Peroral infectivity of non-occluded viruses of Bombyx mori nucleopolyhedrovirus and polyhedrin-negative recombinant baculoviruses to silkworm larvae is drastically enhanced when administered with Anomala cuprea entomopoxvirus spindles.

Non-occluded viruses (NOVs) of Bombyx mori nucleopolyhedrovirus (BmNPV) are poorly infectious to silkworm larvae when administered by peroral inoculation, although they are highly infectious when injected into the insect haemocoel. In the present study, it is demonstrated that NOVs of BmNPV became highly infectious even through peroral inoculation when administered with spindles (proteinaceous structures) of Anomala cuprea entomopoxvirus (AcEPV). Marked enhancement of peroral infectivity of NOVs by AcEPV spindles (nearly 1000-fold higher in the strongest case) was observed in all growth stages of silkworm larvae tested (2nd to 5th instar). Similarly, peroral infectivity of polyhedrin-negative recombinants of BmNPV, which do not produce polyhedra, was also enhanced remarkably by AcEPV spindles. In contrast, spheroids (proteinaceous structures containing AcEPV virions) did not enhance the peroral infectivity of either NOVs or the recombinant BmNPV in silkworm larvae.