Lime time – The Apiarist

Synopsis : Lime, linden, basswood … a fickle supply of very good honey and a possible bee killer. When and why does the lime yield smartly and what explains the affiliation of a few bushes with useless bees?

Advent

There’s an early 20^th Century pretend citadel close to me with intensive decorative gardens. Those gardens – or, extra correctly, the gardeners – are virtually indubitably accountable for the creation of Rhododendron ponticum to the realm. That is an invasive species and has unfold east with the existing wind, blighting the surroundings, choking the lifestyles out of the near-unique temperate rainforest and offering me with a nearly limitless provide of firewood.

Rhododendron supply no nectar or pollen for honey bees in the United Kingdom, however are well-known because the supply of mad honey in Nepal. The native bumble bees do consult with it, however I don’t take into accout seeing a honey bee at the flora.

Then again, on a extra sure notice those self same gardeners additionally planted a row of lime bushes alongside the street which at the moment are a stately 30-40 metres prime, in complete flower and which will every now and then supply a very good supply of summer time nectar.

Early on a relaxed July morning you’ll listen the bugs humming within the cover from no less than 75 metres away … now not simply honey bees, however bumbles, wasps, flies, moths, butterflies and all kinds of different issues as smartly. If we had hummingbirds right here (we don’t) they’d most definitely consult with the lime when it’s in flower.

The title ‘lime’ is derived from the Outdated English lind which at the start referred to the lime tree, however you’ll additionally regularly in finding in Center English poetry to imply any tree.

Lime bushes (Tilia sp.) also are regularly referred to as lindens (in continental Europe) and basswood (in the United States), however are unrelated to the citrus that produces lime fruit.

Lime species

There are 3 local or hybrid species of lime in the United Kingdom and a handful of alternative imported ‘exotics’, maximum of which I’m going to forget about (and which can be most effective most often present in decorative gardens):

• Wide-leaved lime (Tilia platyphyllos), is a local Eu tree however very scarce in the United Kingdom.
• Small-leaved lime (Tilia cordata), additionally local to the United Kingdom – however most definitely now not as a ways North as Scotland – and mainland Europe. There’s an attention-grabbing BBC podcast at the local small-leaved lime that’s price a pay attention.
• Commonplace lime (Tilia x europaea or Tilia x vulgare) which is a herbal hybrid of the broad- and small-leaved lime, going on naturally and in addition broadly planted in parks, gardens and regularly in city environments.

To confuse issues additional, some clones of commonplace lime are fertile and will subsequently additional hybridise with different limes. They are able to subsequently produce in an actual melange of relatively other paperwork making exact identity tough.

I’m beautiful sure the bushes close to me are commonplace limes. They’re large bushes; being a hybrid the bushes develop hastily and achieve a bigger general measurement than the opposite species. Additionally they have function dense shoots on the base and center of the tree, regularly making the trunk tough to tell apart.

No longer that the appropriate identity truly issues … all the above, and hybrids thereof, flower when the prerequisites are proper and supply nectar and pollen that our bees can use.

Flowering duration

I most often be expecting to peer the lime flowering in early to mid-July. Having a look again thru my number of footage, virtually all of the ones of flowering limes have been taken within the first 7-10 days of July. This most definitely manner they began flowering on the finish of June or very early in July, however I most effective belatedly realised they have been flowering later .

The books declare that the broad-leaved lime flora in June, with the others beginning in July. The one medical find out about I may just in finding in this used to be of lime in Lublin, Poland, the place the flowering (of all 3 species) seems to be 2-3 weeks previous than it’s in the United Kingdom.

Lime pollen is reasonably unique and its presence in environmental (air) samples over the years has been used to resolve the length and height of the lime flowering duration. The bulk is produced over a 3 week duration, with the date of height manufacturing various by way of up to a fortnight from 12 months to 12 months. As well as, there used to be really extensive variation between years at the overall quantity of pollen produced, with ‘deficient’ years generating ~25% or not up to within the ‘easiest’ years..

In closely treed spaces it’s obtrusive that it is just the sun-exposed portions of the lime that produce flora. The crown of the tree within the first {photograph} had plentiful flora and used to be alive with pollinators, however the decrease branches have been virtually devoid of the function cymes (the technical time period for the flora on person stalks) and the umbrella-like bracts which could have developed to forestall nectar and pollen being washed away by way of rain.

Flora and nectar

The typical lime produces essentially the most profuse flora, ~30,000, which is set 3 times the volume produced by way of the broad- or small-leaved lime (Jacquemart et al., 2018). Those figures have been according to cubic metre of tree. Understand that the hybrid commonplace lime regularly paperwork a considerably better tree, so a big one on the height of the flowering season will produce an enormous quantity of flora … explaining my skill to ‘listen’ the tree from down the hill on a relaxed morning.

I particularly say ‘morning’ as a result of nectar manufacturing tails off all the way through the day and is at its best possible within the morning.

