Adaptations to Endoparasitism in the Larval Integument and Respiratory System of the Flea Uropsylla-Tasmanica Rothschild (Siphonaptera, Pygiopsyllidae)

Abstract

An histological study of flea larvae was carried out in order to compare free-living larvae with the unique endoparasitic larva of Uropsylla tasmanica, a species found on marsupial cats in Tasmania and Victoria, Australia. The free-living species examined were the cat flea Ctenocephalides felis, and Odontopsyllus quirosi. Body shape in U. tasmanica is adapted to endoparasitism; the anterior segments are greatly expanded and the abdominal segments are reduced from ten to eight. This reduction brings the last abdominal spiracle (8), to the posterior end of the larva, allowing better access to oxygen from the atmosphere. Possible evolutionary steps in this modification are suggested. Third-instar U. tasmanica have non-functional prothoracic spiracles and the metathoracic spiracles are either non-functional or absent. All three instars of C. felis are peripneustic, and third-instar O. quirosi larvae are holopneustic. Contrary to previous ideas, the respiratory systems of flea larvae do not provide exceptions to the generalisations that in holometabolous insect larvae the metathoracic spiracle is nearly always non-functional, and, that functional and non-functional spiracles coexist in these larvae. Features in U. tasmanica convergent with those of endoparasitic, saprophagous and aquatic fly larvae are discussed.