HomeBeekeepingOrganic management with Varroa - The Apiarist

Organic management with Varroa – The Apiarist

Synopsis : Honey bees had been eradicated on Santa Cruz Island following the introduction of Varroa. This gives some helpful classes for beekeepers on the significance of controlling Varroa.


Honey bees aren’t native to North America. They had been first launched in March 1622 at Jamestown, Virginia. The bees did effectively and unfold west, following the settlers. They lastly arrived on the west coast, in Santa Clara, California, 231 years later in 1853. Of a dozen hives ordered by Christopher Shelton, a Santa Clara botanist and rancher, just one survived the journey from New York by way of Panama.

Shelton barely had an opportunity to get pleasure from his bees as he was sadly killed when the steamboat Jenny Lind exploded in mid-April 1853.

Explosion on the steamboat Jenny Lind close to San Francisco, California

His bees survived and three hives derived from the unique inventory had been auctioned for $110 every. This was over 20 instances the worth of hives on the east coast at the moment and equal to over $4200 at present .

Californian Channel Islands map

Bees had been in demand they usually continued to unfold – each as feral swarms and as farmers established apiaries to assist pollination and for honey manufacturing. Having reached the California coast they had been then unfold to the close by islands. Bees had been transported to Santa Cruz, the most important of the eight Channel Islands close to Los Angeles, within the 1880’s. They flourished, however didn’t unfold to the opposite Channel Islands.

Subject station, nature reserves, pigs and bees

Santa Cruz Island is 250 sq. kilometres in space and lies ~35 km south of Santa Barbara. It is likely one of the 4 Northern Channel islands. There’s a lengthy central valley mendacity roughly east-west and the rocky mountainous land reaches 740 m. It has a marine temperate local weather; the typical high and low temperatures are 9°C and 21°C respectively and it receives about 0.5 m of rain a yr. It’s a good setting for bees.

From the 1880’s to 1960’s Santa Cruz Island was farmed – primarily for wine and wool, and from the 1940’s for cattle – however, after interval of college geology area journeys and the institution of a area station on the island, in 1973 it turned a part of the College of California’s Pure Reserve System (UC NRS).

Within the late 1970’s the Stanton household offered their ranching enterprise on the island to The Nature Conservancy who subsequently purchased further land on the jap finish of the island.

Santa Cruz Island is now collectively owned by The Nature Conservancy, Nationwide Parks Service, UC NRS and the Santa Cruz Island Basis and far of the island is used for scientific analysis and training.

However what concerning the bees?

Good query.

As a nature reserve and analysis station, the presence of non-native species causes a possible downside. Why go to all of the expense of managing a distant island analysis centre if all the identical species are current as on the mainland?

The Nature Conservancy due to this fact initiated a programme of eradicating non-native species. It took 14 months to eradicate the feral pigs, utilizing a mix of trapping, helicopter-based taking pictures and the discharge of sterilised radio-tagged pigs to find the stragglers .

However eliminating the bees took a bit longer …

Save the bees, or not

Why eliminate the bees? Absolutely they weren’t doing any hurt?

The introduction of any non-native species upsets the steadiness (if there’s ever steadiness) within the ecosystem. The launched species competes instantly or not directly with these native to the world and may result in native extinctions.

Jonathan Rosen has described how honey bee swarms, by way of occupying tree cavities beforehand used for nesting, in all probability performed a significant position within the extinction of the Carolina parakeet.

Pining for the fjords … a stuffed Carolina parakeet (nailed to its perch)

Competitors between honey bees and native pollinators has been effectively studied. It isn’t all the time detrimental, but it surely definitely will be. Moreover, it’s in all probability extra more likely to be detrimental in a small, remoted, island ecosystem. For instance, research confirmed that the presence of honey bees dramatically diminished visitation of native pollinator to manzanita blossoms on Santa Cruz Island.

As a part of the bigger programme of non-native plant and animal eradication on Santa Cruz Island plans had been drawn up within the late 1980’s to eradicate European honey bees. The anticipated advantages had been to:

  • eradicate competitors with native bee species (and presumably different non-bee pollinators, although these not often get a point out 🙁 )
  • scale back pollination of weed species (a few of which had been additionally non-native to Santa Cruz Island)
  • facilitate restoration of native plant species that had been reliant on native bee pollination
  • present a ‘area laboratory’ free from ‘unique’ honey bees during which comparative research of native pollinators can be potential

Killer bees

After the plans to eradicate Apis mellifera had been accepted a further potential profit turned obvious.

