Transovarial Transmission of Nosema Pyrausta in Three Generations of Ostrinia Nubilalis in Laboratory Tests

The microsporidium Nosema pyrausta (Paillot) (Nosematidae) is a widespread and persistent entomopathogen with integrated pest management implications. Nosema pyrausta is capable of horizontal and vertical transmissions in Ostrinia nubilalis (Hübner) (Lepidoptera: Crambidae) populations. After experimental per os infection, N. pyrausta virulence decreased with the instar of the host larvae used. At a dosage of 100,000 spores per fourth instar, 47% pupae and 36% adults survived and gave rise to transovarially infected offspring. The infection persisted through three laboratory generations of the host with prevalence levels ranging between 29 and 92%. Mature microsporidian spores were not found in smears prepared from the eggs laid by infected females, but cryosections demonstrated parasite cells within the host egg’s cytoplasm. A short region of N. pyrausta hexokinase was amplified using cDNA samples from infected females’ eggs, confirming the expression of the parasite’s DNA. Thus, vertical transmission of N. pyrausta is achieved through infection of insect eggs with prespore stages of the parasite.