4.1. Morphological methods

Morphological analyses are best carried out on mite specimens that have been cleared of their body tissue and mounted on glass microscope slides. Methods for clearing and mounting Tropilaelaps mites are the same as those described for Varroa mites (Dietemann et al., 2013). Generally these specimens have been previously collected and stored in alcohol. However, sometimes it helps to collect specimens that are destined for morphological analyses into hot water before they are transferred in alcohol. This relaxes their internal body tissues and exposed hard-to-see organs, such as chelicerae, which are normally hard to see in mounted specimens that have simply been collected into alcohol.

Identification of specimens to the species level using morphology can be troublesome. Hence, the starting-point for identifying them should always be from information known about the location and host bee from which they were collected. Mites found on either giant Asian honey bees or European honey bees in the Philippines (except on Palawan Island) will in all probability be T. clareae, whereas those found on European honey bees in other parts of Asia (and Melanesia) will be T. mercedesae. The two other species, T. koenigerum and T. thaii, have been found only on their native Asian bee hosts, A. dorsata, and A. laboriosa respectively.

Many of the physical characters used to identify mites (such as their body size, sensilli and structures on body plates) are highly variable within the genus and even among member of the same species (Anderson and Morgan 2007). A key for identifying the different species of Tropilaelaps is given in Table 1.

The 4 main physical characters most useful for identifying Tropilaelaps mites to the species levels are:

  1. Body length.
    T. koenigerum is the smallest member of the genus with a body length of < 700 µm for females and ~575 µm for males. Female T. mercedesae, T. clareae and T. thaii are much longer at ~ 950-990 µm, ~870-885 µm and ~ 890 µm respectively, while the body lengths of male T. mercedesae and T. clareae are slightly smaller than their respective females at 907-927 µm and 852-858 µm, respectively. Males of T. thaii have yet to be discovered.
  2. Shape of the anal plate.
    Male and female T. koenigerum have a distinct pear-shaped anal plate, female T. Thaii have a bell-shaped anal plate, while the anal plates of male and female T. mercedesae and T. clareae are highly variable and of little use as a taxonomic reference.
  3. Structure of the male sperm transfer organ (chela spermatodactyl or spermadactyl).
    Males of T. koenigerum have a ‘pig-tail’ loop at the apex of the chela spermatodactyl, while the apex of the chela spermatodactyls of male T. mercedesae and T. clareae are long cork-screw-like structures (Fig. 4).
  4. Placement and shape of teeth on female chelicerae.
    Female T. koenigerum have a single sub apical tooth on the chelicerae with a characteristic groove near its anterior base, whereas T. mercedesae and T. clareae females also have the sub apical tooth, but without the groove. Female T. thaii lack the sub apical tooth (Fig. 6).

 

Table 1. Key to identification of Tropilaelaps mites. Males of T. thaii have not been discovered, but this species is restricted to A. laboriosa.

1. a. Collection sites:             

       The Philippines (except
       Palawan Island) and Sulawesi Island (in Indonesia).

1. b. Collection sites:
        All other localities (including
        Palawan Island)

Tropilaelaps clareae
Parasitizes Apis breviligula and Apis mellifera in the Philippines and Apis dorsata binghami and Apis mellifera in Sulawesi.

2

2. a. Body length:
         ≤ 700 µm.

Tropilaelaps koenigerum
Primarily found parasitizing A dorsata dorsata in mainland Asia.


    b. Body length:
         ≥ 840 µm


3.

3. a. Female chelicerae:
         No apical tooth.


     b. Female chelicerae:
         One apical tooth present

Tropilaelaps thaii
Parasitizes Apis laboriosa in mountainous regions of mainland Asia.

Tropilaelaps mercedesae
Primarily parasitizes Apis dorsata dorsata and Apis mellifera in mainland and southeast Asia.

 

Fig. 6. Comparisons of female chelicerae of T. clareae (TC), T. mercedesae TM), T. koenigerum (TK) and T. thaii (TT) (light microscopy, x800). Photo: Denis Anderson.

figure06