RESUMEN
Scanning electron microscopy (SEM) was used to study the morphological alteration occurring in Habronema muscae adult female worms after in vitro exposure to different doses of Verbesina alternifolia oil extract. The half maximal lethal concentration (LC50) was reached 400 ppm after 24hrs, while LC100 was reached 600 ppm after 48hrs. Irreversible degenerative changes were recorded such as shrinking, detachment and distortion of the cuticle, cephalic and distal region. The cuticular surface had a wrinkled, corrugated appearance with longitudinal ridges and transverse thick folds. The lips and papillae were deformed and aggregated over each other. There is a direct relation between the level of the recorded degenerative changes and the increase in the dose and exposure time. In the same time no degen'erative changes were recorded in the control worm exposed to PBS till the end of the exposure period.