There have been rising issues concerning the unfold of Africanised honey bees which had lately reached Santa Barbara County. Though there was moderately compelling proof that swarms couldn’t cross from the mainland (e.g. not one of the different Northern Channel Islands had been colonised by bees) there have been issues that the Santa Ana winds would possibly assist blow drones from the mainland.

Had these drones arrived they could mate with the non-native however nonetheless native queens ensuing within the unfold of the dominant genes for defensiveness and absconding. The ensuing swarmy, aggressive Africanised bees would trigger issues for guests and scientists engaged on the island (as they’ve for guests to Joshua Tree Nationwide Park).

Aerial view of Santa Cruz Island

Though the introgression of African honey bee genes was used as additional justification for the eradication it’s not clear whether or not drones may really cross 30-40 km of open sea .

As an apart, there’s a present mission – the amusingly named ’Recreation of Drones’ – operating on the Isles of Scilly investigating whether or not drones can cross the ocean between St Agnes, Tresco, Bryher, St Mary’s and St Martin’s. These are, at most, 11 km aside (northern most tip of St Martin’s to most southerly level of St Agnes) however the person islands are solely separated by 1-2 km. I might be shocked if drones couldn’t cross that distance (at the very least with a robust following wind).

Killing bees

Adrian Wenner and colleagues set about exterminating the honey bees on Santa Cruz Island (Wenner et al., 2009). The method began in 1988 and led to 2007, and was divided into 4 phases:

  1. 1988-1993 – location and elimination of feral colonies
  2. 1994-1997 – organic management and colony demise
  3. 1998-2004 – monitoring residual honey bee exercise
  4. 2005-2007 – affirmation of the absence of honey bees

None of that is ’beekeeping’ – really it’s the precise reverse – so I don’t intend to dwell in a lot element on the work that was carried out. Nevertheless, the ’94-’97 part contains some sobering classes for beekeepers that are price discussing.

By the tip of part 1 the crew had recognized the existence (if not the situation) of at the very least 200 colonies and eradicated 153 of them.

Bear in mind, none of those had been managed colonies in hives. They had been all feral colonies occupying pure cavities in timber or rocks and so forth. Every colony was discovered utilizing painstaking bee lining methods much like these described in Thomas Seeley’s ebook Following the Wild Bees.

As soon as situated, nests had been destroyed with methyl chloroform and the cavity sealed to forestall it being reoccupied.

Some colonies couldn’t be accessed; in these instances acephate-laced sucrose-honey syrup baits had been used. This organophosphate has delayed toxicity for bees, permitting foragers to return to the colony which in the end dies. This method had been partially profitable in eliminating Africanised bees on the mainland (Williams et al., 1989), however baits wanted to be be monitored to keep away from killing the opposite bugs they attracted.

The scientists additionally deployed swarm traps (aka bait hives) and destroyed any swarms that moved in.

Collectively these interventions diminished honey bee numbers considerably – as monitored by common observations at pollen- or nectar-rich crops – however didn’t eradicate them.

Let there be mite

Heavy rains in January ’93 washed out roads on Santa Cruz Island, thereby severely limiting journey across the island. As well as, the earlier elimination of cattle had resulted within the near-uncontrolled development of fennel which now fashioned dense, impenetrable thickets.

Bee lining turned unimaginable and the scientists needed to invent extra devious methods to eradicate the residual feral colonies.

The method they selected concerned the introduction of Varroa.

Varroa was first detected within the USA in 1987 (in Florida) and have become widespread over the subsequent 5-8 years. Up till 1994 the honey bees on Santa Cruz Island had been freed from the ectoparasitic mite.

It was doubtless that they’d have remained that method … there was no beekeeping on Santa Cruz Island and the situation was too distant for bees to cross from the mainland (see above).

Varroa was already identified to have a devastating impression on the well being of honey bee colonies (Kraus and Web page, 1995). It was additionally identified that, apart from its native host Apis cerana (the Jap honey bee), Varroa didn’t parasitise different bee or wasp species (Kevan et al., 1991).

