Growth Characteristics and Competitive Abilities of a Nucleopolyhedrovirus and an Entomopoxvirus in Larvae of the Smaller Tea Tortrix, Adoxophyes honmai (Lepidoptera: Tortricidae)

We examined the effect of a mixed infection by Adoxophyes honmai nucleopolyhedrovirus (AdhoNPV) and A. honmai entomopoxvirus (AdhoEPV) on time to death of hosts and virus multiplication rate. Neonates and fourth-instar larvae of A. honmai were simultaneously or sequentially exposed to lethal concentrations of AdhoNPV and AdhoEPV. The number of viral occlusion bodies (OBs) that each virus produced was quantified and compared between mixed-infected and single-infected hosts. When each was separately introduced into fourth-instar larvae, AdhoNPV and AdhoEPV killed the host by 9 to 11 and 18 to 24 days postinfection (p.i.), respectively. The average number of OBs at time of host death was about 1010 polyhedra/insect for AdhoNPV and 108.5 spheroids/insect for AdhoEPV. Fourth-instar larvae simultaneously inoculated with AdhoNPV and AdhoEPV died 9 to 11 days p.i. In this simultaneous mixed-infection treatment, AdhoEPV OB yield was significantly reduced, whereas AdhoNPV OB production was unaffected. However, when neonate larvae were exposed first to AdhoEPV and then to AdhoNPV only after molting to the fourth instar, AdhoNPV OB production was reduced and its final yield decreased to a few percent of the yield obtained in single-infected hosts, whereas AdhoEPV OB production was unaffected. These results suggest that the sequence or timing of infection significantly affects the OB production of both viruses. In larvae infected with each virus in sequence, the numbers of hemocytes containing both OB types were significantly fewer than that expected by random infection. These results suggest that AdhoNPV and AdhoEPV could reduce their fitness due to interference between them.