Even supposing the average lime would possibly produce extra flora, it produces most effective part the volume of nectar according to flower than the small-leaved lime. On reasonable, every flower of commonplace lime produces 0.75 μl of nectar. One microlitre is one millionth of a litre, so a big tree bearing 30,000 flora according to cubic metre goes to be generating litres of nectar at anyone time.

The sheer quantity of flora, coupled with their accessibility and that of the nectar (no lengthy tongues wanted right here), greater than compensates for the reasonably low sugar content material of lime nectar (~35%).

Rain

In studying part a dozen medical papers on Tilia I didn’t see a unmarried connection with rainfall connected with feedback on nectar manufacturing and/or flowering of lime bushes.

Which is just a little unusual as a result of virtually each beekeeper who claims to grasp anything else about lime will say one thing like ’they want just a little of rain to yield smartly’ …

For instance, the day before today morning my pals at Kilbarchan and District BKA posted the Tweet above.

Which, making an allowance for the elements we’ve had just lately, made me assume … how a lot rain is wanted and when is it wanted for lime to yield smartly?

All the figures I’ve quoted above make no connection with the climatic prerequisites within the days and weeks previous the measurements being taken.

Used to be 2005 a specifically dry season in Lublin?

Did the rain arrive at simply the correct time in 2006 for the pollen depend (and subsequently the flora that produced the pollen and, possibly, the nectar that draws the pollinators to the flower) to be so prime?

If this is the case, when used to be ‘simply the correct time’?

I checked Hooper’s Information to Bees and Honey which slightly mentions lime. Hooper claims he’d observed no just right plants of lime honey for the reason that 1930’s. Manley’s Honey Farming most effective has a few sentences on lime. Each, without delay or not directly, counsel that lime isn’t a loyal nectar supply.

I don’t have an intensive library of beekeeping books, and feature reasonably few older books, so there could be one thing revealed I’m utterly ignorant of that explains the will for 100 mm of rain within the 3 weeks sooner than the onset of flowering.

Or is all the ’lime wishes rain’ factor a convoluted excuse dreamt up by way of beekeepers to provide an explanation for the loss of a just right summer time honey crop?

Rain this season

Past due Might and the primary 3 weeks of June this 12 months have been dry and scorching at the west coast. I do know the lime are flowering and that the bushes are hoachin with pollinators, together with my bees. Possibly the prerequisites had been preferrred?

Right here, for reference as a lot an anything, are graphs of the rainfall and imply and most temperature for the reason that 1^st of Might (or do I want to move additional again?).

Sadly it’s not likely to be a bonanza lime honey crop right here at the west coast. At the beginning I feel there are too few bushes and, being in a closely wooded house, most effective the cover truly flora smartly. Secondly it’s been 12°C maximum of as of late and raining exhausting 🙁 .

Lime honey

Lime honey is regarded as a top rate honey … no less than by way of me . It’s a transparent, runny honey, and is regularly a mild golden color. Darker lime honey virtually indubitably additionally comprises honeydew derived from the aphids which might be busy feasting at the lime bushes.

The honey regularly has a faint greenish tinge when freshly extracted and jarred.

You’ll learn all kinds of descriptions of the aroma of lime honey … I regarded up a couple of on-line they usually learn like a contribution to Non-public Eye’s Pseuds nook.

woody, pharmacy and contemporary

mint, balsamic, menthol and camphor

candy violets

mouth-watering citrus fruit flavour and tantalising notes of unpolluted mint

The only phrase I maximum go together with the flavor of lime honey is zesty. To my jaded palate it tastes deliciously contemporary and now not too candy.

In my enjoy it sells really well, with numerous repeat orders … ’may just I’ve any other part dozen jars of that closing batch?’

However, sadly, in settlement with Hooper and Manley, it does appear a ways from loyal. During the last 15 years I feel I’ve most effective had 3 or 4 seasons the place the lime has yielded smartly sufficient to generate important quantities of necessarily monofloral lime honey, regardless that I’m certain it options maximum years within the blended summer time blossom honey .

This modification should be environmental because the bushes are a fixture, by contrast to plants like OSR or box beans which range from 12 months to 12 months.

In fact, being environmental, there’s not anything a lot I will be able to do to switch the temperature, rainfall or humidity … but it surely would be just right to know what’s had to create a nice season for lime honey.

Lime bushes and bee deaths

Lime, specifically non-native species and the hybrid commonplace lime, are regularly planted in cities and towns. They’re reasonably proof against air pollution and – as opposed to the drip, drip, drip of honeydew – smartly fitted to an city setting.

There are a lot of stories of useless bees – each honey bees and bumble bees – beneath flowering lime bushes. Those return centuries (Koch and Stevenson, 2017 cite Bock, H Kreüter buch from 1551 which I will be able to neither supply or learn 😉 ) and comprises an editorial in Bee Global by way of Eva Crane (1977) that attributes those deaths to mannose sugars in lime nectar.

