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, Haemotobia 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 other dipterans treated with juvenile hormone analogues. Pyriproxyfen is effective 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 to eggs. Timing of treatment of adults is an important factor in their response to pyriproxyfen. Adult females are most susceptible to topical applications on the second day after emergence; their response to residues on glass is minimum the first day after emergence and then increases significantly each day as the time of exposure increases over a 4-d period. Studies of the fate of topically applied [C-14]pyriproxyfen in adult females demonstrated that cuticular penetration is extremely rapid (almost-equal-to 95% in 8 h), and that relatively large proportions of the applied concentration accumulate internally because of slow metabolism and excretion.