External bee mite

The external bee mite (Acarapis externus) is a microscopic acarine mite belonging to the Tarsonemidae family. Unlike its relative that infests the tracheal system, this species lives exclusively as an ectoparasite on the outer surface of honey bees.

Adult mites are tiny, measuring approximately 100-150 micrometers in length. They possess a flattened, pale-colored body equipped with specialized claws and suckers that allow them to attach securely to the bee's exoskeleton.

The preferred habitat for these mites is the neck region of the bee, specifically the soft cuticle in the joint between the head and the thorax, where it is easiest to pierce the armor for feeding.

The entire life cycle of Acarapis externus occurs on the host. Adult females lay eggs on the cuticle, and the larvae develop rapidly, feeding on the bee's hemolymph throughout their maturation process.

Transmission between bees occurs through direct contact. In the winter months, when the colony clusters together for warmth, the high density of bees facilitates the rapid spread of the mite population within the hive.

This parasite affects honey bees (Apis mellifera), which are essential pollinators for agriculture. By parasitizing bees, Acarapis externus can indirectly contribute to lower yields of entomophilous crops due to reduced pollinator efficiency.

The mites feed on the hemolymph of the bees, which leads to metabolic stress and a reduction in the life span of individual workers. An infested colony may suffer from a decline in vigor and overall productivity.

The puncture wounds caused by the mites at the neck joint serve as potential entry points for secondary bacterial and fungal pathogens, further complicating the health status of the honey bee colony.

Severely infested colonies may exhibit decreased foraging activity. Since the bees are weakened, they are less capable of collecting enough nectar and pollen, which is detrimental to the survival of the colony during winter.

Although an infestation by Acarapis externus is rarely lethal on its own, it functions as a chronic stressor that weakens the bees, making them more susceptible to other environmental and biological pressures.

Detection of Acarapis externus is extremely difficult without specialized laboratory equipment because the mites are invisible to the naked eye. Field observations alone are insufficient for accurate diagnosis.

Beekeepers might notice general signs of colony weakness, such as sluggish behavior or a decline in the number of foraging bees, though these signs are non-specific and common to many bee health issues.

A definitive diagnosis requires microscopic examination of bee samples. Beekeepers or diagnostic laboratories must dissect the neck area of sampled bees and observe the joints under high magnification to confirm the presence of mites or their eggs.

Because the clinical signs are subtle, the mite often goes unnoticed until the colony health begins to decline significantly. Regular monitoring programs are essential to track the presence of these parasites.

It is important for apiary managers to distinguish this external mite from other internal parasites. Diagnostic protocols often involve sampling older worker bees, as they are more likely to carry higher mite loads.

Management of the external bee mite is usually incorporated into broader integrated pest management (IPM) programs targeting other bee parasites such as Varroa destructor or tracheal mites.

Effective control measures include:

• Application of organic acids, such as formic acid, which have shown efficacy in reducing mite populations within the hive.
• Utilization of approved synthetic acaricide strips that are placed in the brood chamber to target external parasites through contact.
• Implementing strict quarantine practices when introducing new colonies or bees to the apiary to prevent the introduction of new parasite strains.

Maintaining optimal hive conditions, including good ventilation and healthy nutrition, can enhance the natural resilience of the bees against various stressors, including mite infestations.

Selective breeding programs aimed at developing mite-resistant or tolerant bee stocks represent a long-term strategy to reduce dependency on chemical treatments within the beekeeping industry.

All chemical treatments must be performed in accordance with regional regulations and product labels to ensure the safety of the bee colony and the quality of the honey produced.