3.1. Mite appearance
Adult Tropilaelaps mites are small (<1 mm long), light brown, and hold their first pair of legs upright, resembling antennae (Fig. 1). They can often be seen moving quickly over the surface of combs in infested colonies. Their body shape is quite different from that of Varroa mites, being much longer than it is wider (Fig. 2).
There are clear morphological differences between the sexes of the different species. Males of T. thaii have not yet been discovered. Males of T. mercedesae, T. clareae and T. koenigerum are slightly smaller than their female counterparts and their epigynial thoracic plates are also shorter and sharply pointed toward their posterior end (Fig. 3). In any collection of Tropilaelaps mites, males are usually much less common than females (Rath et al., 1991; Anderson and Morgan 2007). Males can be easily identified in the field using a magnifying glass to observe the chela spermatodactyl (sperm transfer organ), which in T. mercedesae and T. clareae is long with a spirally coiled apex and in T. koenigerum is short with a ‘pig-tail’ loop at its apex (Fig. 4).
The nymph stages of Tropilaelaps are brilliant white and are easily observed with the
naked eye (Fig. 5).
Fig. 1. A gravid T. mercedesae adult female feeding on an A. mellifera pupa. Note the first pair of legs of the mite is held upright, resembling antennae. Photo: Denis Anderson.
Fig. 2. Comparisons of a female T. mercedesae (left) with two female V. jacobsoni (right) on an A. mellifera larva. Photo: Denis Anderson.
Fig. 3. Comparison of mounted specimens of a T. mercedesae male (top) and female (bottom). Anterior arrow on male points to the corkscrew like spermodactyl (sperm transfer organ) and posterior arrow points at the non-overlapping epigynial thoracic plate. Bars = 0.1 mm. Photo: Denis Anderson.
Fig. 4. Scanning electron micrographs of the sperm transfer organs of male T. clareae (left) and T. koenigerum (right). Bar = 10µm. Photo: Denis Anderson.
Fig. 5. A family of mites (T. mercedesae) with mother mite (light brown) and different stages of offspring (white) at the bottom of a cell from which the honey bee pupa was removed. Photo: Denis Anderson.