Pest Management

Part of Beekeeping

Bee colonies face a range of parasites, predators, and pests that can devastate populations within a single season. In a post-industrial context where synthetic miticides may be unavailable, knowing how to manage varroa mites, wax moths, small hive beetles, and other pests using physical methods, natural acids, and essential oils is an essential skill. Early detection and systematic treatment cycles make the difference between a thriving apiary and repeated colony losses.

Varroa Destructor

Varroa is a parasitic mite that arrived from Asian honey bees (Apis cerana) in the mid-20th century and now affects Apis mellifera worldwide. A single female mite enters a brood cell just before capping, lays eggs on the developing pupa, and daughters mate with their brothers before emerging with the new bee. The mites weaken adult bees, deform wings, and transmit viruses — particularly Deformed Wing Virus (DWV), which renders newly emerged bees unable to fly.

Identifying Varroa Infestation

• Adult mites are visible to the naked eye: 1–1.5 mm, oval, reddish-brown, flat, with 8 legs. Look on adult bees between abdominal segments, especially on white newly-emerged bees (darker mites are easier to see on pale bees).
• Deformed Wing Virus symptoms: Newly emerged bees with crumpled, shriveled wings unable to fly, stumbling at the hive entrance. This symptom appears when varroa infestation is already severe.
• Alcohol wash test (most accurate quantification method):
  1. Collect approximately 300 bees (about 100 mL) from a brood frame into a jar of 70% alcohol.
  2. Shake vigorously for 60 seconds.
  3. Pour through a white mesh strainer. Count mites on the strainer and in the alcohol.
  4. Mite load = (mites counted / 300) × 100 = mites per 100 bees.

Mite Load (per 100 bees)	Risk Level	Action Required
0–1%	Low	Monitor monthly
1–3%	Moderate	Treat within 4–6 weeks
3–5%	High	Treat immediately
> 5%	Critical	Treat immediately; colony may be beyond saving

Varroa Treatment Without Synthetic Miticides

Oxalic acid (OA) is the most effective organic treatment and is used worldwide including in certified organic apiaries.

Vaporization (sublimation) — most effective method:

• Heat 1 g of oxalic acid crystals in a vaporizer inside the closed hive for 2.5 minutes.
• Treat 3 times at 5-day intervals during a broodless period (winter, after a split, or after removing all capped brood).
• During broodless periods, mites are all on adult bees (phoretic phase) and fully exposed to vapor.
• Efficacy: 95–99% in broodless colonies; 60–80% when brood is present (mites in sealed cells are protected).

Wear a respirator and goggles when handling oxalic acid crystals or working near a vaporizer. Oxalic acid vapor damages lungs and eyes.

Dribble method (no vaporizer needed):

• Mix 35 g oxalic acid in 1 liter of 1:1 sugar syrup.
• Dribble approximately 5 mL per seam of bees (between frames) — total 30–50 mL per hive.
• Use only once per year (high dose to bees) and only in broodless conditions.
• Efficacy: lower than vaporization, especially in spring; reserve for situations where no vaporizer is available.

Thymol (from thyme essential oil):

• Available as commercial preparations (ApiGuard, Thymovar) or can be prepared from food-grade thymol crystals.
• Place 25 g of thymol in a gel or crystal form on the frame tops. Replace after 2–3 weeks; apply two treatments.
• Effective in temperatures of 15–30°C; ineffective below 15°C (thymol does not vaporize adequately in cold).
• Efficacy: 80–95% when temperatures are suitable.

Drone brood removal:

• Varroa reproduces preferentially in drone brood (higher reproduction success). Frames fitted with larger drone-sized foundation attract disproportionate mite reproduction.
• Allow bees to fill a drone-size frame, then remove and freeze the frame before drones emerge. This removes a large proportion of the mite population without chemicals.
• Labor-intensive but valuable as part of an integrated strategy.

Wax Moths

Two species — Greater Wax Moth (Galleria mellonella) and Lesser Wax Moth (Achroia grisella) — lay eggs in stored comb and in weak hives. Larvae tunnel through wax, consume pollen, cocoons, and beeswax, and can destroy a full box of comb in 2–3 weeks.

