Varroa Predators

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Varroa Predators

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The Predators

Pseudoscorpions

Pseudoscorpions are tiny arthropods (between 2 and 7 mm) of which physiognomy remind strongly of scorpions. They live predominantly in humus or compost, but can also be found in tree bark, bird nests and sand dunes. More than 3000 species are known in the world, of which 100 live in Europe.[1][2] They feed on other small arthropods. They have a phoretic relationship with larger insects, as, e.g., flies or spiders, that is, they use they as a « taxi » to migrate to new territories[2]. The fact that bees interacted with has actually been known before: Weygoldt observed that pseudoscorpions feed as well on mites found on their hosts and that the Chelifer cancroides species was often found in beehives: "Normally the pseudoscorpions do not harm their hosts: they like the warmth of the nests and feed on other animals living there – wax moth or beetle larvae, for example."[2] Moreover, it is allowed to assume that the presence of pseudoscorpions in beehives belong to the "defence mechanisms" or the Asian bee, Apis cerana against the varroa mite.[3] Pseudoscorpions happen to attack their hosts, but this has been observed up to now only in tropical species.[2] Pseudoscorpions seem thus to have simply added varroa to their "menu".

Velvet Mites

Van Dugteren[4] has also observed a velvet mite feeding on a varroa mite in the hive.

The velvet mites (Trombidium holosericeum) belong, as pseudoscorpions, to the pedofauna. The larva parasites larger arthropods[5] nevertheless without harming their hosts.[6] The imago is considered as a useful animal in gardening and agriculture since it is a predator of harmful mites, aphids and small caterpillars.[7] It would thus not be surprising that it would not either despite a varroa.

As Van Dugteren's observation has been an isolated case, it might that it has been an opportunistic caught[8], nevertheless, it would be interesting to study further if the velvet mite could develop as a regular predator of varroa, at least assist the elimination of varroa mites and find a usefulness in beekeeping as in gardening of agriculture.

Efficiency

Different beekeepers around the world, e.g. in South Africa (in 1997), New Zealand[9], the Netherlands (in 2003[4][10]) and Germany have observed that, when important populations of pseudoscorpions were to be found in the vicinity of and in beehives, these beehives were completely free of varroa. Other beekeepers mentioned the standstill of pseudoscorpions activity after a short time.[10]

More studies should be undertaken to determine which conditions are most favourable to pseudoscorpions to help beekeepers reproducing them.

Risks

As pseudoscorpions are cosmopolitan animals, its introduction in beehives should not present any risk from an environmental point of view, with the condition that local species are bred. The velvet mite is also a native species of Europe.


Practicability

Predator Breeding

In organic gardening, predators (particularly ladybird, hoverfly and lacewing larvae) are e.g. used for the control of harmful animals such as aphids: either and preferably the garden will be laid out in a manner that an adequate habitat will be offered to those predators, or, to give it a boost or in case of emergency, it is possible to buy these predators from specialist suppliers. This idea can be transferred to beehives, that is to say, either introducing deliberately varroa predators in beehives, or maintaining a favourable environment to varroa predators in the vicinity of beehives.

This is the solution suggested by Piet van Dugteren[4]. He has observed that pseudoscorpions develop particularly well in compost heaps and maintains since then a heap of dead leaves at the bottom of his hives. Pseudoscorpions, need such a habitat, as these animals are very shy and need hides where they can retire quickly and most species need humid environment unless they would desiccate rapidly[2]. It has been observed that some species use cavities in combs or brood cells left empty lay eggs or to rest during their metamorphosis period[11]. For those who want to try out the experience, Piet van Dugteren offers to send pseudoscorpions in plastic containers in which they can survive for a couple of weeks. He nevertheless thinks that each beekeeper is able to maintain by him/herself a pseudoscorpions population.

The Case of Migrating Hives

The maintaining of compost heaps at the bottom of beehive might be difficult to apply in the case of migrating beehives, especially if these constantly remain on trucks.

Further advices

The use of acaricides is definitively prohibited with this method, since they are likely to be as (or even more) harmful to the varroa predators as to the parasite itself. Even "natural" substances such as thymol have been demonstrated to have a lethal effect on a number of pedofauna species due to their highly irritating properties.[12]

Bottom screens might also be contra-productive in this case since they would also represent a deadly fall for varroa predators especially if they are equipped with a greasy or sticky board.

References

  1. Wikipedia : Pseudoskorpione. http://de.wikipedia.org/wiki/Pseudoskorpion
  2. 2.0 2.1 2.2 2.3 2.4 Weygoldt P. : The Biology of Pseudoscorpions. Harvard University Press, Cambridge, Massachusetts, 1969. SBN: 674-07425-4
  3. Bérubé C. : Himalayan ceranaid:development assistance to preserve and promote Apis cerana beekeeping in Nepal. http://www3.telus.net/conrad/nepalbee.htm
  4. 4.0 4.1 4.2 van Dugteren P. : Scorpion Beneficial Organisms: Bestrijd de varroamijt op naturulijke wijze. http://www.scorpion-beneficial-organisms.com/
  5. Schöler A.: Untersuchungen zur Biologie und Ökologie der Herbstmilbe Neotrombicula autumnalis (Acari: Trombiculidae) im Hinblick auf Bekämpfungsmöglichkeiten sowie zu ihrer Bedeutung als Vektor der Borreliose. Mathematisch-Naturwissenschaftliche Fakultät der Rheinischen Friedrich-Wilhelms-Universität Bonn. http://deposit.ddb.de/cgi-bin/dokserv?idn=968399304&dok_var=d1&dok_ext=pdf&filename=968399304.pdf
  6. Wikipedia : Fluweelmijt. http://nl.wikipedia.org/wiki/Trombidium_holosericeum
  7. Kreuter M.-L.: Pflanzenschutz im Biogarten. BLV Verlagsgesellschaft, 4. überarbeitete Auflage, München 2001. ISBN: 3-405-15980-6
  8. van Dugteren P.: Personal correspondence with Piet van Dugteren, biologist and hobby beekeeper, January 2009
  9. Donovan, B. J., 2000: Could pseudoscorpions from South African beehives control our varroa? The New Zealand Beekeeper 7(6): 22-23. Quoted by « Heidecap », http://www.imkerforum.de/archive/index.php/t-8458.html
  10. 10.0 10.1 Garrit: Pseudoschorpioen. Contribution to the "Imker forum" http://www.bijenhouden.nl/forum/topic.asp?ARCHIVE=true&TOPIC_ID=4379
  11. Gonzales V. H., Mantilla B., Manhert V., 2008 : A New Host Record for Dasychernes Inquilinus (Arachnida, Pseudoscorpiones, Chernetidae), with an Overview of Pseudoscorpion-Bee Relationship. The Journal of Arachnology 35:470–474. http://www.americanarachnology.org/JoA_free/JoA_v35_n3/JoA-35-3-470.pdf
  12. Pesticide Action Network : Thymol – Identification, toxicity, use, water pollution potential, ecological toxicity and regulatory information. The PAN Pesticide Database. http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC35222#Ecotoxicity




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