3.3.2. Screening individual bees

When the level of infestation is low, tracheae from an individual bee need to be examined. Bees may be anesthetized or killed by freezing before examination.  Milne (1948) developed a technique to locate the internal mites on individual bees (see Figs. 10 and 11 for details).

  1. The bee is placed under a dissecting microscope, held prone with forceps (across abdomen) and the head and the first pair of legs is scraped off using a scalpel or razor blade.
  2. The ring of prothoracic sclerite (collar) is also removed using a fine forceps.
  3. The exposed tracheae of both sides are removed after carefully detaching them from the thoracic wall.
  4. The tracheae are removed and placed on a glass slide and examined under a microscope for mites; this technique is very time-consuming and also has the possibility to lose mites while separating tracheae from the thoracic wall and transferring them to the slide.
  5. Lorenzen and Gary (1986) modified this technique where the thoracic tergite was removed as a flap to look at mites in situ (see also Ritter et al., 2013).

Liu (1995) developed a rapid technique to distinguish live mites from dead by staining with thiazolyl blue tetrazolium, which stains the live mites purple. The tracheae, after mounting on glass slides, are perfused with thiazolyl blue tetrazolium solution (5 mg stain in 5 ml distilled water). The cuticle of live mites picks up the stain immediately and turns purple, dead mites turn greenish yellow.

Fig. 10. Dissecting a bee to determine tracheal mite infestation. A. Pin a worker bee through the thorax using two insect pins (the bee’s body will pivot in the dish if pinned with only 1 pin). The bee in this figure is pinned into a petri dish of hardened beeswax. The bee is covered in 70% ethanol to facilitate dissection. B. Remove the abdomen. This is a helpful technique to limit contents from the bee’s digestive systems from emptying into the field of view. C. Remove the head and front pair of legs. The “collar” junction is arrowed. D. The beginning of collar removal. The area where the collar has been removed is arrowed. E. The collar has been removed, including the part that covers the spiracles (arrowed). The bee’s right trachea (the one on the left in the figure) is outlined to show shape and position. F. Trachea infested with mites (on left, arrowed) and not infested with mites (on right, arrowed). G. Close-up of infested trachea and H. close-up of uninfested trachea. Photos: Lyle Buss and Tricia Toth, University of Florida, USA.


Fig. 11.
Mites seen through tracheal tube. Light Microscope photo: L de Guzman, 140x).