METHOPRENE

Description

Methoprene is the common name for a racemic mixture of two enantiomers (R and S in a ratio of 1:1). The activity of the compound as a juvenile hormone (JH) mimic is restricted to the S enantiomer. Methoprene was the first insect growth regulator approved in the 1970s by the US Environmental Protection Agency after extensive studies showing low toxicity to vertebrates and rapid natural chemical degradation in the environment and through organism metabolism. Nowadays, it is one of the most widely used and successful insect growth regulators. Different products containing methoprene (e.g., pesticides, veterinary drugs) are commercially available in different forms (emulsifiable concentrates, granules, pellets, briquettes, aerosols, or sustained-release formulations). Some of these are applied to water for mosquito control whereas others are sprayed in areas where foods are stored to prevent insect infestations. Methoprene may be used in combination with other active insecticides to optimize pest control.

Chemical properties

Amber colored liquid. Faint fruity odor.

The Uses of METHOPRENE

Methoprene controls many insect pests (Diptera, Pharaoh’s ants, and also Coleoptera, Homoptera and Siphonaptera) in public health, stored commodities, food handling, processing and storage establishments, mushroom houses, on animals and on plants (including glasshouse plants).

The Uses of METHOPRENE

ectoparasiticide

The Uses of METHOPRENE

Methoprene is a broad-spectrum synthetic JH mimic, which acts as an insect growth regulator (insecticide). It prevents larval insect stages from undergoing metamorphosis to viable adults and thus acts as a larvicide. Methoprene is considered a biochemical pesticide because rather than controlling target pests through direct toxicity, methoprene interferes with the insect life cycle, preventing the insect from reaching maturity or reproducing.
It is useful for control of a variety of insect pests including ants, mosquitoes, flies, fleas, beetles, lice, and moths, but is only effective against larvae, not adults or pupae. In order to control some of these insects, methoprene is used in the production of a number of foods including meat, milk, mushrooms, peanuts, rice, and cereals. Many different products (e.g., pesticides, veterinary drugs) and formulations containing methoprene are commercially available. Methoprene products used for protecting pets such as cats and dogs include capsules administered orally and flea collars used externally. Production animals (e.g., cattle) typically receive methoprene in the diet as a food additive. Other formulations of methoprene include emulsifiable concentrates, pellets and tablets, granules, and aerosols. Some of these are applied to water for mosquito control whereas others are sprayed in areas where foods are stored to prevent insect infestations. A potential therapeutic use of methoprene was proposed in the context of African sleeping sickness, since it was observed that this compound killed Trypanosoma brucei in culture. However, methoprene acid, resulting from the insecticide metabolism, exhibited no efficiency as trypanocide. Consistently, methoprene administered to infected mice showed to be unable to eliminate trypanosomes from the blood.

Definition

An insecticidal preparation said to act in the manner of a juvenile hormone, which arrests development of insects in the larval stage.

Agricultural Uses

Insect growth hormone: Methoprene is an insect growth regulator (IGR) used against a variety of insects including horn flies, mosquitoes, beetles, tobacco moths, sciarid flies, fleas (eggs and larvae), fire ants, pharoah ants, midge flies and Indian meal moths. Controlling some of these insects, methoprene is used in the production of a number of foods including meat, milk, mushrooms, peanuts, rice and cereals. It also has several uses on domestic animals (pets) for controlling fleas and to control insects in wastewater, sludge beds and ponds. For oral use in dogs, 9 weeks of age and older and 4 pounds body weight or greater, for the prevention and control of flea populations [21 CFR 520.1390]. Not approved for use in EU countries . Registered for use in the U.S.

Trade name

ALTOSID®; APEX®; DIACON®; DIANEX®; ENT 70,460®; EXTINGUISH®; FLEATROL®; KABAT®; MANTA®; MOORMAN’S® IGR CATTLE CONCENTRATE; OVITROL®; PHARORID®; PRECOR®; ZR-515®

Potential Exposure

Methoprene is a natural insect growth regulator (IGR) that mimics juvenile hormone(s) and is used against a variety of insects including horn flies, mosquitoes, beetles, tobacco moths, sciarid flies, fleas (eggs and larvae), fire ants, pharoah ants, midge flies and Indian meal moths. Controlling some of these insects, methoprene is used in the production of a number of foods including meat, milk, mushrooms, peanuts, rice and cereals. It also has several uses on domestic animals (pets) for controlling fleas and to control insects in wastewater, sludge beds and ponds. For oral use in dogs, 9 weeks of age and older and 4 lb body weight or greater, for the prevention and control of flea populations

