Mixtures of Insect-Pathogenic Viruses in a Single Virion: towards the Development of Custom-Designed Insecticides

ABSTRACT

Alphabaculoviruses (Baculoviridae) are pathogenic DNA viruses of Lepidoptera that have applications as the basis for biological insecticides and expression vectors in biotechnological processes. These viruses have a characteristic physical structure that facilitates the transmission of groups of genomes. We demonstrate that coinfection of a susceptible insect by two different alphabaculovirus species results in the production of mixed-virus occlusion bodies containing the parental viruses. This occurred between closely related and phylogenetically more distant alphabaculoviruses. Approximately half the virions present in proteinaceous viral occlusion bodies produced following coinfection of insects with a mixture of two alphabaculoviruses contained both viruses, indicating that the viruses coinfected and replicated in a single cell and were coenveloped within the same virion. This observation was confirmed by endpoint dilution assay. Moreover, both viruses persisted in the mixed-virus population by coinfection of insects during several rounds of insect-to-insect transmission. Coinfection by viruses that differed in genome size had unexpected results on the length of viral nucleocapsids, which differed from those of both parental viruses. These results have unique implications for the development of alphabaculoviruses as biological control agents of insect pests.

IMPORTANCE Alphabaculoviruses are used as biological insecticides and expression vectors in biotechnology and medical applications. We demonstrate that in caterpillars infected with particular mixtures of viruses, the genomes of different baculovirus species can be enveloped together within individual virions and occluded within proteinaceous occlusion bodies. This results in the transmission of mixed-virus populations to the caterpillar stages of moth species. Once established, mixed-virus populations persist by coinfection of insect cells during several rounds of insect-to-insect transmission. Mixed-virus production technology opens the way to the development of custom-designed insecticides for control of different combinations of caterpillar pest species.