INTERACTIONS OF THE INSECT GROWTH-REGULATOR PYRIPROXYFEN WITH IMMATURE AND ADULT STAGES OF THE STABLE FLY

Laboratory tests were conducted to evaluate the efficacy and posttreat ment fate of the insect growth regulator (IGR) pyriproxyfen after trea tment of different life stages of the stable fly, Stomoxys calcitrans L. Direct treatment of newly laid eggs with pyriproxyfen had no effect on hatch or subsequent development of larvae and pupae. When eggs wer e placed on larval rearing medium treated with different concentration s of the IGR there was a strong reduction in the yields of F1 adults c ompared with untreated controls; probit regressions of data indicated the concentration of the IGR needed for a 50% reduction in adult emerg ence (IC50) was 12.8 parts per billion (ppb). Direct treatment of thir d instars by immersing them for 1 min in aqueous solutions of pyriprox yfen also caused a strong reduction in yields of F1 adults (IC50 of 2. 6 ppb). Exposure of mixed sexes of adults to different residual concen trations of pyriproxyfen resulted in significant dose-dependent reduct ions in yields of F1 pupae. Although there also appeared to be reducti ons in the subsequent emergence of adults from those pupae, the data w ere too variable to show a reliable concentration-response relationshi p. Studies of the posttreatment distribution and fate of topically app lied [C-14]pyriproxyfen in adult stable fly females indicated the IGR penetrated the cuticle very rapidly (>90% after 8 h) and then was meta bolized and excreted at a very slow rate. Because pyriproxyfen has goo d stability in the environment, and is highly active against larval st ages of the stable fly, its use as a treatment of breeding sites could have good potential as a tactic to aid in managing field populations of the pest.