A new Helicosporidium spp. isolate recently purified from an aquatic weevil, Cyrtobagus salviniae Calder & Sands, was capable of infecting and reproducing in three heterologous noctuid hosts. Regardless of host species, oral treatment of Heliocoverpa zea (Boddie), Spodoptera exigua (Hübner), or Trichoplusia ni (Hübner) early instars with cyst preparations of Helicosporidium spp. resulted in ≈50% infection of the challenged larvae. The sex ratio did not differ between infected and control groups, suggesting the existence of a natural, nonsex-related resistance to the disease. Injection of Helicosporidium spp. into the hemocoels of late instars resulted in virtually 100% infection, indicating that resistance is related to the ingestion of the pathogen and therefore affiliated with midgut-mediated barriers. The pathogen’s development was not interrupted by metamorphosis; likewise, the infection did not necessarily interrupt the insects’ development. When treated as early instars, 50–90% of the infected larvae formed pupae, of which 20–30% emerged as adults. However, a high proportion of the infected adults (62–86%) had malformed wings, and their longevity was reduced compared with that of healthy adults. Infected S. exigua adults that seemed to be morphologically healthy were able to mate and produce viable offspring. The disease was detected in five of 12 groups of progeny produced by infected adults. However, the relative infection rate in the filial generation was low (2–5%). To our knowledge, this is the first evidence for a vertical transmission of helicosporidial infection.