The larvicidal activity of the juvenile hormone mimic pyriproxyfen was evaluated against the 4th larval instar of Culex pipiens under 5 constant temperatures in the laboratory. Toxicity of this insect compound increased with temperature. The 50% lethal concentrations ranged between 0.00111 ppm at 20 degrees C and 0.00013 ppm at 32 degrees C. A similar trend was observed for the 90% lethal concentrations, which varied from 0.00379 ppm to 0.00024 ppm at the 2 temperatures, respectively. Some effects of the compound were observed on the ultrastructure of the 4th-stage larval integument, where electron micrographs revealed the destruction of procuticle lamellae, formation of cuticular vacuoles, deformed mitochondria, and destruction of nuclear envelopes and the epidermal layer, in addition to an increase in electron-dense lysosomelike bodies.
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