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Synopsis : Lime, linden, basswood … a fickle supply of wonderful honey and a possible bee killer. When and why does the lime yield nicely and what explains the affiliation of some bushes with useless bees?
Introduction
There’s an early 20th Century fake fortress close to me with intensive decorative gardens. These gardens – or, extra precisely, the gardeners – are virtually definitely liable for the introduction of Rhododendron ponticum to the realm. That is an invasive species and has unfold east with the prevailing wind, blighting the setting, choking the life out of the near-unique temperate rainforest and offering me with an virtually limitless provide of firewood.
Rhododendron present no nectar or pollen for honey bees within the UK, however are well-known because the supply of mad honey in Nepal. The native bumble bees do go to it, however I don’t keep in mind seeing a honey bee on the flowers.
Nonetheless, on a extra constructive 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 excessive, in full flower and which might generally present a superb supply of summer season nectar.
Pay attention … you may hear it from right here
Early on a peaceful July morning you may hear the bugs buzzing within the cover from not less than 75 metres away … not simply honey bees, however bumbles, wasps, flies, moths, butterflies and all types of different issues as nicely. If we had hummingbirds right here (we don’t) they’d in all probability go to the lime when it’s in flower.
The identify ‘lime’ is derived from the Previous English lind which initially referred to the lime tree, however you’ll additionally typically discover in Center English poetry to imply any tree.
Lime bushes (Tilia sp.) are additionally typically known as lindens (in continental Europe) and basswood (within the US), however are unrelated to the citrus that produces lime fruit.
Lime species
There are three native or hybrid species of lime within the UK and a handful of different imported ‘exotics’, most of which I’m going to disregard (and that are solely often present in decorative gardens):
- Broad-leaved lime (Tilia platyphyllos), is a local European tree however very scarce within the UK.
- Small-leaved lime (Tilia cordata), additionally native to the UK – however in all probability not as far North as Scotland – and mainland Europe. There’s an fascinating BBC podcast on the native small-leaved lime that’s value a hear.
- Widespread lime (Tilia x europaea or Tilia x vulgare) which is a pure hybrid of the broad- and small-leaved lime, occurring naturally and likewise extensively planted in parks, gardens and sometimes in city environments.
To confuse issues additional, some clones of frequent lime are fertile and might due to this fact additional hybridise with different limes. They will due to this fact produce in an actual melange of barely completely different varieties making exact identification tough.
I’m fairly sure the bushes close to me are frequent limes. They’re massive bushes; being a hybrid the bushes develop quickly and attain a bigger total measurement than the opposite species. Additionally they have attribute dense shoots on the base and center of the tree, typically making the trunk troublesome to tell apart.
Shoots and leaves
Not that the exact identification actually issues … the entire above, and hybrids thereof, flower when the circumstances are proper and supply nectar and pollen that our bees can use.
Flowering interval
I often anticipate to see the lime flowering in early to mid-July. Trying again by my assortment of pictures, virtually all of these of flowering limes have been taken within the first 7-10 days of July. This in all probability means they began flowering on the finish of June or very early in July, however I solely belatedly realised they have been flowering later .
The books declare that the broad-leaved lime flowers in June, with the others beginning in July. The one scientific examine I might discover on this was of lime in Lublin, Poland, the place the flowering (of all three species) seems to be 2-3 weeks sooner than it’s within the UK.
Lime flowering occasions in Lublin, Poland
Lime pollen is sort of distinctive and its presence in environmental (air) samples over time has been used to find out the length and peak of the lime flowering interval. The bulk is produced over a 3 week interval, with the date of peak manufacturing various by as a lot as a fortnight from yr to yr. As well as, there was appreciable variation between years on the full quantity of pollen produced, with ‘poor’ years producing ~25% or lower than within the ‘greatest’ years..
Annual lime pollen ranges in Lublin, Poland
In closely treed areas it’s apparent that it is just the sun-exposed elements of the lime that produce flowers. The crown of the tree within the first {photograph} had considerable flowers and was alive with pollinators, however the decrease branches have been virtually devoid of the attribute cymes (the technical time period for the flowers on particular person stalks) and the umbrella-like bracts which can have developed to forestall nectar and pollen being washed away by rain.
Lime can yield nicely in July …
Flowers and nectar
The frequent lime produces probably the most profuse flowers, ~30,000, which is about 3 times the quantity produced by the broad- or small-leaved lime (Jacquemart et al., 2018). These figures have been per cubic metre of tree. Keep in mind that the hybrid frequent lime typically varieties a considerably bigger tree, so a big one on the peak of the flowering season will produce a large quantity of flowers … explaining my skill to ‘hear’ the tree from down the hill on a peaceful morning.
I particularly say ‘morning’ as a result of nectar manufacturing tails off throughout the day and is at its highest within the morning.
Though the frequent lime may produce extra flowers, it produces solely half the quantity of nectar per flower than the small-leaved lime. On common, every flower of frequent lime produces 0.75 μl of nectar. One microlitre is one millionth of a litre, so a big tree bearing 30,000 flowers per cubic metre goes to be producing litres of nectar at anybody time.
Nectar sugar content material on the genus degree – Tilia starred
The sheer quantity of flowers, coupled with their accessibility and that of the nectar (no lengthy tongues wanted right here), greater than compensates for the comparatively low sugar content material of lime nectar (~35%).
Rain
In studying half a dozen scientific papers on Tilia I didn’t see a single reference to rainfall linked with feedback on nectar manufacturing and/or flowering of lime bushes.
Which is a bit odd as a result of virtually each beekeeper who claims to know something about lime will say one thing like ’they want a little bit of rain to yield nicely’ …
For instance, yesterday morning my mates at Kilbarchan and District BKA posted the Tweet above.
