Nosema sphingidis sp. n., a microsporidian parasite of the tobacco hornworm, Manduca sexta

Abstract

A microsporidian was isolated from a single field-collected larva of the tobacco hornworm, Manduca sexta, which was also parasitized by the hymenopterous parasite Apanteles congregatus. The pathogen is described as Nosema sphingidis sp. n., and an account is given of the general aspects of pathogenicity, symptomatology, and histopathology. The infection is initiated in the posterior portion of the midgut epithelium, and, as a result of a severe inflammatory response, the infection is limited largely to the adjacent tissues in the posterior portion of hornworm larvae. A series of cross-infectivity tests revealed that N. sphingidis was readily transmissible to a number of other lepidopterous insects, including five species of sphingids and the noctuid species Heliothis zea, Heliothis virescens, and Trichoplusia ni. Attempts to cross-infect larvae of M. sexta with several other species of Nosema (N. heliothidis, N. trichoplusiae, and N. acridophagus) were unsuccessful. A discussion is presented on the possibility that M. sexta is not the habitual host of N. sphingidis and that the natural infection observed was probably due to transmission during oviposition by the parasite A. congregatus.