Prevention in Active Hives

A strong colony protects itself: guard bees kill adult wax moths at the entrance. Wax moth damage in active hives is almost always a symptom of colony weakness, not a cause. If wax moths are damaging comb inside an active hive, the colony is too small for the space provided.

• Match hive space to colony size: A colony covering only 4–5 frames should be in a 5-frame nucleus box, not a 10-frame box. Bees cannot patrol unused space.
• Keep the entrance small: Reduce the entrance in autumn and winter to a gap bees can defend (10–15 cm wide, 7–8 mm tall for temperate climates; 5–7 cm for small colonies).

Protecting Stored Comb

Empty supers and brood comb stored over winter are highly vulnerable.

Physical methods:

• Freezing: 48 hours at −18°C kills all stages of wax moth (eggs, larvae, pupae). Freeze frames before storage; store in sealed plastic bins or bags afterward.
• Light and ventilation: Stack boxes with mesh between them to allow light penetration and airflow. Wax moth larvae avoid light and prefer still air.
• Paradichlorobenzene (moth crystals): Not preferred in organic systems; leaves chemical residue. Avoid or use only as a last resort, and air stored comb for 2 weeks before returning to hive.

Biological Control: Bacillus thuringiensis var. kurstaki (Btk)

Btk is a naturally occurring soil bacterium whose toxin is lethal to moth larvae but harmless to bees, birds, and mammals. Dissolve Btk in water and spray directly on stored comb. Effective for 6–12 months in sealed storage.

Small Hive Beetle

Small hive beetle (Aethina tumida) is native to sub-Saharan Africa but has spread to the Americas, Australia, and parts of Europe. Larvae tunnel through comb, eating honey and pollen, and inoculate honey with a yeast that causes it to ferment and “slime out.”

Identifying an Infestation

• Adult beetles are small (5–7 mm), dark brown to black, hard-shelled, and run quickly when frames are exposed.
• Larvae (white, 10 mm, 3 pairs of small legs near the head) found in comb, fermenting honey pools.
• Fermented honey has a characteristic strong, fruity-sour smell.

Control

Method	Description	Effectiveness
Trap (oil trap)	Small container with vegetable oil placed on the hive floor; beetles fall in and drown	Moderate
Screened bottom board	Beetles fall through mesh; cannot return	Moderate
Strong colony management	Bees herd beetles into corners; keep colonies strong	High (primary strategy)
Soil treatment	Diatomaceous earth or Btk around hive base; targets pupating larvae in soil	Moderate

Small hive beetles pupate in soil outside the hive. In sandy soils, diatomaceous earth (DE) applied within 1 m of the hive entrance reduces pupal survival significantly. Apply after rain, as it loses effectiveness when wet.

Ants

Ants rob honey stores and harass bees, rarely destroying a colony outright but causing significant stress and wax damage.

Physical exclusion methods:

• Leg grease traps: Wrap hive stand legs with a wide band of cloth and coat with petroleum jelly, automotive grease, or sticky trap material. Ants cannot cross sticky or greasy surfaces.
• Tanglefoot rings: Commercial sticky barrier applied to legs or metal bands.
• Water moats: Place hive stand legs in cans of water with a few drops of cooking oil (oil prevents evaporation and reduces mosquito breeding). Ants cannot cross.
• Cinnamon: Sprinkle powdered cinnamon around the hive base; refreshed after each rain. Less effective but chemical-free.

Pest Management Summary

Varroa is the most serious threat to managed colonies worldwide. Monitor monthly with an alcohol wash test and treat whenever mite loads exceed 3%. Oxalic acid vaporization during broodless periods is the most effective chemical-free treatment (95–99% efficacy). Wax moths destroy stored comb but rarely harm strong active colonies — freeze comb before storage or use Btk. Small hive beetles are controlled primarily by maintaining colony strength and using oil traps. Ants are excluded physically with grease or water moats on hive stands. All pest management prioritizes strong colonies and good hive hygiene over chemical intervention.