Table 2.

Symptoms of viral infections in A. mellifera. Tissue tropism refers to the organs in which the virus was found. Symptoms report the physical and physiological effect of viruses as observed in honey bees. Only viruses with known symptoms are reported here.

Virus	Tropism	Symptoms	Refs
Acute bee paralysis virus complex	Nervous system, cytoplasm of fat body cells, brain and hypopharyngeal glands	Trembling, inability to fly, gradual darkening and loss of hair from the thorax and abdomen, crawling on the ground and upward on grass, rapid death for highly infected bees	[84,85,86]
Apis iridovirus	NA	Iridescence of most internal organs	[87]
Apis mellifera filamentous virus	NA	Milky-white hemolymph	[88]
Bee virus X	NA	Shortened lifespan of adult bees	[89]
Bee virus Y	NA	Shortened lifespan of adult bees	[37]
Black queen cell virus	Gut tissue	Yellowish queen larvae with sac-appearance that resembles SBV and with time evolves to dark brown, infected pupae turn brown and die, dark brown to black colored walls in queen cells, significantly shortened life span in adult bees	[36,84,90]
Chronic bee paralysis virus	Nervous system, alimentary tract, mandibular and hypopharyngeal glands	Syndrome 1: trembling of the wings and bodies, bloated abdomen, inability to fly, crawling on the ground and upward on grass, gather in groups in the warmest areas of the nest, death within few days	[84,91]
		Syndrome 2 (’black robbers’): hairless (thus appearing smaller), darker, greasy in appearance, shiny, suffer nibbling attacks by the healthy bees, death within few days
Cloudy wing virus	Tracheal tissue and thoracic muscles	Opaque wings, shortened lifespan of adult bees	[92,93]
Deformed wing virus	Whole body, including the queen ovaries, queen fat body, spermatheca, and drone seminal vesicles, tissues of wings, head, thorax, legs, hemolymph and gut	Crumpled or aborted wings, shortened abdomens, paralysis, severely shortened adult life span for emerging worker and drone bees, modified responsiveness to sucrose, impaired learning, impaired foraging behavior	[59,64,94,95,96]
Invertebrate iridescent virus Type 6	NA	Flightless clustering bees	[87]
Sacbrood virus	Hypopharyngeal glands of worker bees, cytoplasm of fat, muscle and tracheal-end cells of larvae	Pupation failure, ’sac’ phenotype: swollen larvae filled with ecdysial fluid full of viral particles, precocious foraging, reduction of adult life span and metabolic activities, impaired foraging activity	[97,98,99]
Slow bee paralysis virus	Nervous system	Paralysis of the two anterior legs a day or two before death	[89]