Pyriproxyfen

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Pyriproxyfen is moderately volatile with a low water solubility but does not readily adsorb onto soil surfaces. Measured residue concentrations have been reported to decline by 50% in 24 hours in treated ponds. Pyriproxyfen adsorbs onto suspended organic matter and remains biologically activity for up to two months after an initial application. Its persistence in water in the absence of organic matter declines with increasing temperature and sunlight exposure.

Field studies conducted in California to evaluate the mobility and persistence of pyriproxyfen when applied to bare ground showed that both the parent compound and its major metabolites were found to be stable in soil for up to a year. The greatest pyriproxyfen concentrations were found in the 0-6 inch soil-layer. No pyriproxyfen residues were found above the level of quantitation below 12 inches. The half-life of pyriproxyfen in the 0-6 inch soil-layer was 36 days. No metabolite residues were found below 2 inches or greater than 120 days. The metabolism of ¹⁴C-Pyriproxyfen in a California sandy loam soil under aerobic conditions suggests that pyriproxyfen degrades rapidly via biological catalysis, having a half-life of 6.4 to 9.0 days and serving as a carbon source for soil microorganisms. The aerobic aquatic metabolic half-life of pyriproxyfen was 16.2 to 20.8 days. Metabolism in aerobic aquatic media proceeds through oxidative cleavage of the ester linkages. Pyriproxyfen degraded quickly under aerobic aquatic conditions (lake sediment and water) to two major metabolites (PYPAC and 4'-OH-Pyr), several minor intermediate metabolites, bound residues, and CO₂.

Crustaceans and aquatic insect larvae are sensitive to pyriproxyfen, although adverse effects were found to be reversible. Pyriproxyfen did not affect mayfly, dragonfly, ostracods, cladocerans, copepods, or beetles. Planktonic organisms showed no significant adverse effects resulting from 0.01 ppm. Pyriproxyfen produced LC50 values of 0.098 ppm against the estuarine shrimp L. tenuicornis, about 12 times the estimated field concentration. Against non-target terrestrial organisms, pyriproxyfen produced severe deformities at molt of several predatory bugs. Pyriproxyfen is, however, practically non-toxic to bees. Bumblebee colonies were found to develop normally after feeding on pyriproxyfen-sucrose solution.