SCANNING ELECTRON-MICROSCOPY STUDY OF EST RUS-OVIS (LINNE 1761) LARVAE

Scanning electron microscopy of the three larval instars of (Estrus ov is, the sheep nasal bot fly, allowed the study of spines and hooks. Th e first instar larva have many strong spines and hooks to keep on muco sa and to resist to the air stream in nasal cavities. The second insta r shows only weak spinulosity ; it lives in a quiet place : middle mea tus or sinuses, The third instar larva carries ventral spines to move out of the upper respiratory tract. All these structures show a very g ood adaptation to the larval environment. A ventral orbicular hole wit h prominent rims is also described on the first larval instar, its sig nificance is not known.