Effect of temperature and the synergist piperonyl butoxide on imidacloprid toxicity to the cat flea (Siphonaptera: Pulicidae)

The toxicity of imidacloprid to cat fleas on glass was investigated at 20, 26, 30, and 35 degrees C. Imidacloprid was most toxic to adult cat fleas at 35 degrees C and to larvae at 20 degrees C. Piperonyl butoxide (PBO), a synergist, increased the relative potency of imidacloprid (1:5 imidacloprid:PBO) 16-fold at 26 degrees C against adults, but had no effect at 35 degrees C. No synergism occurred in larvae at 20 degrees C, but addition of PBO (1:5 imidacloprid:PBO) doubled toxicity at 26 degrees C. PBO (1:5 imidacloprid:PBO) could possibly be used to synergize imidacloprid premise treatments (20-30 degrees C), but it is not likely to be effective in pet treatments because no synergism occurred in adult fleas at 35 degrees C (average fur temperature of tested cats and dogs).