Honey Bee Tracheal Mite

The honey bee tracheal mite, Acarapis woodi (Rennie) is an internal parasite that infests the respiratory system of adult honey bees. This mite is responsible for causing acarine disease or acariosis. The western honey bee (Apis mellifera), the Africanized honey bee (Apis mellifera scutellata), and the eastern honey bee (Apis cerana) are the only known hosts of this pest. Drones, workers, and queens may be infected.

Geographical Distribution

This mite was first reported in 1921 on the Isle of Wight in the English Channel and was originally believed to be the cause of Isle of Wight disease, which caused heavy losses in hives. The Honey Bee Act of 1922 was enacted by Congress primarily to prevent importing live honey bees infested with the mite into the United States.

Before 1980, the mite was never found in North America. In 1980, however, the mite was isolated from adult honey bees in Mexico, about 200 miles from the United States border. From 1980-82, the USDA Bioenvironmental Bee Laboratory at Beltsville, Maryland, in cooperation with the Animal and Plant Health Inspection Service (APHIS), conducted a survey of apiaries in the United States for mites of honey bees. The tracheal mite was not found in bee samples collected from 4,400 apiaries.

The honey bee tracheal mite was first detected in the United States on July 3, 1984, in a commercial beekeeping operation in Weslaco, Texas. Tracheal mites are now widely distributed throughout the United States. The rapid spread of the mite in North America can be traced through the movement of migratory beekeepers, sale of queens, packages, and nucleus colonies (nucs). Within the first 13 months of discovery, the mite was found in 17 states, which illustrates the mobility of beekeeping in the United States.

Description

Both female and male mites are whitish in color and microscopic in size. Females are .004-.007 inches (143-174 microns in length and 77-81 microns in width) and males .003-.005 inches (125-136 microns in length and 60-77 microns in width). The body is oval, widest between the second and third pairs of legs, with a shining smooth cuticle. A few long fine hairs are present on the body and legs. It has elongated, beaklike mouthparts for active feeding on the host.

General Biology and Life Cycle

The entire mite life cycle is spent within the trachea or breathing tubes in the thorax of adult honey bees except for brief migratory periods. Mites are also occasionally found in air sacs in the thorax and abdomen. Within the trachea, the mite reproduces and feeds. Mites penetrate the breathing tubes with their mouthparts and feed on blood. Normal thoracic tracheae are clear, colorless, or pale amber. Infested tracheae deteriorate progressively and show patchy discoloration. In a slight infestation, one or both tracheal tubes contain a few adult mites and eggs that can be detected near the spiracular openings (breathing pores). At this stage, the tracheae may appear clear, cloudy, or slightly discolored. The tracheae of severely infested bees have brown blotches, with brown scabs or crustlike lesions, or they may appear completely black, and are obstructed by numerous mites in different stages of development, as well as mite debris. Trachea that are normally elastic and flexible become stiff and brittle. Discoloration and atrophy of flight muscles may also occur. As a result of mite feeding, the blood of infested bees has a higher than normal bacterial count.

Within 24 hours after worker bees emerge from their cells, female mites migrate into their trachea by passing through the first thoracic spiracle and remain there for life's duration or until their host dies. Each female mite lays 5 to 7 eggs within 3 or 4 days after entering the trachea and continues to lay eggs throughout her life. The eggs require 3 to 4 days to hatch. The life cycle consists of an egg, larva, resting stage, and adult male or female. The males are mature after 11 to 12 days and the females on the 14th or 15th day. All stages of the mite may be found in older bees. The highest number of mites per bee is attained in bees 11-12 days old, and the mite population declines in bees more than 21 days old.

Mites are spread within the colony as a result of bee-to-bee contact. Mated female mites leave the breathing tubes where they developed and climb to the tip of a body hair. As bees come in contact with one another, the mites attach themselves to the hairs of a passing bee and enter the tracheae through the thoracic spiracles. If the mite does not locate a new host within 24 hours, it will die. Mites leave the tracheae after the death of the bee. Drifting bees between hives and swarms from infested colonies are ways that the mite can be spread within the apiary and between apiaries.

Host Susceptibility to the Mite

Large variations in susceptibility to infestation among U. S. bee stocks have been found. Worker bees become rapidly less susceptible to infestation as they age, and bees more than 9 days old rarely become infested. Gravid female mites (females with mature eggs) migrate preferentially to young bees less than 4 days old, and newly emerged bees, less than 24 hours old, are especially attractive. Queen honey bees also exhibit a rapid decline in susceptibility to mite infestation with increasing age.

Economic Damage

Acarine disease can persist in a colony for years, causing little damage, but combined with other diseases, unfavorable conditions, scarcity of pollen and/or a poor foraging season, the disease can contribute to the death of a colony. Heavy mite infestations are most likely after seasons of poor honey yields and in situations when brood rearing is suppressed during the summer.

