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50 word summary here before any deformed wings appear. This article explains how “invisible” DWV quietly drains nectar, shortens worker lives and undermines winter survival—and why breeding for viral resistance must join Varroa control in every beekeeper’s toolkit.

by the Scientific & Technical Working Group: Karl Colyer and Paul Verrier

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Why viral resistance needs to be part of the beekeeping conversation

Most beekeepers associate Deformed Wing Virus (DWV) with the obvious: crippled wings, crawling bees, and colonies that fail to make it through winter. But new research shows that even when no deformed wings are visible, DWV can quietly undermine a colony from within.

A recent study published in Scientific Reports (Ferreira et al., 2025) reveals how DWV affects the foraging behaviour of adult worker bees, with consequences that ripple through colony nutrition, resilience, and survival. The findings strengthen the argument that DWV resistance — not just Varroa control — must become a core part of sustainable beekeeping.

Not just a winter virus

DWV is now almost ubiquitous wherever Varroa destructor is present. While high virus levels cause the classic wing deformities, many infections are “covert”: bees look normal, fly normally, and continue working.

For years, these covert infections were assumed to be relatively harmless. This new study challenges that assumption.

The researchers experimentally infected newly emerged workers with DWV (without causing visible deformities) and compared them to protected control bees in full-sized colonies. They then followed these bees through their working lives, carefully recording when they started foraging, what they collected, how successful they were, and how long they lived.

What they found should concern every beekeeper.

DWV pushes bees to forage too early

Healthy worker bees normally spend the first part of their adult lives inside the hive, nursing brood and maintaining the colony, before transitioning to foraging later on. This balance is essential for colony stability.

DWV-infected bees, however, began foraging earlier than normal — a phenomenon known as precocious foraging. This is not a benefit to the colony. Early foragers are:

Less efficient
More likely to die
Replacing nurse bees before they should

The study showed that DWV-infected foragers also had shorter foraging lifespans, meaning they died sooner once they started flying. Over time, this drains the colony of both nurses and effective foragers.

In practical terms, DWV accelerates workforce burnout.

Nectar collection suffers — badly

Perhaps the most striking finding concerns nectar. Compared to healthy bees, DWV-infected nectar foragers:

Returned less often with nectar
Collected nectar with almost half the sugar concentration

On average, infected bees brought back nectar at around 13 % sugar, compared with 21 % for controls.

This matters enormously. Nectar sugar concentration determines:

Energy return per foraging trip
Honey yield
Ability to build winter stores

In late summer and autumn — exactly when colonies need to build reserves — low-sugar nectar means more flights, more energy spent, and less stored food.

Even if the colony looks busy, it may be quietly running a carbohydrate deficit.

A shift towards pollen — but not a solution

Interestingly, DWV-infected bees were more likely to collect pollen than nectar, and they collected normal-sized pollen loads.

At first glance, this might sound positive. But pollen cannot replace nectar:

Nectar (and honey) fuels flight, thermoregulation, wax production, and winter survival
Pollen supports brood rearing but cannot compensate for lost energy intake

The researchers suggest that DWV affects the bees’ nervous system, altering how they respond to sugar and possibly impairing memory and navigation. Infected bees appear more willing to accept poor nectar sources or abandon nectar for pollen altogether.

This creates a nutritional imbalance: protein without enough energy.

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Practical take‑aways for bee management by BIBBA Members

Control Varroa hard and early. Varroa is the main driver that turns low‑level DWV into serious infections; good Varroa control remains the single most effective DWV management tool.
Watch for subtle performance changes, not just deformed wings. Colonies that are light despite forage, need repeated feed, or show poor foraging activity compared with neighbours may be suffering from DWV‑related foraging impairment.
Support nutrition. Ensure access to good nectar and pollen sources, and don’t hesitate to feed when natural forage is poor, because DWV‑affected foragers will be less able to “make up the difference” for themselves.
Breed and select for resilience where possible. Lines that show better Varroa tolerance, stronger overwintering and good spring build‑up are probably coping better with DWV pressure and its hidden foraging costs.

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Looking forward

As pressure on forage increases and climate variability grows, colonies cannot afford to lose efficiency. Subtle losses add up. The message from this study is clear: DWV resistance matters, even when wings look perfect.

For beekeepers committed to sustainable, low-input systems, the future likely lies not in fighting symptoms, but in breeding bees that can live with the virus - and still do their job well.

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Notes from the Scientific & Technical Team….

The title seems to imply that the authors are studying Apis melifera ligustica (Italian honeybees and the most commonly kept species in the USA according to Wikipedia). But bees they term ‘Russian’ (but bred in the US) are unspecified in terms of their subspecies. Are they comparing like with like and could the differences identified actually just be a result of their genetic backgrounds?
It sounds as if the apiaries used were enormous. The methods section describes n=299 Russian colonies across just 2 apiaries. As such, with so many bees in one geographic area, maybe it’s not surprising that there is little forage to be had when ‘overwintered outside’ bees do fly - making each flight a ‘net cost’ to the colony. As such, when UK-based bees fly they might have a better chance of them finding enough forage to make it worth their while (both nectar but possibly more importantly pollen for early brood rearing). As such caution might be advised when applying these results to UK practice. Urban bees tend to have a greater variety of plants available to them locally.
The study seems to compare cold storage in North Dakota against shipping to and from an overwintering apiary in Mississippi. How much did transporting colonies contribute to the results? They consider the transport impact in terms of costs but not in terms of bee welfare.

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Why this matters for colony survival

The cumulative effect of these changes is profound:

Earlier foraging
Shorter worker lifespan
Reduced nectar intake
Lower honey production
Increased vulnerability during nectar dearths

A colony may survive the summer yet fail in autumn or winter, not because of starvation alone, but because DWV has quietly eroded its efficiency months earlier.

This helps explain why colonies with “manageable” Varroa levels can still collapse — especially under poor forage conditions or high colony density.

The case for viral resistance selection

Current management focuses heavily on mite control, and rightly so. But this study reinforces an uncomfortable truth:

Even low-level DWV infections cause real harm.

Chemical control can reduce mites, but it does not eliminate DWV. Resistant stocks, however, can reduce viral replication, limit behavioural disruption, and improve long-term resilience.

Traits already discussed within BIBBA circles, such as:

Varroa Sensitive Hygiene (VSH)
Suppressed mite reproduction
Survivorship without treatment

are also likely to reduce viral load and its behavioural impacts.

Selecting queens and colonies that cope better with DWV, not just mites, may be essential if we want bees that can forage efficiently in real-world conditions.