The hidden players: exogenous (nonendogenous) viruses in parasitoid ecology and biological control

Parasitoids are essential components of terrestrial ecosystems and key agents in biological pest control. Some species rely on endogenous viruses integrated into their genomes to enhance parasitism success. However, most parasitoids lack these mutualistic viruses and instead carry diverse nonendogenized DNA and RNA viruses, referred to as exogenous, whose roles remain far less understood. Here, we synthesize current knowledge on exogenous viruses associated with parasitoids, including their diversity, transmission, replication strategies, and infection outcomes. Despite the extensive diversity of parasitoids, our review shows that viruses have been characterized in only 34 species, with 62 RNA and 11 double-stranded DNA viruses identified. We also examine the implications of virus-parasitoid-host interactions for ecological dynamics and biological control, emphasizing how viruses may shape host-parasitoid relationships, competition, and pest suppression. Advancing our understanding of these exogenous viruses will provide new insight into virus-host evolution, ecosystem processes, and pest management.