Bottom Screens

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Bottom Screens

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How does it work?

Due the grooming behaviour of bees and the hustle and bustle in the hive, the varroa mites often loose grip and fall down, but are agile enough to climb back to parasite the bees again. With bottom screens, the mites fall through a screen and land on a greasy, sticky or dusty board, which prevents them to climb back, and die. The mesh or tubes are enough spaced to allow the mites to fall through, but not the bees.

There are two kinds of screens: a metallic mesh or - as a newer development - plastic tubes.

Efficiency

The mesh screen

Chapleau, a beekeeper and searcher from Quebec, has performed extended trials with mesh screens.[1] According to his researches, the mesh screen allows a varroa reduction efficiency of 70%, which can vary according to the different hives and environmental conditions.

The drawer has to be of a sufficient height to prevent the varroa from climbing back into the hive. Chapleau recommends a minimal height of 4 cm between the bottom and the mesh, and to clean up the board once a month to avoid a wax moth infestation. As a supplementary measure, the bottom board can be covered with a greasy or sticking substance that represents a supplementary hurdle for the mites. A beekeeper particularly recommended me to use chalk dust instead of grease, on which mites are completely unable to travel[2] (see also the Inert Dusts method).

The tube screen

This screen, invented by a beekeeper from Marseille, M. Legris, consists, in place of a metallic, of a row of smooth plastic tubes or ogive-shaped wooden slats spaced of 3.5 mm.[3]

Tubes are supposed to represent an improvement compared to a metallic mesh, as some mites have been observed to be agile enough to catch themselves on the mesh and walk on it. The plastic tubes are slippery, thus offer no grip to mites.

According to Le Pabic[4], many beekeepers reported apiaries completely free of varroa without complementary treatment using tube screens, while witnesses found in different beekeeper newsgroups are very mixed (some are "very satisfied", while some went back to mesh screens after having tried them) and trials in academic context could not confirm their efficiency, even if colonies in hives equipped with tube screens were found out to be stronger than colonies without them[5].

As for the mesh screens, there seem to be certain hive and environmental factors that affect the efficiency of the tube screens. More trials need to be performed on the longer term and in different exploitation conditions and on the field to determine in which conditions screens are most effective.

Risks

No obvious major risks for the bees have been reported.

Some beekeepers using tube screens have mentioned cases of robbing by bees that are alien to the colony taking advantage of the spaces between the tubes to enter the hive.[6]

Closed bottom or not?

Chapleau[1] recommends using a drawer with a closed bottom, which presents the two following advantages:

  1. A closed bottom prevents from cold pervading into the hive as this might compromise the health of the colony, the more low temperatures have been found out to be favourable to the development of varroa[1].
  2. A closed drawer allows counting the varroas that have fallen through the screen, which allows in turn an evaluation of the infestation and of the efficiency of the screen of the treatment if a complementary treatment is used.

In contrast, the developers of tube screens recommend leaving the bottom of the hive open, as, according to them, good ventilation results in higher mite fall.[4] According to some witnesses, the traditional basket hives that have no bottom at all are less vulnerable to varroa.[7]

If this seems contradictory to Chapleau's assertions, it has to be considered that the experimentations quoted of both types of screens here took places in very different climates: Chapleau experimented in Québec, where winters are long and cold, while the experimentation of the tube screens took place in the south of France, where the winters are rather mild. Beekeepers that have experimented tube screens in cold climates, like mountain areas, reported increased winter stocks consumption by bees, thus preferred to install a closed bottom, at least for the winter.[8]

Practicability

Bottom screens are available from beekeeping material suppliers and easily mounted on a hive.

Further advice

The method can be combined with varroa knockdown methods, like smoking or dusting. It is not compatible with the method using varroa predators methods, as these would equally fall though the screens due to their small size. A greasy/sticky/dusty bottom would also constitute a deadly trap to the cohabitants of bees, thus is not recommended in "hard-core" organic beekeeping.

Some bee lineages have been observed to have developed a more aggressive grooming behaviour against varroa.[9][10][11] The method takes advantage of this evolution and makes it rewarding for the bees.

The bottom screen is simple, economical and non-polluting control method that can be used during the honey flow period, as it represents no risk for the honey's quality.

References

  1. 1.0 1.1 1.2 Chapleau, J.-P., 2003: Experimentation of an Anti-Varroa Screened Bottom Board in the Context of Developing an Integrated Pest Management Strategy for Varroa Infested Honeybees in the Province of Quebec. accomplished within the framework of the "Appui au développement de l'agriculture et de l'agroalimentaire en région 2000-2003" programme of the "Ministère de l'Agriculture, des Pêcheries et de l'Alimentation du Québec, Canada" Regional district of l’Estrie), Final Report. http://www.countryrubes.com/images/AV-BOTTOM_BOARD.pdf; French version under: http://www.apinovar.com/articles/anti-varoa.pdf
  2. Batz W., 2009: personal conversation with Walter Batz, beekeeper, in 2009-09-29
  3. Leclercq B., 2008a : Le plateau grillagé. ApiWiki. http://www.mottoul.eu/apiwiki_ver3/index.php?title=Le_plateau_grillag%C3%A9
  4. 4.0 4.1 Le Pabic J.-P., 1997: Présentation du plateau à tubes HAPPYKEEPER. Apiservices. http://www.beekeeping.com/happykeeper/index_fr.htm
  5. Malraux J.-B., 2007: Essais sur le plateau de fond de ruche à tubes "Happykeeper". CFFPA de Vesoul. http://www.apiculture.com/happykeeper/rapport_1105.pdf
  6. Apiservices - Forum - General beekeeping, 2007: Plancher happykeeper. (Post not available online anymore)
  7. van Dugteren P. 2009: personal correspondence per email with Piet van Dugteren, biologist and beekeeper, on 2009-04-28
  8. FUNDP, Liste « Abeilles », 2005: Facultés Universitaires Notre-Dame de la Paix, Namur, Discussion « plateau à tubes suite d'Hivernage » (Post not available online anymore)
  9. Le Conte Y., 2004: Honey bees surviving Varroa destructor infestations in France. UMR INRA/UAPV Ecologie des Invertébrés, Laboratoire Biologie et Protection de l'abeille, Avignon, France. http://www.culturaapicola.com.ar/apuntes/sanidad/varroa/varroa_destructor_francia.pdf
  10. Leclercq B., 2006: Conduite naturelle contre Varroa. Fédération Royale des Unions Professionnelles Apicoles du Hainaut. http://www.abeille-hainaut.be/FRUPAH/index.php?option=com_content&view=article&id=42&catid=25
  11. van Dugteren P. 2009: personal correspondence per email with Piet van Dugteren, biologist and beekeeper, on 2009-05-09




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