These two information – host specificity and harm inflicted – instructed that Varroa might be used for organic management (‘biocontrol’) on Santa Cruz Island.

Organic management

Organic management or biocontrol is a technique of controlling pests utilizing pure mechanisms resembling predation or parasitism.

The pest might be any dwelling factor – from animals to bacterial plant ailments – current the place it’s undesirable.

On Santa Cruz Island the pest was the honey bee.

In different research (lined in a earlier put up entitled Extra from the fungi ) biocontrol of Varroa has been investigated.

Management of the pest includes the introduction or software of a organic management agent. The important thing necessities of the latter have already been highlighted – specificity and harm.

Organic management works effectively when the specificity is excessive and the harm is due to this fact tightly focused. It may be an abject failure – or worse, it could actually harm the ecosystem – if the specificity is low and/or the harm is widespread.

The cane toad was launched to Australia to manage infestations of dollar cane beetle (a pest of sugar cane). Cane toads had been launched in 1935 and quickly unfold. Sadly, cane toads can’t leap very excessive and so singularly failed to manage the buck cane beetle which tends to keep excessive up the cane stems.

Feminine cane toad (not leaping)

But it surely will get worse; cane toads have a really catholic weight loss program and so outcompeted different amphibians. They launched overseas ailments to the native frogs and toads and – due to the poisons secreted from their pores and skin – harmed or killed predators that tried to eat them.


Vertebrates are normally poor organic management brokers as they are usually generalist feeders i.e. no specificity.

However Varroa is particular and so the harm it causes is targeted. The chance of ecosystem harm was thought-about low and so the mite was launched to the island.

Introduction of Varroa

In late 1993 Adrian Wenner caught 85 foraging bees and, to every one, added a single Varroa mite. The bees had been then launched and presumably flew again to their colonies … taking the hitchhiking mite with them.

Grownup mites – the darkish purple ones you see littering the Varroa tray after you deal with with Apivar – are mated females.

Resulting from their incestuous way of life a single mite is enough to provoke a brand new infestation.

The mated grownup feminine mite parasitises a honey bee pupa and produces a sequence of younger; the primary is male, the rest are feminine. You’re in all probability studying this earlier than the 9 pm watershed so I’ll go away it to your lurid creativeness to work out what occurs subsequent (or you may learn all of the sordid particulars in Know your enemy).

The presence of honey bees – decided by profitable swarm trapping or area remark at doubtless websites – was then often monitored over the subsequent 4 years.

Swarm numbers remained largely unchanged till 1996 after which dramatically decreased.

Numbers of latest swarms on Santa Cruz Island 1991 – 2005. Varroa introduction indicated.

It’s price noting that in ’94-’96 over 70 swarms had been present in pure websites or bait hives. There should have been a big variety of established colonies in 1993 to provide this variety of swarms.

However, from 1997 all of it stopped … solely a single swarm was subsequently discovered, in a pure cavity in 2002.

Monitoring and affirmation of eradication

From 1998 to 2004 the scientists continued to actively monitor the island for honey bees, specializing in 19 areas wealthy in pure forage. Though honey bees had been discovered – in reducing numbers – there have been too few to try bee lining to find their colonies.

On the websites being monitored, bees had been detected 9, 7, 4, 2 and 1 instances respectively within the 5 years from 2000 to 2004. After that, regardless of continued monitoring, no extra honey bees had been detected.

The ultimate part of the mission (’05-’07) confirmed the absence of honey bees on Santa Cruz Island.

While, as a scientist, I’m a agency believer that ’absence of proof doesn’t imply proof of absence’, as a beekeeper I’m effectively conscious that if there are not any scout bees, no swarms and no foragers (once I search in doubtless locations) then there are not any honey bee colonies.

Classes for beekeepers

I wouldn’t have recounted this sorry story – at the very least from a beekeeping perspective – until I believed there have been some helpful classes for beekeepers.

There are (at the very least) three.

The primary pertains to Varroa resistance, the second to Varroa transmission within the setting and the final to ‘secure’ ranges of Varroa. All require some ‘arm waving guesstimates’ , however have a great grounding in different scientific research.

Varroa resistance

There wasn’t any.

At a really conservative estimate there have been at the very least 20 colonies remaining on Santa Cruz Island in 1995. I say ‘conservative’ as a result of that assumes every colony generated two swarms that season (see graph above). In research of different pure colonies solely about 75% swarm yearly, which means the precise variety of colonies may have been over 50.

