Distribution of third-stage Dirofilaria roemeri (Nematoda: Filarioidea) in the tissues of tabanidae (Diptera)

Third-stage Dirofilaria roemeri larvae were detected in 2 Dasybasis oculata and one Tabanus parvicallosus collected in Queensland, Australia. The larvae had invaded the brain, eye, nerve cord, muscles of the mouthparts, horizontal and indirect flight muscles, fat body, hind gut and gonad and produced discernible injury in the eye, nerve cord and musculature. 3rd-stage Dirofilaria roemeri migrate from the abdomen via the haemocoelic spaces of the thorax to the head. Although the emergence of infective forms from the head was not observed, the numbers and orientation of larvae in the lumen of the labrum, and their absence from the labio-hypopharyngeal membrane suggest that they escape by rupturing either the tip of the labrum or, more likely,, the delicate labro-epipharyngeal membranes binding the anterior and posterior blades of this element. There was no evidence that D. roemeri had a truly detrimental effect on the tabanids and the hosts showed no response to the presence of the filarioids.