EFFECT AND FATE OF THE INSECT GROWTH-REGULATOR PYRIPROXYFEN AFTER APPLICATION TO THE HORN FLY (DIPTERA, MUSCIDAE)

Laboratory studies demonstrated that the insect growth regulator (IGR) pyriproxyfen effectively inhibits development of the horn fly, Haemot obia irritans (L.). The primary IGR response elicited by pyriproxyfen- suppression of the emergence of F1 adult progeny of treated parents-is similar to that observed in comparable studies of horn flies and othe r dipterans treated with juvenile hormone analogues. Pyriproxyfen is e ffective when adult females are treated topically (LC50 = 0.96 mug per insect), adults of mixed sexes are exposed to residues on glass (LC50 = 12.83 mug/cm2), and the IGR is incorporated with the larval rearing medium (LC50 = 9.3 ppb); it was ineffective as a direct application t o eggs. Timing of treatment of adults is an important factor in their response to pyriproxyfen. Adult females are most susceptible to topica l applications on the second day after emergence; their response to re sidues on glass is minimum the first day after emergence and then incr eases significantly each day as the time of exposure increases over a 4-d period. Studies of the fate of topically applied [C-14]pyriproxyfe n in adult females demonstrated that cuticular penetration is extremel y rapid (almost-equal-to 95% in 8 h), and that relatively large propor tions of the applied concentration accumulate internally because of sl ow metabolism and excretion.