The species maximum regularly related to bee deaths is the silver lime (Tilia tomentosa), local to south-eastern Europe and south-western Asia, however which is grown as decorative tree in the United Kingdom.

The prior to now cited Koch and Stevenson (2017) imagine 5 possible reasons of those bee deaths:

1. Poisonous metabolites e.g. mannose or nicotine
2. Pesticides
3. Herbal reasons/outdated age
4. Hunger
5. Chemical deception

Regardless of Eve Crane’s statement that mannose is accountable, a number of unbiased medical analyses of Tilia nectar display it comprises no mannose. Since bee deaths date again to Medieval instances we will be able to most definitely rule out pesticides. The herbal reasons/outdated age is most likely refuted by way of the age of the corpses, maximum of which can be now not decrepit outdated bees.

The closing two possible reasons are in part connected.

Maximum bee deaths are related to the top of the T. tomentosa flowering duration and the advice is that the depleted nectar assets results in hunger. Foragers have depleted sugar reserves and can also be ‘rescued’ by way of being fed Tilia nectar. The chemical deception idea means that volatiles within the nectar (e.g. caffeine) reason chronic foraging even after nectar is depleted, once more resulting in eventual hunger.

Koch and Stevenson (2017) suggest that hunger reasons those extra bee deaths.

Tilia nectar research

A bit extra just lately Jacquemart et al., (2018) performed an in depth research of nectar from T. tomentosa and from the 3 UK species indexed above.

Not one of the nectars contained detectable ranges of mannose or nicotine. I feel this gorgeous a lot excludes those as the reason for the useless bees observed underneath lime bushes. Bumble bees – which at all times outnumber honey bees when the corpses are counted – fed both T. tomentosa or T. cordata (small-leaved lime) nectar confirmed equivalent ranges of survival to controls.

Scent the espresso …

While I feel we will be able to rule out toxicity and pesticides as the reason for the bee deaths, I’m now not completely satisfied that easy hunger is the reason.

There are different nectars to be had when the lime is flowering (and going over) – as an example, blackberry is having a look nice nowadays – so you would need to argue that the lack of a significant nectar supply (most definitely the most important unmarried nectar supply in an city setting) used to be related to a fidelity that averted the switching and exploitation of alternative nectars.

Fidelity is outlined as ‘proscribing visits to at least one flower sort, even if different rewards are available’.

That is the place the chemical deception idea originates.

Possibly there’s something in Tilia honey that successfully deceives bees to proceed to go back to the lime bushes after nectar stops being to be had?

One advice is that small quantities of caffeine in Tilia honey are accountable.

Espresso and bees merits a complete submit of its personal … there is proof that caffeine will increase foraging and recruitment, however those research are on honey bees. I’m now not certain equivalent research had been performed on bumble bees which account for 75% of the useless bees.

In the end, to confound the tale additional, honey and bumble bees vary of their herbal (decaffeinated) fidelity, with the previous appearing considerably larger constancy.

I feel our figuring out of the affiliation of Tilia foraging and bee deaths stays incomplete. Even supposing in large part involving the silver lime, different species had been implicated as smartly.

Within the interim, I’d identical to the elements to reinforce in order that my bees can profit from the row of enormous flowering limes simply down the street …

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Notes

Two ultimate ideas that got here to me simply sooner than posting … 

• lime would possibly not have developed to ‘intentionally’ (which isn’t how evolution works) mislead bees into increased fidelity and next hunger. The caffeine (or no matter) that deceives bees may well be a secondary made of the tree, unrelated to bees and pollination.
• are lime extra regularly related to bee deaths than different massive nectar assets? What number of useless bees had been counted in a box of oil seed rape? Lime are regularly planted in city environments the place, a) they’re simply accessed by way of bee-aware individuals of the general public, and b) the bottom underneath the tree is most often flat and both tarmac or carefully mown, quite than dense understorey and floor quilt in herbal forest.

References

Crane, E. (1977) At the medical entrance. Bee Global 58: 129–130 https://doi.org/10.1080/0005772X.1977.11097662. Accessed July 6, 2023.

Jacquemart, A.-L., Moquet, L., Ouvrard, P., Quetin-Leclercq, J., Hérent, M.-F., and Quinet, M. (2018) Tilia bushes: poisonous or treasured assets for pollinators? Apidologie 49: 538–550 https://doi.org/10.1007/s13592-018-0581-3. Accessed July 4, 2023.

Koch, H., and Stevenson, P.C. (2017) Do linden bushes kill bees? Reviewing the reasons of bee deaths on silver linden (Tilia tomentosa). Biology Letters 13: 20170484 https://royalsocietypublishing.org/doi/10.1098/rsbl.2017.0484. Accessed July 4, 2023.

Weryszko-Chmielewska, E., and Sadowska, D. (2010) The phenology of flowering and pollen free up in 4 species of linden (Tilia L.). Magazine of Apicultural Science 54: 99–108.