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Methoprene is commonly added to insecticides to be used against insects. It comes in two different forms called s-methoprene and r-methoprene, and s-methoprene is the one that behaves like an important hormone in insects. It can be used against fleas, flies, moths, beetles, and other insects. Methoprene was first registered for use in the United States in 1975 and s-methoprene was later registered in 1985.

Methoprene is an insect growth regulator. By acting like an insect hormone, it interferes with insect growth and development. It can prevent normal molting, egg-laying, egg-hatching, and development from the immature phase (i.e. caterpillar) to the adult phase (i.e. moth). This prevents the insects from reproducing.

Methoprene can cause slight irritation if it gets into a person’s eyes or lungs. If you touch it, methoprene can cause mild or moderate skin irritation. However, in several studies where methoprene was applied to the skin of laboratory animals, no effects or irritation were noted.

In one study with very high doses (10 g/kg), dogs that were fed methoprene showed signs like vomiting, dilated pupils, changes in behavior, breathing, and body movements. When researchers cut the dose in half (5 g/kg), the dogs had no observable signs or symptoms

Methoprene is moderately toxic to some fish and low in toxicity to others. Methoprene can accumulate in fish tissues. It is slightly toxic to crustaceans such as shrimp and crayfish, and very highly toxic to freshwater invertebrates.

Methoprene is relatively non-toxic to birds. It also appears to be low in toxicity to adult bees, although bee larvae may be more sensitive.

Read more: Insecticides