The numbers – 20 or 50 – matter as they’re each a lot increased than the variety of colonies most beekeepers handle (which, based mostly upon BBKA quoted statistics, is about 5).

Whether or not it was 20 or 50, they had been all eradicated following the introduction of 85 mites. Colonies didn’t develop into proof against Varroa.

This all took a number of years, however – inferring from the swarm numbers above – the overwhelming majority of colonies had been killed in simply two years, 1994 and 1995. This timing would match with quite a few different research of colony demise resulting from mites.

Wenner estimates that solely 3 colonies survived till 2001.

Leaving small numbers of colonies untreated with an expectation that resistance – and even tolerance (which is each extra doubtless and never essentially helpful) – will come up is a futile train.

I’ve mentioned this earlier than … it’s a numbers recreation, and a handful of colonies isn’t sufficient.

Varroa unfold

Wenner doesn’t elaborate on the place the foragers had been captured earlier than he added the mites. If I used to be going to try this I’d have chosen a number of websites across the island to make sure as many feral colonies as potential acquired mites … allow us to assume that’s what he did.

Nevertheless, with 85 mites piggybacking on returning employees, and someplace between (my guesstimated) 20 to 50 colonies, I believe it’s extremely doubtless that at the very least some colonies obtained none of this ’founding’ mite inhabitants.

But virtually all of the colonies died inside two years, and people who didn’t subsequently died with no additional intervention from the scientists. We don’t know what killed off the final surviving colonies however — and I do know I’m sticking my neck out right here – I guess it was the mites.

That is compelling proof for the unfold of Varroa all through the island setting, a course of that happens because of the actions of drifting and robbing.

If a neighbouring apiary to yours has mites some will find yourself in your hives … until you might be separated by a number of kilometres .

The transmission of mites within the setting is an excellent purpose to apply coordinated Varroa management.

One mite is all it takes

However, simply as I’ve argued that some colonies could have obtained none of the founding mites, I’m equally positive that others may have acquired very small numbers of mites, maybe only one.

And one mite is all it takes.

With out distinctive beekeeping abilities, resistance within the bee inhabitants or rational Varroa management there isn’t any secure stage of mites in a colony.

The extra you stop mites coming into the colony within the first place, and the extra of these which might be current you eradicate, the higher it’s to your bees.

Right here endeth the lesson 😉


It’s price noting that island populations do supply alternatives for the event of Varroa resistant (or tolerant) traits … if you happen to begin with sufficient colonies. Fries et al., (2006) describes the traits of the 13 surviving colonies on Gotland after leaving about 180 colonies untreated for a number of years. I’ve talked about this beforehand and can return to it once more to cowl some associated current research.


Fries, I., Imdorf, A. and Rosenkranz, P. (2006) ‘Survival of mite infested (Varroa destructor) honey bee (Apis mellifera) colonies in a Nordic local weather’, Apidologie, 37(5), pp. 564–570. Out there at: https://doi.org/10.1051/apido:2006031.

Kevan, P.G., Laverty, T.M. and Denmark, H.A. (1990) ‘Affiliation of Varroa Jacobsoni with Organisms apart from Honeybees and Implications for its Dispersal’, Bee World, 71(3), pp. 119–121. Out there at: https://doi.org/10.1080/0005772X.1990.11099048.

Kraus, B. and Web page, R.E. (1995) ‘Impact of Varroa jacobsoni (Mesostigmata: Varroidae) on feral Apis mellifera (Hymenoptera: Apidae) in California’, Environmental Entomology, 24(6), pp. 1473–1480. Out there at: https://doi.org/10.1093/ee/24.6.1473.

Wenner, A.M., Thorp, R.W., and Barthell, J.F. (2009) ‘Organic management and eradication of feral honey bee colonies on Santa Cruz Island, California: A abstract’, Proceedings of the seventh California Islands Symposium, pp. 327–335. Out there as a PDF.

Williams, J.L., Danka, R.G. and Rinderer, T.E. (1989) ‘Baiting system for selective abatement of undesirable honey bees’, Apidologie, 20(2), pp. 175–179. Out there at: https://doi.org/10.1051/apido:19890208.




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