Related Topic: Honey Bee Parasites, Pests and Predators - New slide set, viewable on Web

The mite Varroa jacobsoni can be found on adult bees, on the brood, and in hive debris. The most severe parasitism occurs on the older larvae and pupae, with drone brood being preferred to worker brood (Ritter and Ruttner 1980). In heavy infestations, pupae may not develop into adult bees. The adults that do emerge may have shortened abdomens, misshapen wings, and deformed legs and may weigh less than healthy bees (De Jong et al. 1982).

The adult female mite is oval and flat, about 1.1 mm long and 1.5 mm wide, and pale to reddish brown; it can easily be seen with the unaided eye. The mites attach to the adult bee between the abdominal segments or between body regions (head, thorax, abdomen) and are therefore difficult to detect. However, they can be easily recognized against the white surface of pupae. Male mites are considerably smaller and are pale to light tan (Delfinado-Baker 1984).

It is important to note that the bee-louse, Braula coeca, resembles Varroa jacobsoni in size and color. However, Braula, being an insect, has six legs that extend to the side. Varroa, an arachnid, has eight legs that extend forward.

When sampling, remember that the number and location of mites in a colony vary according to time of year. The number of mites is lowest in spring, increases during summer, and is highest in fall. During spring and summer, most mites are found on the brood (especially drone brood). In late fall and winter, most mites are attached to adult worker bees.

Methods of Examining Adult Honey Bees

For a sample of adult honey bees, 500 to 1000 bees should be collected. This can be done by brushing honey bees off the comb through a large-mouthed funnel (of paper or cardboard, etc.) into a container or by using a modified portable car vacuum cleaner. Individual honey bees can be examined with or without the aid of a hand lens or a dissecting microscope. When the mites are moving about on a bee, they are fairly easy to detect; but once they attach themselves between segments, they are difficult to find. Mites can be detected and collected by three methods, as follows:

Shaking Method

Varroa jacobsoni can be dislodged by shaking the bees in liquids such as hot water, alcohol, detergent solution, hexane, gasoline, or diesel fuel. We recommend 70% alcohol (ethyl or isopropyl) because some of the other materials are dangerous or difficult to use. The alcohol kills and preserves the bees for other purposes, such as examination for Acarapis woodi. De Jong et al. (1982) found that hand-shaking bees in alcohol for 1 minute dislodged about 90% of the mites and that mechanical shaking on a rotary shaker for 30 minutes removed 100% of the mites. The mites are collected by passing the bees and alcohol through a wire screen (8- to 12- mesh) to remove the bees and then sieving the alcohol through a 50-mesh screen or cotton cloth. The screen or cloth is then examined for mites.

Ether Method

This technique is a rapid and efficient detection method in the field and avoids the handling, shipping, and time-consuming procedures associated with shaking adult bees in alcohol or other solvents. The bees (500-1,000) are collected in a jar and anesthetized with ether delivered from an aerosol can (this aerosol product is sold in auto-parts stores as an aid to start engines). A 1- to 2-second burst of material is adequate. The bees are then rotated in the jar for about 10 seconds. The majority of mites will have dislodged from their hosts and should be adhering to the inside wall of the jar. To complete the process, the bee sample is deposited on a white surface and spread around. This should cause any remaining mites to fall onto the white substrate. The bees should be examined immediately after the application of ether because the mites tend to stick to the bees if left in the jar for more than a few minutes. Alternatively, the bees can be left in the jar to which alcohol is added for laboratory shaking and preservation.

Heating Method

Live adult honey bees can be shaken into a wire-based cage and placed in an oven over white paper. The bees are heated for 10-15 minutes at 46 degrees - 47 degrees C. Then Varroa jacobsoni, if present, can be observed on the white paper (Crane 1978).

Methods of Examining Brood

To look for mites on brood, the pupae (preferably drone) are examined. Varroa jacobsoni can be easily seen against the white surface of worker or drone pupae after they are removed from their cells. It is suggested that a minimum of 100 drone pupae per colony be examined. The pupae can be collected by one of the following methods:

* The classic method of pupal collection is to uncap each cell and then remove the pupae with forceps or a hive tool.

* Groups of pupae can be quickly and easily removed from their cells by inserting a capping scratcher at an angle through the cappings and lifting the brood and cappings upward (Szabo 1989).

* With a long-bladed knife, the caps are sliced off an area of brood 4-6 square inches. The comb (frame) is then sharply jarred on a hard, flat, white surface such as a hive top. The brood will fall onto the white surface, and the mites can be easily observed.

* The brood comb can be incubated at 37 degrees C, followed by examination of all the emerged bees and remaining brood.

Methods of Inspecting Hive Debris

Debris in a hive (such as wax particles, pollen, dead bees and brood, and mites) normally falls to the hive floor and is removed by house-cleaning bees during warm weather. This material can be collected and examined for the presence of Varroa jacobsoni as follows:

* The collection of hive debris can be facilitated by white construction paper on the hive floor. The paper is stapled under a wood (1/4-inch) and wire (8- to 12-mesh) frame, which protects the paper and debris from the bees. The paper is examined for mites, which can be easily seen against the white background. A magnifying glass or dissecting microscope can be helpful in locating the mites in the debris. Sticky boards or shelf paper (with the adhesive surface exposed) instead of construction paper will help hold the debris.

* The acaricides used to treat mite infestations can also be applied to bee colonies in combination with the paper method to detect Varroa jacobsoni. Apistan is currently approved and available for this purpose. After treatment, the mites drop to the paper and can be easily detected. It is important that the paper have a sticky surface (see previous paragraph) to hold any recovering mites.

* A flotation method can be used to examine debris for Varroa jacobsoni. Hive debris is placed in a jar or pan and covered with 98% alcohol. The mites float to the surface while the heavier debris sinks (Ritter and Ruttner 1980).

* Mites can sometimes be collected in dead bee or pollen traps attached to the colonies.

Related Topic: Honey Bee Parasites, Pests and Predators - New slide set, viewable on Web