon Corp.
12005 Ford Rd., Suite 800
Dallas, TX 75234

• Phone: Not Available
• Emergency: 708-699-1616
  

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.