Parasitic development of the mermithid nematode Reesimermis nielseni in the larval mosquito Aedes aegypti

Newly hatched Aedes aegypti larvae were experimentally infected with controlled levels of infection of the mermithid nematode Reesimermis nielseni and the development of the parasite was recorded. The nematode increased in length by 18-fold and in width by 16-fold during a relatively short 6- to 8-day parasitic phase. Most of the nematode's growth was restricted to the latter half (3 days) of the infective period. A cuticularized tube, extending posteriorly from the stoma, was present throughout parasitic development. After 3 days infection, the nematode possessed a membrane-bound stichosome containing 16 stichocytes, and a cellular trophosome with storage nutrient granules beginning to accumulate in the intercellular spaces. Between 3 and 4 days infection, the parasite probably molted as its growth rate suddenly increased, its stylet was lost, and a caudal appendage acquired. The stichosome, trophosome, and genital rudiment continued to develop for the rest of the infective period. A discrete granular body of unknown function and containing a large nucleated cell developed anterior to the stichosome. By the 5th and 6th days of infection, the enlarged trophosome, packed with storage globules, almost completely obscured the stichosome and genital rudiment. The nematode does not possess a stylet to facilitate emergence from its host, nor does it appear to molt immediately before emergence. The possible functions of the stichosome and cuticularized tube are discussed.