Life cycle of Amblyospora indicola (Microspora: Amblyosporidae), a parasite of the mosquito Culex sitiens and of Apocyclops sp. copepods

Abstract The life cycle of Amblyospora indicola , a parasite of the mosquito Culex sitiens , was revealed by field observations and laboratory infection experiments conducted in Australia. In northern Queensland, infected C. sitiens larvae were often found breeding in association with two cyclopoid copepods: Apocyclops dengizicus and an undescribed species of the same genus. The latter species was found to be an intermediate copepod host of this microsporidium whereas A. dengizicus was not. One complete cycle of the parasite extends over two mosquito generations (by transovarial transmission from females with binucleate spores to their eggs) and by horizontal transmission between mosquitoes and copepods. The latter involves horizontal transmission from mosquitoes to copepods via meiospores produced in larval fat body infections and horizontal transmission from copepods to mosquitoes via uninucleate spores produced within infected copepods. Uninucleate clavate spores were formed in Apocyclops sp. nov. copepods 7–10 days after exposure to larval meiospores and were infectious to larvae of a microsporidian-free colony of C. sitiens . The development of A. indicola within mosquito larvae exposed to infected copepods is similar to that of A. dyxenoides infecting C. annulirostris . It proceeds from stages with a single nucleus to diplokaryotic binucleate cells in oenocytes. These stages persist through pupation to adult emergence after which time a proportion of male mosquitoes and female mosquitoes may develop binucleate spores without the need for a blood meal. A proportion of both male and female larval progeny of infected females with binucleate spores develop patent fat body infections via transovarial transmission and die in the fourth larval instar. Oenocytic infections were not observed in any survivors of patently infected larval batches in which some individuals developed fat body infections. This implies that transovarial transmission only takes place for one mosquito generation after exposure to copepods and that there is an obligate alternation between mosquitoes and copepods during each cycle of the parasite. It is considered that A. pinensis , described by Kettle and Piper (1988, Eur. J. Protistol. , 23 , 229–241), infecting C. sitiens in Australia, is not a valid species and that it is a synonym of A. indicola .