Pyriproxyfen is a new insect growth regulator,vith potent activity aga
inst developing stages of the cat flea, Ctenocephalides felis. To dete
rmine its duration of action after application as a spot-on topical tr
eatment, 20 cats were allocated to two groups, One group acted as untr
eated controls, and each cat in the other was given a single dose of 1
mg/kg pyriproxyfen. Each cat was infected with fleas at weekly interv
als and caged. Eggs were collected and their viability determined as a
measure of the effect of the agent on adult fleas. The effect of the
transfer of pyriproxyfen from each; cat to its immediate surroundings
was monitored by observing the development of fertile flea eggs placed
on samples of blanket taken from each cage, Results from untreated co
ntrol cats showed that the experimental conditions were favourable for
the lifecycle of the nea. Flea reproduction on treated cats was inhib
ited completely for seven weeks and substantially for at least a furth
er two weeks, Blankets used by cats treated up to two weeks previously
prevented flea development entirely and substantial control was still
achieved up to four weeks after treatment.