A grounded synthesis of representative open-access papers on the non-virus pests and pathogens of honey bees. Every claim is traceable to a cited study; curated overview, not exhaustive.
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Beyond Varroa and the viruses it spreads, honey bees face a diverse roster of pathogens and pests spanning four kingdoms: bacteria, fungi, microsporidian parasites, and arthropod pests. These rarely act in isolation — they interact with each other and with Varroa — and several are notifiable diseases or invasive biosecurity threats (Holt 2016; Bahreini 2015).
Nosema (now reclassified into Vairimorpha) are obligate intracellular microsporidia that infect the honey bee midgut, with N. ceranae having largely displaced N. apis in A. mellifera worldwide. Their virulence is debated and their management remains challenging (Holt 2016). They also interact with other stressors, co-parasitising bees alongside Varroa (Bahreini 2015). See Nosema / Vairimorpha.
Two bacteria cause the classic foulbroods: Paenibacillus larvae (American foulbrood), a spore-forming, highly contagious and often notifiable killer of brood, and Melissococcus plutonius (European foulbrood). Both kill larvae and, in severe cases, whole colonies.
The fungus Ascosphaera apis causes chalkbrood, mummifying larvae; its spores are remarkably persistent and can even be carried in wax foundation (Cheng 2022).
Several arthropods parasitise or scavenge colonies: the invasive small hive beetle (Aethina tumida), the internal tracheal mite (Acarapis woodi) — historically significant but overshadowed by Varroa (Underwood 2009) — and Tropilaelaps, a brood mite that is a major biosecurity threat if it spreads beyond Asia.
This roster matters because these pathogens interact with the Varroa–virus complex and with each other, and because some (Tropilaelaps, small hive beetle) are expanding their range. Each is treated in its own grounded page; together they round out the threat landscape beyond the viruses catalogued in the virus section.
Holt et al., Journal of Economic Entomology 2016 · 29 citations — Reviews the mixed virulence reports and management difficulty of Nosema.
Bahreini & Currie, Journal of Invertebrate Pathology 2015 · 9 citations — Quantifies Nosema–Varroa co-parasitism costs.
Cheng et al., Frontiers in Microbiology 2022 · 12 citations — Ascosphaera apis and associated pathogens.
Underwood & Currie, Journal of Economic Entomology 2009 · 12 citations — Tracheal-mite control alongside Varroa treatment.
Curated synthesis of representative and most-cited studies — not exhaustive. Explore via search. Subtopics: Nosema · American foulbrood · European foulbrood · Chalkbrood · Small hive beetle · Tracheal mites · Tropilaelaps.