Segregated transmission of co-occluded baculoviruses limits cellular coinfection and virus-virus interactions

Baculovirus occlusion bodies (OBs) are polyhedrin-rich structures that mediate the collective transmission of tens of viral particles to the same insect host. In addition, in multiple nucleopolyhedroviruses, occlusion-derived viruses (ODVs) form nucleocapsid aggregates that are delivered to the same host cell. It has been suggested that, by favoring coinfection, this transmission mode promotes evolutionarily stable interactions between different baculovirus variants. To investigate this, we obtained OBs from cells coinfected with two viral constructs, each encoding a different fluorescent reporter, and used them for inoculating Spodoptera exigua larvae. Microscopy analysis of midguts revealed that the two reporter genes were typically segregated into different infection foci, suggesting that ODVs do not promote the coinfection of cells with different baculovirus genetic variants. However, a polyhedrin-deficient mutant underwent inter-host transmission by exploiting the OBs of a fully-functional virus and re-acquired the lost gene through recombination, demonstrating cellular coinfection. Our results suggest that viral spatial segregation during transmission and primary infection limits interactions between different baculovirus variants, but that these interactions still occur episodically.