Comparative scanning electron microscopy of Gasterophilus third instars.

Comparison of cuticular features, including spine distribution and shape, structure of the maxillae and mandibles, the cephalic sensillae and the terminal abdominal segments of third instar Gasterophilus haemorrhoidalis, Gasterophilus inermis, Gasterophilus intestinalis, Gasterophilus meridionalis, Gasterophilus nasalis and Gasterophilus pecorum was conducted using scanning electron microscopy. One or more features distinguished among the species, with the exception of G. haemorrhoidalis and G. intestinalis, which shared all morphological characteristics. The features presented in this study complement and extend those presented in Zumpt's compendium. The function of some features described by Zumpt (e.g. the 'warts' on the rim of the respiratory chamber) is clarified and the presence of previously described sensory structures in the grooves on the maxillae of G. intestinalis is called into question.