Lesson 63: Tracheal Mites

A microscopic mite that lives inside bees' breathing tubes

The honey bee tracheal mite (Acarapis woodi) is the "other" mite. Unlike varroa, it's too small to see: it lives inside the breathing tubes (tracheae) of adult bees. It was first found in the United States in 1984 and caused heavy colony losses in the years that followed. Today varroa gets most of the attention, but tracheal mites are still worth knowing, especially when a colony dwindles over winter and early spring for no obvious reason.

How it lives

• The mites infest young adult bees, preferring bees less than about four days old.
• Drawn by the bee's breath, a mite enters a breathing hole (spiracle) on the thorax and moves into the trachea.
• There it punctures the tube wall and feeds on the bee's blood (hemolymph), and lives, mates and lays eggs. The mites and eggs plug the tubes, so the bee can't get enough oxygen. The feeding wounds also let in germs. Mites sometimes spread into air sacs in the thorax, abdomen and head.
• Mites pass from bee to bee inside the colony, and to other colonies by drifting and robbing bees.
• Levels are highest in winter and spring.

What it does

Sources differ on how serious it is. Georgia's Bee Program says tracheal mites caused the loss of tens of thousands of colonies after they arrived; an older University of Florida profile says later research found them less serious than first thought, doing the most harm in combination with other problems. Either way, heavy infestations hurt colonies:

• Infested bees live shorter lives (by a few days, in one estimate).
• When more than about 30% of bees are infested, honey production can drop.
• The more bees are infested, the less likely the colony is to survive the winter. Severe infestations usually build up in late summer, and those colonies often die in late winter. In late stages, colonies may abandon the hive (abscond).

The signs

The signs look a lot like Nosema (lesson 61) and some viruses (lesson 62), so you can't diagnose tracheal mites by eye: - Weak bees crawling on the ground in front of the hive, climbing blades of grass and falling back. - Bees that can't fly, with wings held apart at odd angles ("K-wing", where all four wings show). - Sometimes swollen abdomens. - A colony that dwindles in winter or early spring.

Confirming it

A lab looks for the mites by dissecting bees under a microscope. Healthy breathing tubes are clear and pale; infested ones show dark blotches and scarring. To get a sample checked, put bees in alcohol (lesson 40) and contact your county Extension office or a diagnostic lab.

Managing tracheal mites

• Keep colonies strong and free of other stresses.
• Resistant stock: bees differ genetically in how well they resist tracheal mites (some bee strains show resistance). If a colony has trouble, requeening with stock from a breeder who selects for mite resistance is a good step (lessons 45, 83).
• Grease (oil) patties: a traditional, low-risk method. Mix two parts sugar with one part vegetable shortening, make a patty about 4 inches across, sandwich it between wax paper, trim the edges so bees can reach it, and lay it on the top bars of the brood box. Bees pick up oil on their bodies, which makes it hard for mites to find a young bee to move onto. It doesn't contaminate honey, so it can stay on for a long time.
• Menthol: special menthol products for tracheal mites are sold by bee suppliers. They only work above about 60°F, and must be removed before a nectar flow so they don't taint the honey. Use only a product registered for this use, and follow its label exactly (lesson 57).

What to remember

• Tracheal mites are microscopic mites inside adult bees' breathing tubes; worst in winter and spring.
• Signs (crawling bees, K-wings, dwindling) look like Nosema. Confirm with a lab.
• Manage with strong colonies, resistant stock / requeening, grease patties, or registered menthol products used per label.

Quick check

1. Where on the bee does the tracheal mite live?
2. Why can't you diagnose tracheal mites from the crawling bees in front of the hive?
3. How does a grease patty help?

Adapted from: UGA Bee Program, Honey Bee Disorders: Honey Bee Parasites; UF/IFAS Extension, Honey Bee Tracheal Mite (Featured Creatures, IN329); Penn State Extension, A Quick Reference Guide to Honey Bee Parasites, Pests, Predators, and Diseases; Delaplane, Honey Bees and Beekeeping (UGA Bulletin 1045, rev. 2017); Shimanuki & Knox, Diagnosis of Honey Bee Diseases (USDA AH-690, rev. 2000).

Adapted from university Extension sources. Experienced Georgia beekeepers are reviewing these lessons. See something that doesn't match your experience? Tell us.