VIRUSES OF INSECTS

The global decline of insects has made headline news in recent years, and it is estimated that a 9% decline in total terrestrial insect abundance has occurred each decade since the early 1990s. The first documented disease of insects was a jaundice disease virus of the silkworm. Notably, in the 1940s, only two groups/or genera of viruses were known to infect insects: those that infect Lepidoptera (we know those today as baculoviruses) and those that cause sacbrood disease in honeybees (belonging to the positive sense, single-stranded RNA picorna-like viruses). Recent studies using large transcriptomic sequence collections of invertebrates have yielded an unprecedented diversity of novel RNA viruses. Sequence probing for RNA viruses in all 34 extant orders of Hexapoda, altogether discovered nearly 500 viral RNA-directed RNA polymerase sequences with similarity to negative single-stranded RNA viruses. These were identified in members of 324 arthropod species. Here, we provide an overview of the diversity of viruses found to infect insects. However, we do go on to focus on a key insect species, the European honeybee Apis mellifera, which is facing unprecedented threat by numerous ssRNA virus infections. Due to the importance of the European honeybee to global pollination services, we specifically discuss within this chapter the role of Deformed wing virus in the demise of the honeybee worldwide.