Vertical transmission of nucleopolyhedrovirus in the silkworm, Bombyx mori L

Abstract

Nucleopolyhedrovirus (NPV) was tested for vertical transmission in the silkworm, Bombyx mori. Fifth instar larvae were exposed to four different dosages of BmNPV (830, 1300, 1800, and 2000 OBs/larva) and a dosage of about 2000 OBs/larva was found suitable for obtaining infected adults. Histopathological studies revealed the infection in susceptible tissues and organs initially, and at later stages of infection cycles the spermatocytes and nurse cells in the young oocytes were infected in the larval rudiments of testis and ovary, respectively. The mating of infected females with uninfected males resulted in significant reduction in fecundity (P<0.01) and hatching of eggs (P<0.001) due to transovarial transmission of BmNPV. Mating tests of uninfected females and infected males also confirmed venereal transmission as there was a significant reduction in hatching of eggs (P<0.01). Further, among the F₁ hybrid offspring (infected female × uninfected male) that were infected transovarially, larval progeny died at first and second instar stages, whereas those infected venereally developed acute lethal infection late and died by the end of third and fourth instar stage. PCR amplification and sequencing of 473 bp of immediate early-1 (ie-1) gene of BmNPV isolated from the viral-infected parent and the F₁ offspring confirmed that the viral infection is vertically transmitted to the progeny.