LOPEZ, E.M.*; NORRIS, D.O.: The Actions of Methoprene Acid on a Developing Urodele

The objective of this study was to characterize the biological actions of methoprene acid (MA), a natural degradation product of the insecticide, methoprene, on a developing axolotl, Ambystoma mexicanum, and to assess the levels of developmental stability following treatment of embryos and hatchlings. We tested the null hypotheses that (1) technical grade MA would produce no developmental malformations similar to those produced by the positive control, retinoic acid (RA) and (2) the degree of vulnerability to the actions of MA would not differ in exposed embryos versus hatchlings. Animals were exposed to 1 of 4 concentrations of MA (0, 30, 150, and 300 ug/L), or to 1 of 4 concentrations of RA (0, 0.3, 1.5, 3.0 ug/L), depending on the treatment group to which they were assigned. In addition, half of the subjects were treated from blastula stage to hatching only, while the second half were treated beginning at hatching for the duration of the experiment. All animals were grown out until full hindlimb development, at which time the experiment was terminated. Developmental stability was determined by measuring fluctuating asymmetry of the hindlimbs, forelimbs, and eyes within individuals. Malformations of the head, eyes, limbs, and toes that were previously characterized by other studies as retinoid-like were seen in both MA- and RA -treated animals. Effects on developmental stability were consistently observed as fluctuating asymmetry of the forelimbs and hindlimbs in MA- and RA -treated animals.