The foraging activity of worker honey bees at the hive entrance has been measured and used to study the effects of infestation by tracheal mites. No significant differences were found between infested and noninfested bees for the number of foraging trips, frequency of foraging trips, round trip times, frequency of pollen collection, or time between foraging trips. Nectar loads collected by forager honey bees infested with mites were compared with loads collected by noninfested foragers. The difference in mean honey sac volumes was not significant. Survival of worker bees as a function of mite infestation was determined by comparing, during a 6-week period, the ratio of infested to noninfested bees in subpopulations that were aged in common colonies. Stable infestation ratios throughout the experiment indicated no significant reduction in survival because of infestation. These results strongly indicate that mite infestations do not have a detectable economic effect on colonies when brood rearing is active and honey production is underway.

When the infestation is light or in its early stages, the bees behave as if not adversely affected. Infestation levels tend to decline in colonies when they are actively foraging. Colonies rarely show signs of infestation in summer or fall. Even the relatively few colonies with a large population of infested individuals in spring contain very few infested bees after a good season. The old infested bees from which mites are migrating are busy foraging during a nectar flow, so they become separated from the young susceptible bees and prevent most migrating mites from finding suitable new hosts.

Acarine disease shortens the lives of adult bees, affects flight efficiency, and causes a large number of crawling bees that are unable to fly. In extreme cases, colony populations often dwindle and, ultimately, the colony dies. Infested colonies may not develop normally and may exhibit symptoms of dysentery and exhibit an excessive swarming tendency. Often, however, severely infested colonies appear normal until their death during the winter. Colonies are most affected during winter confinement and early spring as with other stress diseases. Mite infestations are at a maximum in the early spring when the population is comprised of primarily older bees. Only old and heavily infested honey bees are killed by the mite. Whole colonies that have more than 30 percent of the individuals infested are often destroyed during late winter.

Diagnosis

Detection of a tracheal mite infestation is difficult since there are no obvious outward signs of the disease. Accurate diagnosis can be done only by examination of the tracheae for the presence of the mites, which requires a delicate dissection and magnification of 100-250 times.

Control

Many chemicals have been developed and tested for the control of tracheal mites in Europe. To date, only menthol crystals are currently approved in the United States.

Menthol is a crystalline alcohol obtained from oil of peppermint that is commonly used for odor and cooling properties in items such as candies, cigarettes, and shaving creams. Menthol crystals start to evaporate at about 70 °F and will melt to a liquid at 102-105 °F. The vapors are heavier than air, and the best evaporation rate for menthol is between 80 and 85 °F.

Menthol crystals were first approved in the United States for the control of tracheal mites in January 1989. The effectiveness of menthol treatments depends on temperature, formulation (crystals or pellets), dosage, colony size, condition of equipment, position within the hive, and exposure time. Crystals are normally placed in 7-inch square plastic screen packets, with the mesh size small enough to keep the crystals inside. Each packet should contain 50 grams (1.8 ounces) of crystals. A rounded one-third measuring cup is very close to the 1.8 ounce amount. When daily temperatures are 60 °F or less, these packets should be placed on the top bars. If the temperature reaches 80 °F, the packets should be on the bottom board. Placement of the packets on the top bars when it is too warm outside may drive the bees out of the hive.

Menthol is a fumigant and must change from a solid crystal state to a gas to be effective. Replace the packets with fresh packets as needed to maintain menthol in the hive. Do not use menthol during surplus honey flow periods. Remove packets at least 1 month before the beginning of a surplus honey flow to prevent contamination of marketable honey. Ten to twelve weeks after the initial treatment, remove all menthol packets from the hive. The use of menthol in a manner not described above or in areas where there is not a break in the brood rearing cycle may result in reduced honey production or other adverse effects.

Warning

Beekeepers should briefly vent treated hives before working the bees. As with all pesticides, it is a violation of Federal and State laws to use menthol in a manner that is inconsistent with the label. A copy of the label must be in the possession of the beekeeper at the time the menthol is applied. Menthol used improperly can be hazardous to humans and domestic animals. It causes irreversible eye damage. It is harmful or fatal if swallowed. Do not get in eyes, on skin, or on clothing. Wear goggles and chemical-resistant gloves. Wash thoroughly with soap and water after handling. Remove contaminated clothing and wash before reuse.

If swallowed: call a physician or Poison Control Center immediately. Do not give anything by mouth or induce vomiting to an unconscious person.

If inhaled: remove victim to fresh air. Apply artificial respiration if needed.

If on skin: remove contaminated clothing and wash affected area with soap and water. Get medical attention if irritation persists.

If in eyes: flush eyes with plenty of water for 15 minutes. Call a physician immediately.

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Publication 1753
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. Ronald A. Brown, Director