Understanding Varroa and its Biology
Varroa destructor is the parasitic mite that threatens honey bees worldwide. It weakens bees by feeding on their fat bodies and spreads viruses that can collapse colonies. To manage Varroa effectively, we first need to understand how it lives, spreads, and affects our bees and then use biology-aware strategies to control it.
(Doubleduff, 2023)
Introduction What is varroa ?
Varroa destructor is a reddish-brown, oval mite that parasitises European honey bees (Apis mellifera). It feeds on fat body tissue, weakening immunity and shortening the bee's lifespan. The real damage often comes from virus transmission (especially DWV), which leads to deformed wings, patchy brood, dwindling populations, and eventual colony collapse.
(Doubleduff, 2023)
Orgin and Spread of Varroa
Varroa co-evolved with Asian honey bees (Apis cerana), where strong hygienic behaviours (rapid uncapping and removal) kept mite reproduction in check. After the host jump to European honey bees (A. mellifera), the parasite met a host that lacked those precise reflexes, turning a contained parasite into a global driver of colony decline.How it moved: Varroa spreads along the same lines humans do: cargo routes, pollination movements, and hive trade. Swarms can shelter in containers; drifting and robbing move mites locally; interstate pollination and equipment sharing move them regionally. This is why port awareness, roadside checks, and beekeeper monitoring matter more than borders.Regional timeline & implications (for SA):NZ (2000s): Shift from theory to day-to-day management; practical routines (monitor by method and threshold; rotate treatment families) became normal.Australia (2022): Detection in NSW ended eradication hopes and reset policy toward long-term management.South Australia (now): The Riverland is a risk corridor due to freight + pollination traffic. Early adoption of standard monitoring and shared thresholds among hobbyists and commercial beekeepers limits regional flare-ups.
Varroa Mite's Life Cycle
Varroa is basically a parasite that times its life around the brood. A fertilised female mite sneaks into a brood cell just before it gets capped, usually a drone cell, because drones stay sealed longer. Once sealed in, she lays a male egg first, then a few female eggs. The young mites grow alongside the developing bee, changing from egg → protonymph → deutonymph → adult. When the bee hatches, the mother and her adult daughters crawl out with it to find new bees to ride on, while the male dies inside the cell.Why drone brood makes the problem worse: Drone cells are capped for around 24 days (workers only 21). That extra 3 days means the mite family has time to raise more daughters, so drone-heavy colonies can quietly turn into “mite factories.” In commercial yards overseas, some keepers use this to their advantage by deliberately giving the mites drone brood to lay in, then cutting those frames out before emergence. What this means for management: When most mites are under cappings, chemical treatments can only touch a small part of the population. If you create or catch a broodless period (like by isolating the queen), nearly all mites are riding adult bees, making it the best time to use oxalic acid or other phoretic treatments. Using drone frames as “bait” can pull the mites into one place and make it easier to remove them.
(Doubleduff, 2023)
How Varroa Affects Bees
(Doubleduff, 2023)
Varroa doesn’t just suck the bees’ blood like people used to think. It actually feeds on the bees’ fat bodies, which are organs that store energy and help detox chemicals. This weakens the bees from the inside out their immune systems crash, they burn out faster, and the queen’s laying rate can drop.But the real killer is viruses, especially Deformed Wing Virus (DWV). Varroa mites carry and spread these viruses directly into the bee’s blood when they feed. Even a small number of mites can blow up into huge problems if DWV gets out of control. You’ll start seeing: Bees with crumpled or missing wings, Patchy brood patterns, Foragers not returning, and Colonies that dwindle away over winter.This is why just counting mites on bees doesn’t tell the full story what really matters is the virus load behind those numbers. Beekeepers overseas said that once you can see DWV, it’s already too late.
Varroa in the Hive: How it Spreads
No matter how careful you are, mites move. There’s no such thing as a perfect barrier. Within a yard, bees drift into the wrong hives, rob weak colonies, or swarm and take mites with them. Once a few colonies are infested, the mites spread like smoke. Between yards: shared tools, borrowed frames, and even pollination transport move mites further. One commercial beekeeper said he’s seen bees from one yard visiting another more than a kilometre away it happens without us noticing. What actually works is slowing it down: Sterilise hive tools between each site (a quick dip in methylated spirits or flame works). Quarantine new or returning colonies for two brood cycles before merging. Keep a basic record of date, yard, number of mites, what test you used, and what treatment you did.
Why Understanding Biology Matters for Control
(Doubleduff, 2023)
You can’t manage varroa by the calendar anymore; it has to be based on what’s happening inside the brood. Broodless windows (natural or made): When there’s no capped brood, every mite is exposed on adult bees. That’s the perfect moment to treat them with oxalic acid because it hits them all at once. A frame isolator makes this easier: lock the queen on one frame, wait 24 days, remove that frame before the drones hatch, then treat. Drone-trap & cut: This uses the mite’s weakness. They love drone brood, so if you give them a special drone frame, they’ll lay there first. Once capped, you take that frame out and destroy it. That can drop mite levels by 30–40% without chemicals. Temperature-sensitive treatments: Organic acids like formic and thymol work really well overseas, but only inside a safe temperature range. If it’s too hot, queens can stop laying or die. That’s why planning treatment windows around the Riverland climate is so important. Rotate and go easy: Keep changing what treatment group you use each season to stop mites building resistance. And don’t use weak or continuous doses that just teaches mites to survive and messes with the bees’ pheromone communication (which affects their hygiene behaviour).
References:
Doubleduff, J. (2023, December 12). Varroa presentation [PowerPoint slides]. Personal communication forwarded by K. — received January 3, 2024.
Information on Varroa biology and management was compiled through multiple interviews with experienced Australian and New Zealand beekeepers, queen breeders, and researchers conducted between july and september 2025.