The Varroa Crisis & Colony Losses

The Scope

The Bee Informed Partnership's annual colony loss survey - the most comprehensive longitudinal dataset on US colony health - has documented total annual colony losses (April to April) averaging 30 to 45 percent nationwide since the survey began in 2006. Winter losses alone average 25 to 35 percent. Summer losses, historically minimal, now average 20 to 25 percent.

Before Varroa, annual colony losses averaged roughly 10 to 15 percent - primarily from queenlessness, starvation, and environmental events. The current loss rate represents a roughly threefold increase over historical baselines. The US managed colony count has remained relatively stable (around 2.5 to 2.7 million colonies) only because beekeepers replace lost colonies through splitting survivors, purchasing packages and nucleus colonies, and importing queens. This replacement rate masks the underlying mortality: the beekeeping industry is running on a treadmill, replacing a third to nearly half of its colonies every year just to maintain standing numbers.

The economic cost of colony replacement is substantial. A package of bees costs $150 to $200. A nucleus colony costs $200 to $300. The labor, equipment, and management time for colony replacement adds further cost. The Bee Informed Partnership estimates annual replacement costs to the US beekeeping industry at approximately $2 billion. This cost is ultimately passed to agriculture through pollination service fees, which have risen from roughly $30 per colony in the 1990s to $200 or more for almond pollination in California.

The Mite

Varroa destructor is an external parasitic mite that feeds on the fat body of honey bees - both adult bees and developing pupae. The mite's life cycle is intimately synchronized with the bee's reproductive cycle: female mites enter brood cells just before capping, reproduce on the developing pupa, and emerge with the adult bee. A mite feeding on a pupa reduces the bee's emergence weight, shortens her lifespan, compromises her immune function, and - most critically - vectors at least five viral pathogens, including deformed wing virus (DWV), which causes wing deformity, reduced lifespan, and colony collapse at high infestation levels.

The mite reproduces exponentially within a colony. A colony that starts spring with 50 mites can have 5,000 or more by late summer if untreated. At that point, the viruses vectored by the mites overwhelm the colony's immune capacity. The bees emerging in late summer and fall - the generation that must survive through winter - emerge with shortened lifespans, compromised fat bodies, and viral loads that make winter survival impossible. The colony dies between October and February. The pattern is predictable, well-documented, and repeats across millions of colonies annually.

The Treatment Landscape

Six compounds are currently registered for Varroa treatment in the US:

• Amitraz (Apivar strips) - The most widely used treatment. A formamidine acaricide. Effective but resistance has been documented in some US populations.
• Oxalic acid (Api-Bioxal, vaporization) - An organic acid that kills mites on adult bees. Does not penetrate cappings. Requires broodless or near-broodless conditions for maximum efficacy.
• Formic acid (Formic Pro, MAQS) - An organic acid that penetrates cappings, killing mites in brood cells. Temperature-sensitive. Can damage queens at high ambient temperatures.
• Thymol (Apiguard, ApiLife Var) - A plant-derived compound. Moderate efficacy. Temperature-dependent.
• Tau-fluvalinate (Apistan) - A pyrethroid. Historically the first widely used Varroa treatment. Resistance is now widespread. Largely ineffective in many US populations.
• Coumaphos (CheckMite+) - An organophosphate. Resistance documented. Residues accumulate in beeswax. Limited use.

The treatment toolkit is narrow and narrowing. Tau-fluvalinate and coumaphos are functionally obsolete due to resistance. Amitraz resistance is emerging. This leaves organic acids (oxalic, formic) and thymol as the reliable treatments - compounds that are effective but operationally demanding (temperature sensitivity, timing requirements, labor intensity).

No new synthetic acaricide has been registered for Varroa in the US in over a decade. The market is too small to attract pharmaceutical investment: the US beekeeping industry's total treatment expenditure is roughly $50 to $80 million per year - a rounding error in pharmaceutical economics. Novel compounds in development (lithium chloride, RNAi-based treatments) show promise but face lengthy regulatory approval timelines.

The Breeding Hope

The long-term solution to Varroa is widely believed to be genetic: breeding honey bees with heritable resistance traits that reduce mite reproduction. Several resistance mechanisms have been identified:

• Varroa Sensitive Hygiene (VSH). Bees detect and remove mite-infested pupae from capped cells, interrupting the mite's reproductive cycle. Selected for by the USDA Baton Rouge Bee Lab since the 1990s.
• Grooming behavior. Adult bees physically remove mites from their own bodies or nestmates' bodies, damaging or killing the mites. More prevalent in some genetic lines.
• Reduced mite reproduction. Some bee genotypes support lower mite reproductive success - mites enter brood cells but produce fewer viable offspring. The mechanism is not fully understood.

The USDA's breeding programs (Baton Rouge Lab, Purdue University's Indiana program) have produced genetic lines with meaningful mite resistance. The challenge is scaling: breeding program queens must be propagated through multiple generations to supply commercial beekeeping, and the resistance traits can dilute through open mating with non-resistant drones. Instrumental insemination preserves genetics precisely but doesn't scale to industry needs.

Feral bee populations that survive without treatment - documented by Thomas Seeley in the Arnot Forest and in several other long-term studies - demonstrate that Varroa-resistant honey bee populations can evolve naturally. The selection pressure is extreme (untreated colonies have roughly 10-20% annual survival rates initially), but the survivors carry genetic combinations that confer resistance. Whether these traits can be captured and bred into managed populations at commercial scale remains an open research question.

Where The Apiary Project Stands

The Apiary Project's position on the Varroa crisis centers on three priorities:

1. Increased federal research funding. Current USDA funding for all pollinator research is approximately $20 million per year. This funds research on Varroa, pesticides, nutrition, disease, native pollinators, and basic biology - across all institutions. For context, the pollination services at risk are valued at $20-30 billion annually. The research investment represents roughly 0.1% of the value at stake. Breeding programs, novel treatment development, and basic mite biology research all need substantially more funding than they currently receive.
2. Accelerated treatment approval. The regulatory pathway for new Varroa treatments should be streamlined to reflect the urgency of treatment resistance. Novel compounds that demonstrate safety and efficacy in field trials should have expedited EPA registration. The current timeline - often 5 to 10 years from development to registration - means that by the time a new treatment reaches beekeepers, the resistance landscape may have already shifted.
3. Monitoring infrastructure. Mandatory mite monitoring as a condition of interstate colony movement (particularly for migratory beekeeping operations that move colonies for pollination) would establish baseline surveillance data and incentivize proactive management. The Bee Informed Partnership's Tech Transfer Teams provide monitoring services in some states; this model should be expanded nationally with federal support.

Varroa is not going away. The mite is a permanent member of the North American apicultural ecosystem. The question is not whether beekeepers will have to manage it, but whether the tools and genetic resources they need to manage it will be available, affordable, and effective. That outcome depends on research investment decisions being made now.