Development of Dirofilaria scapiceps (Leidy, 1886) (Nematoda: Filarioidea) in Aedes spp. and Mansonia perturbans (Walker) and responses of mosquitoes to infection

Abstract

Dirofilaria scapiceps (Leidy, 1886) developped in the abdominal fat body of Aedes canadensis, A. euedes, A. excrucians, A. provocans, A. punctor, A. stimulans/fitchii, A. vexans, and Mansonia perturbans which occur in enzootic areas in Ontario. Abundances of third-stage larvae were greatest in A. euedes and A. excrucians. Transmission took place in July and August. Development also occurred in Aedes aegypti (Liverpool strain) but not in A. triseriatus and A. trivittatus. Larvae in A. euedes and A. excrucians developed within syncytia containing hypertrophied adipocyte nuclei; third-stage larvae were first observed at 10 days postinfection (26 °C) and all larvae invariably developed to the third stage. Syncytia containing hypertrophied adipocyte nuclei apparently act as a nutrient source and may be essential for normal development of larvae. In A. stimulans/fitchii, syncytia did not form or formed abnormally, a longer period (12 days) was required for development to the third stage, and many larvae failed to reach the third stage. Many developing larvae in A. aegypti were surrounded by syncytia but adipocyte nuclei in them were not hypertrophied. Larvae in A. aegypti given one blood meal commonly did not reach the third-stage, although development proceeded normally in A. aegypti given two blood meals. Third-stage larvae have postdeirids, two terminal caudal papillae, and a terminal caudal cuticular cap and are readily distinguished from third-stage larvae of other Dirofilaria species. Male third-stage D. scapiceps possess spicular pouch primordia, previously unreported in infective filarioid larvae.