If ingested, pyriproxyfen can irritate or burn the esophagus and gastrointestinal tract. Moreover, pyriproxyfen is partially absorbed by the gut, and may be stored in fat deposits and breast milk.

As a respiratory irritant, inhaling pyriproxyfen can result in dizziness, headaches, weakness, and nausea. In severe cases, acute lung injury may occur.

This chemical is believed to be a potential endocrine disruptor, and has been shown to have an estrogenic effect.

Upon exposure to elevated temperatures, pyriproxyfen will decompose and emit toxic fumes that contain carbon monoxide and nitrogen oxides.

Pyriproxyfen is very toxic to aquatic life and may leave long-lasting effects on water-based plants and animals. Ergo, it shouldn’t be used near bodies of water or allowed to seep into water sources. 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. So a blanket approach of spraying and contaminating all the environment seems totally ridiculous to start of with.