Tropilaelaps is a parasitic mite (class Arachnidae), native to Asia, where it parasitizes colonies of Apis dorsata, the giant honey bee. There are four species in this genus: T. koenigerum, T. thaii, T. clareae and T. mercedeseae. All of these species are located in tropical and subtropical areas of Asia. The last two are susceptible to parasitizing A. mellifera (OIE 2019). In fact, this parasitization has been confirmed in countries where both species of bees coexist, such as Afghanistan, South Korea, China or the Philippines (Delfinado, 1961). It is necessary to pay attention to imports of live beekeeping stuff since they are considered a risk for global beekeeping, as has happened with Varroa destructor.

Parasite characteristics:

The mite is small and can be confused with varroa due to its color and size, although its body is elongated longitudinally, instead of transversely like varroa, and they are somewhat smaller, 1 mm long by 0.6 mm wide. They are reddish color and have four pairs of legs. Males are slightly smaller than females and the exoskeleton is less sclerotized. They run through the brood areas at great speed, so to detect them a visual acuity and attention is needed.

In many aspects, the life cycle of Tropilaelaps is very similar to that of varroa, where one or several (up to 12, OIE 2019) fertilized females enter the larva cell shortly before being capped. Each female lays between 3-4 eggs per cell (OIE, 2019; Ritter, 2014), there are usually one male and the rest, females, mite’s development period to maturity lasts only 6-7 days, much shorter than varroa. They mainly parasitize the brood, preferring drones, whose entire cells can be affected. Their phoretic phase is truly short, only 1-2 days (Burgett, 1983), although adults cannot feed, they can survive up to 5-10 days; a fertilized female must lay eggs within 48 hours. This explains why in an infestation of the hive they a faster development have than varroa, for this reason in an infection of both mites, a dominance of T. clareae over V. destructor has been observed. When both species of mites parasitize the same larva, the reproductive capacity of both is impaired.

This mite not only feeds on capped larvae but also on still juvenile larvae. Tropilaelaps can also mate outside the larva cell (Chantawannakul 2018). The way they feed is somewhat different from varroa, producing multiple small wounds through which they feed on the bee’s hemolymph (Phokasem, 2019). It can also act as a vector for viral diseases such as DWV (Forsgren, 2009).

Figure. Varroa on the left, compared with Tropilaelaps on the right. Photograph by Zachary Huang, www.beetography.com.

Symptoms of the disease

Infestation by Tropilaelaps mite can cause the death of up to 50% of the larvae, macroscopically shown in the comb as irregular brood pattern. Some dead bees half emerged from the cells, adult bees with deformities in wings, antennae, and legs, sunken abdomens (Vidal-Naquet, 2015) and bees crawling towards a spout (Atwal and Goyal, 1971) and perforated opercula.

Parasitized bees have a lower weight and die much earlier, also due to the viral load (Khongphinitbunjong, 2016). There is general depopulation in the colony. Colonies could collapse, others abscond, taking the mites to new locations.

Diagnosis

Examination of the brood of drones and workers, uncapping cells and tapping the frame on a tray where the mites fall (bump test) and are the main diagnostic steps for the detection of mites. They can also be seen on the sticky board covered with a mesh.

Other monitoring methods that can also be used is washing workers with water and alcohol or soapy water and checking for the presence of mites. Mites can be seen with the naked eye or with a magnifying glass.

Treatment

Taking advantage of the experience with varroa, different treatments were tested on Tropilaelaps. As for varroa mites, integrated pest management have given good results, using both medicinal and biotechnical methods.

Among those that worked, formic acid and splitting colonies to break the brood cycle worked well, while amitraz did not, since it requires longer contact time between treatment and the bee and Tropilaelaps has a phoretic phase that is too short for the treatment to be effective. 

Inducing a brook break seems to be the most effective method by queen caging, since without brood the mites die of starvation in a short time (Guzmán, 2017). It is worth thinking that in temperate climates where there is no winter break and there is practically always breeding, parasitization could be difficult to control (Anderson, 2013).

Final thoughts

Tropilaelaps is another of those parasitic species with a localized distribution in areas of Asia with a tropical and sub-tropical climate. Several species of this genus have shown to be able to make the jump between their host species, Apis dorsata, and parasitize a new host, Apis mellifera. The effect of global warming and merchandise exchanges make Tropilaelaps a certain risk for global beekeeping and this has been expressed by the scientific community, demanding more specific research on this parasitic species (Anderson and Roberts, 2013; Chantawannakul, 2018).

In my case, I have been able to attend lectures by British researchers who have traveled to the Philippines to learn, investigate, and disseminate knowledge in order to quickly identify any possible entry of the parasite into the European continent. Seeing how new diseases are leaving their local area and finding a foothold in other regions with similar climates, it seems most sensible to start becoming familiar with these mites.

References :

  1. Delfinado, MD and Baker, EW(1961). Tropilaelaps, a new species of mite from the Philippines (Laelapidae [s.lat]: Acarina). Fieldiana Zoology, 44, 53–56.
  2. Ritter, W. (ed) (2014) Bee Health and Veterinarians. Paris, Fr: WOAH. 
  3. OIE (2008) Tropilaelaps mites. Office International des Epizooties (OIE) Manual Chapter 2.2.6.
  4. BURGETT M., AKRATANAKUL P. & MORSE R.A. (1983). Tropilaelaps clareae: a parasite of honeybees in south-east Asia. Bee World, 64, 25–28.
  5. Chantawannakul, P., Ramsey, S., vanEngelsdorp, d. et al. (2018). Tropilaelaps mite: an emerging threat to European honey bee. Current Opinion in Insect Science 26: 69-75
  6. Phokasem, P., de Guzman, L.i., Khongphinitbunjong, K. et al. (2019). Feeding by Tropilaelaps mercedeseae on pre- and post-capped brood increases damage to Apis mellifera colonies. Scientific Reports 9: 13044.
  7. FORSGREN E., DE MIRANDA J. R., ISAKSSON M., WEI S., & FRIES I. (2009). Deformed wing virus associated with Tropilaelaps mercedesae infesting European honey bees (Apis mellifera). Exp. Appl. Acarol., 47, 87–97
  8. Vidal-Naquet, N. (2015). Honeybee Veterinary Medicine: Apis mellifera L. Sheffield, UK: 5m Publishing 
  9. ATWAL A.S. & GOYAL N.P. (1971). Infestations of honeybee colonies with Tropilaelaps, and its control. J. Apic. Res., 10, 137–142.
  10. KHONGPHINITBUNJONG K., NEUMANN P., CHANTAWANNAKUL P. & WILLIAMS G.R. (2016). The ectoparasitic mite Tropilaelaps mercedesae reduces western honey bee, Apis mellifera, longevity and emergence weight, and promotes Deformed wing virus infections. J. Invertebr. Pathol., 137, 38–42.
  11. DE GUZMAN L.I., WILLIAMS G.R., KHONGPHINITBUNJONG K.& CHANTAWANNAKU P. (2017). Ecology, life history, and management of Tropilaelaps Mites. J. Econ. Entomol., 110, 319–332.
  12. ANDERSON D.L. & ROBERTS J.M.K. (2013). Standard methods forTropilaelaps mites research. In: The COLOSS BEEBOOK, Volume II: Standard methods for Apis mellifera pest and pathogen research, Dietemann V., Ellis J.D., Neumann P., eds. J. Apicultural Res., 52, http://dx.doi.org/10.3896/IBRA.1.52.4.21.
  13. National Library of Medecine, Taxonomy Database.

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