Using SEM techniques, micromorphologica! features of the three larval instars of Wohlfahrtia nuba were studied, revealing their anterior ends, anterior spiracles, and posterior ends and posterior spiracles. We illustrated some important differences especially in shape and size of the mouth hooks, size, number and shape of the leaf-like structures surrounding the mouth vestibule and the blunt broad branches of the lower end of the frontal sclerites. Also, this work illustrates the process of first larval
moulting, which occurs through a longitudinal line starting from the anterior end of the larva till reaching its posterior end. Characteristic morphological differences were illustrated between the three larval instars as well.
Thus it seems that it is of much importance to use SEM in the study of the
larval stages of myiasis-producing flies and not only in the third stage.