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New Zealand has experienced an unusual winter, and as the first signs of spring begin appearing, beekeepers may want to pay particularly close attention to what is happening inside their hives.

June 2026 was officially New Zealand's warmest June on record, according to Earth Sciences New Zealand (formerly NIWA). The nationwide average temperature reached 10.6°C – 1.9°C above the 1991–2020 June average. In Christchurch, temperatures even reached 26°C on 20 June, setting a new national June temperature record.

July remained relatively mild overall, ranking as New Zealand's 12th-warmest July since the national seven-station temperature series began in 1909.

So, what could an unusually warm start to winter mean for our bees – and, importantly, for Varroa?

The Link Between Brood and Varroa

To understand why weather matters, we first need to look at the relationship between Varroa destructor and honey bee brood.

Varroa mites reproduce inside capped brood cells. A female mite enters a cell before it is capped and reproduces while the developing bee is inside. When the new adult bee emerges, mature female offspring can emerge with it and continue the infestation cycle.

This means brood availability is an important factor in determining how quickly a Varroa population can grow.

During periods when a colony has little or no brood, Varroa reproduction is interrupted. In fact, Biosecurity New Zealand specifically notes that broodless periods can reduce mite loads within colonies.

The opposite is also important to consider: if conditions encourage colonies to maintain brood for longer through winter, or begin increasing brood production earlier in spring, mites may have additional opportunities to reproduce.

Could a Warm Winter Give Varroa a Head Start?

Potentially – but it's not quite that simple.

International research has found a relationship between seasonal temperatures, brood availability and Varroa populations.

One study published in Scientific Reports found that higher seasonal temperatures can influence Varroa infestation through their effects on honey bee populations and brood availability. The researchers noted that rising temperatures in late winter can trigger brood production, and because Varroa reproduction depends on the presence of brood, extended colony activity can favour mite population growth.

Other research has similarly found that warmer winters can increase the duration of brood rearing, potentially allowing Varroa populations to begin increasing earlier.

That doesn't mean a warm June guarantees high Varroa levels in New Zealand this spring.

Colony strength, location, forage availability, queen behaviour, previous treatments, reinvasion from neighbouring colonies and weather over the coming months will all play a part.

What it does mean is that this may not be the year to assume your Varroa population is behaving according to the calendar.

Spring Can Change Things Quickly

As spring progresses, colonies naturally begin expanding.

Queens increase their laying, brood nests grow and bee populations start building towards the productive season ahead.

Unfortunately, that growing brood nest also provides Varroa with increasing reproductive opportunities.

A colony that appears strong can therefore still have a developing mite population hidden largely within its capped brood.

This is one reason why simply looking for mites on adult bees isn't a reliable way of determining the level of infestation.

Biosecurity New Zealand advises beekeepers to actively monitor Varroa levels rather than relying on visual observation alone. Recommended monitoring techniques include alcohol washes, sugar shakes and sticky boards.

Don't Treat Varroa by the Calendar Alone

For many beekeepers, Varroa management naturally falls into a familiar annual routine.

But bees don't read calendars – and neither does Varroa.

When seasonal conditions vary significantly from one year to another, colony development can vary too. A treatment date that worked well last season doesn't necessarily tell you what the mite population is doing inside your colonies today.

New Zealand Varroa guidance specifically warns against relying solely on calendar-based treatment. Monitoring allows beekeepers to make decisions based on what is actually happening in their colonies.

Ideally, monitoring shouldn't stop once a treatment has been applied either.

Monitoring before, during and after treatment can help establish the level of infestation, assess whether control has been successful and identify mite populations that rebound or enter the colony through reinvasion.

Reinvasion Is Another Piece of the Puzzle

Even a colony that has been successfully treated isn't necessarily protected for the rest of the season.

Varroa can be introduced again through drifting and robbing bees, particularly where neighbouring colonies have high mite loads.

Biosecurity New Zealand highlights reinvasion as an important consideration in Varroa management and encourages communication between neighbouring beekeepers where possible.

Research has also demonstrated that brood availability can play a role in Varroa reinvasion during autumn and winter.

For commercial operators with multiple apiaries – and hobbyists living in areas with plenty of backyard hives – this makes ongoing monitoring particularly valuable.

What Should Beekeepers Be Doing Now?

As we move from winter into spring, it's a good opportunity to establish a baseline for your colonies rather than waiting until Varroa becomes an obvious problem.

Consider:

• Checking Varroa levels now using an appropriate monitoring method.

• Recording your results so you can see how mite levels change as spring progresses.

• Looking at the amount of brood present, rather than assuming colony development is the same as it was at this time last year.

• Monitoring before and after treatment to determine whether the treatment has achieved the expected result.

• Remaining alert for reinvasion, particularly where other apiaries are located nearby.

• Following the label directions and New Zealand regulatory requirements for any registered Varroa treatment you use.

• Considering your overall Varroa programme for the season rather than relying repeatedly on a single treatment approach.

The Take-Home Message

New Zealand's record-breaking June doesn't necessarily mean we're heading for a record-breaking Varroa season.

But it does provide a timely reminder that Varroa management should respond to what is happening in the hive – not simply what date appears on the calendar.

Weather influences colony behaviour. Colony behaviour influences brood production. And brood availability is closely connected to Varroa reproduction.

As spring brood production begins to accelerate, now is a good time to find out exactly where your colonies stand.

Monitor early. Know your mite levels. Treat appropriately. And check again afterwards.

A little extra vigilance now could make a considerable difference later in the season.

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Sources & Further Reading

Earth Sciences New Zealand (formerly NIWA) – Climate Summary for June 2026: New Zealand's warmest June on record
https://niwa.co.nz/climate-and-weather/monthly/climate-summary-june-2026

Earth Sciences New Zealand – Climate Summary for July 2026
https://niwa.co.nz/climate-and-weather/monthly/climate-summary-july-2026

Biosecurity New Zealand / MPI – Guidance for Beekeepers: How do I tackle Varroa?
https://www.mpi.govt.nz/dmsdocument/56599/direct/

Biosecurity New Zealand / MPI – Re-imagining Varroa Monitoring: A Practical Approach
https://www.mpi.govt.nz/dmsdocument/59209/direct

Smoliński et al. – Raised seasonal temperatures reinforce autumn Varroa destructor infestation in honey bee colonies, Scientific Reports.
https://pmc.ncbi.nlm.nih.gov/articles/PMC8593171/

Calovi et al. – Warmer autumns and winters could reduce honey bee overwintering survival with potential risks for pollination services, Scientific Reports.
https://www.nature.com/articles/s41598-024-55327-8

Giacobino et al. – Varroa destructor re-invasion dynamics during autumn and winter in Apis mellifera colonies from a temperate climate, Journal of Invertebrate Pathology.
https://pubmed.ncbi.nlm.nih.gov/36708917/