Environmental Fate

Methoprene may be degraded by demethylation, hydrolysis, oxidative cleavage, and photodegradation, resulting in the formation of a series of metabolites that include methoprene acid and citronellic acid. The primary modes of degradation are photodegradation and degradation by aquatic microorganisms.
It is metabolized rapidly in soil under both aerobic and anaerobic conditions (half-life = 10–14 days). The major microbial degradation product is carbon dioxide. Degradation in both freshwater and saltwater is also quite rapid with a halflife of 10–35 days at 20 ℃. Methoprene is not very soluble in water (<2 ppm) and as a result is not highly mobile in soil. Because of this and its rapid biodegradation, methoprene does not persist for long periods in soil and is unlikely to contaminate groundwater. When released into water, methoprene is expected to adsorb to suspended solids and sediment. A high potential for bioconcentration in aquatic organisms has been suggested, with an estimated bioconcentration factor of 3400. However, studies with bluegill sunfish, showed no significant bioconcentration of methoprene in fish tissues as a result of aquatic exposure.
Methoprene rapidly degrades in plants, with a half-life of 1–2 days in alfalfa when applied at a rate of 1 pound per acre. In rice, the half-life is less than 1 day. In wheat, its half-life was reported to be 3–7 weeks, depending on the level of moisture in the plant.

Metabolic pathway

Methoprene is readily degraded biologically by hydrolysis of the ester group, O-demethylation and oxidative cleavage of the bond at the 4-position.

Shipping

UN3082 Environmentally hazardous substances, liquid, n.o.s., Hazard class: 9; Labels: 9-Miscellaneous hazardous material, Technical Name Required

Degradation

Methoprene (1) is stable in water and in the presence of aqueous acids and alkalis. It is sensitive to UV light. Isomerisation of the double bond is facile. In sunlight (S)-methoprene decomposes to a number of products. These include trans,trans-( S)-methoprenic acid, 2-cis,4-trans-( S)-methoprenic acid, and 2-cis,4-trans-(S)-methoprene.
When [5-¹⁴C]methoprene was irradiated in direct sunlight in Pyrex vessels in aqueous solutions (0.01 ppm and 0.50 ppm) the DT₅₀ was less than one day. Initially decomposition was rapid, but after one week 12% and 5% 1 remained in the 0.5 and 0.01 ppm solutions, respectively. Carbon dioxide was collected and total ¹⁴C recovered was not less than 94% during a 21-day experiment. Five products were characterised as oxygenated products but could not be positively identified. For product identification, an aqueous emulsion of methoprene was irradiated in sunlight and four photoproducts (24% yield) were characterised as methoxycitronellal dimethyl acetal(3,3.9%), methoxycitronellic acid (4,4.7%), an epoxide of methoprene (5,4%) and a methyl ketone (6,4%). In addition to unreacted methoprene there were at least 46 other photoproducts of which none represented more than 2% yield. Rose Bengal and anthraquinone increased the rate of photocatalysed breakdown of methoprene and the profile of products was similar to that obtained by irradiation of a thin film. The extent of decomposition in the presence of anthraquinone was 86% after 6 hours and the predominant product was methoxycitronellal (2, l0^-14%). Photosensitised oxidation was slow and 47% of the original was unreacted and a single major product (12%) was identified as the dihydrofuranol (7) (Quistad et al., 1975a) (see Scheme 1).

Toxicity evaluation

Acute oral LD₅₀ for rats: >34,600 mg/kg

Waste Disposal

It is the responsibility of chemical waste generators to determine if a discarded chemical is classified as a hazardous waste. See 40 CFR Parts 261.3 for United States Environmental Protection Agency guidelines for the classification determination. In addition, in order to ensure complete and accurate classification, waste generators must consult state and local hazardous waste regulations. Incineration might be an effective disposal procedure where permitted. If an efficient incinerator is not available, the product should be mixed with large amounts of combustible material and contact with the smoke should be avoided. In accordance with 40CFR165, follow recommendations for the disposal of pesticides and pesticide containers