An Overview of Varroa Control
Varroa mites are present in every honey bee colony.
Adequate varroa control is a tool to reduce colony losses.
Each method of varroa control has a variable efficacy, depending on in-hive conditions.
Generally, a combination of control methods appears to be the most effective for year-round infestation pressure.
How Varroa Affects the Colony
Varroa mites feed on an important organ in developing brood called the fat body. This alters the expression of genes related to stress response, immunity, nervous system function, metabolism, and behavioral maturation.
Varroa mites host a litany of diseases that they pass onto the bees. One of the most visually obvious is Deformed Wing Virus (DWV). In general, the presence of any malformed bees at any time should ring alarm bells to initiate varroa control.
How and Why to Sample Mites
Varroa treatments are pesticides (even the natural ones). By taking a needs-based approach, a beekeeper reduces unnecessary exposure to their bees, and reduces the accumulation of harmful residues in wax and honey.
Varroa mites can be sampled in three ways: measuring natural mite fall onto a sticky board, performing an alcohol wash, or counting reproducing mites in pupa cells.
Bees can and will develop natural resistances to varroa mites. Working to support this process is called Darwinian beekeeping. The focus of this approach is primarily on tolerance for the mite and not on gentleness, production of honey, or any other traits important for the beekeeper and bees. Selection must still be done, whether based on mite counts or colony vitality. Colonies that do not meet the selection criterion must be moved and treated, or culled.
Integrated Pest Management: An Ounce of Prevention
Choose an apiary site with good sun and drainage.
Reduce drifting and robbing by spacing colonies out, making them visually distinct from each other, and keeping entrances small.
Develop a sanitary routine.
Varroa are relatively safe from most mite controls while they are reproducing inside of capped brood cells. Thus, a beekeeper can take advantage of biology to find the most efficient opportunities to completely eradicate mites from colonies. This maximizes efficacy.
Timing is Important
Varroa strongly prefer drone brood. Thus, drone brood can be regularly removed, significantly reducing the bee:mite ratio in the colony. However, this is, essentially, castration; it it important to let the best hive(s) continue to produce drones during nectar flows, for selective reproduction.
In both an artificial or natural swarm, it takes nine days for the brood produced to be capped. Treatment should be applied during this period.
If immediate action if required, all capped brood may be removed from a colony.
Queen Confinement and Comb Trapping
To obtain a brood-free colony, a queen may be caged until all brood has emerged (25 days) and treatment may then be applied in the nine days before new brood is capped again.
Alternately, a queen may be restricted to a single frame via laying cage for eight days. Then, the queen is given a fresh frame to fill and the open brood frame is placed beside it to catch mites. This is repeated three times. Each time a frame with eggs/larvae is replaced, the oldest frame is removed and frozen. In the end, the colony is totally brood free, and most of the mites are caught in the capped frames.
Proven Combinations
Spring
Remove drone brood.
Due to the high amount of honey, wax, and brood being produced during this period, treatment should be minimized.
Perform splits when possible, and treat queenless split colonies when they are free of capped brood.
Treat wild swarms within eight days of capture to avoid introducing pests to the apiary.
Summer
Remove drone brood.
Perform splits when possible, and treat queenless split colonies when they are free of capped brood.
Treat wild swarms within the eight days of capture to avoid introducing pests to the apiary.
After the main honey flows, take advantage of the dearth in August by confining queens or comb trapping.
Fall
Remove drone brood.
Treat wild swarms within eight days of capture to avoid introducing pests to the apiary.
Following the Brazilian pepper flow in October, colonies with high mite loads should be rendered broodless and treated.
Once temperatures begin to drop, beekeepers have the most flexibility of choice between treatments.
Treatment Options: A Pound of Cure
It is important to understand how a pesticide works. Always read the label. Additional protective gear may be required for safe application.
Using the same products repeatedly causes resistance.