Which, contemplating the climate we’ve had just lately, made me assume … how a lot rain is required and when is it wanted for lime to yield nicely?
The entire figures I’ve quoted above make no reference to the weather conditions within the days and weeks previous the measurements being taken.
Was 2005 a very dry season in Lublin?
Did the rain arrive at simply the precise time in 2006 for the pollen rely (and due to this fact the flowers that produced the pollen and, presumably, the nectar that pulls the pollinators to the flower) to be so excessive?
If that’s the case, when was ‘simply the precise time’?
I checked Hooper’s Information to Bees and Honey which barely mentions lime. Hooper claims he’d seen no good crops of lime honey because the 1930’s. Manley’s Honey Farming solely has a few sentences on lime. Each, straight or not directly, counsel that lime isn’t a reliable nectar supply.
I don’t have an intensive library of beekeeping books, and have comparatively few older books, so there might be one thing revealed I’m completely unaware of that explains the necessity for 100 mm of rain within the 3 weeks earlier than the onset of flowering.
Or is all the ’lime wants rain’ factor a convoluted excuse dreamt up by beekeepers to clarify the dearth of an excellent summer season honey crop?
Rain this season
Late Might and the primary three weeks of June this yr have been dry and sizzling on the west coast. I do know the lime are flowering and that the bushes are hoachin with pollinators, together with my bees. Maybe the circumstances have been ideally suited?
Right here, for reference as a lot an the rest, are graphs of the rainfall and imply and most temperature because the 1st of Might (or do I have to go additional again?).
Temperature and rainfall
Sadly it’s unlikely to be a bonanza lime honey crop right here on the west coast. Firstly I feel there are too few bushes and, being in a closely wooded space, solely the cover actually flowers nicely. Secondly it’s been 12°C most of at this time and raining exhausting 🙁 .
Lime honey
Lime honey is taken into account a premium honey … not less than by me . It’s a transparent, runny honey, and is commonly a light-weight golden color. Darker lime honey virtually definitely additionally comprises honeydew derived from the aphids which might be busy feasting on the lime bushes.
The honey typically has a faint greenish tinge when freshly extracted and jarred.
You’ll learn all types of descriptions of the aroma of lime honey … I seemed up just a few on-line they usually learn like a contribution to Non-public Eye’s Pseuds nook.
woody, pharmacy and recent
mint, balsamic, menthol and camphor
candy violets
mouth-watering citrus fruit flavour and tantalising notes of recent mint
The one phrase I most affiliate with the flavour of lime honey is zesty. To my jaded palate it tastes deliciously recent and never too candy.
In my expertise it sells very nicely, with a number of repeat orders … ’might I’ve one other half dozen jars of that final batch?’
Lime leaf
However, sadly, in settlement with Hooper and Manley, it does appear removed from reliable. Over the past 15 years I feel I’ve solely had three or 4 seasons the place the lime has yielded nicely sufficient to generate important quantities of primarily monofloral lime honey, although I’m positive it options most years within the combined summer season blossom honey .
This variation should be environmental because the bushes are a fixture, in distinction to crops like OSR or subject beans which differ from yr to yr.
In fact, being environmental, there’s nothing a lot I can do to vary the temperature, rainfall or humidity … but it surely would be good to grasp what is required to create a nice season for lime honey.
Lime bushes and bee deaths
Lime, notably non-native species and the hybrid frequent lime, are sometimes planted in cities and cities. They’re comparatively immune to air pollution and – aside from the drip, drip, drip of honeydew – nicely suited to an city setting.
There are quite a few experiences of useless bees – each honey bees and bumble bees – beneath flowering lime bushes. These return centuries (Koch and Stevenson, 2017 cite Bock, H Kreüter buch from 1551 which I can neither supply or learn 😉 ) and consists of an article in Bee World by Eva Crane (1977) that attributes these deaths to mannose sugars in lime nectar.
The species most frequently related to bee deaths is the silver lime (Tilia tomentosa), native to south-eastern Europe and south-western Asia, however which is grown as decorative tree within the UK.
The beforehand cited Koch and Stevenson (2017) contemplate 5 potential causes of those bee deaths:
- Poisonous metabolites e.g. mannose or nicotine
- Pesticides
- Pure causes/outdated age
- Hunger
- Chemical deception
Regardless of Eve Crane’s assertion that mannose is accountable, a number of impartial scientific analyses of Tilia nectar present it comprises no mannose. Since bee deaths date again to Medieval occasions we are able to in all probability rule out pesticides. The pure causes/outdated age is probably going refuted by the age of the corpses, most of that are not decrepit outdated bees.
The final two potential causes are partially linked.
Most bee deaths are related to the top of the T. tomentosa flowering interval and the suggestion is that the depleted nectar assets results in hunger. Foragers have depleted sugar reserves and may be ‘rescued’ by being fed Tilia nectar. The chemical deception idea means that volatiles within the nectar (e.g. caffeine) trigger persistent foraging even after nectar is depleted, once more resulting in eventual hunger.
Koch and Stevenson (2017) suggest that hunger causes these extra bee deaths.
Tilia nectar evaluation
A bit of extra just lately Jacquemart et al., (2018) carried out an in depth evaluation of nectar from T. tomentosa and from the three UK species listed above.
Not one of the nectars contained detectable ranges of mannose or nicotine. I feel this beautiful a lot excludes these as the reason for the useless bees seen 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 related ranges of survival to controls.
Odor the espresso …
While I feel we are able to rule out toxicity and pesticides as the reason for the bee deaths, I’m not fully satisfied that straightforward hunger is the trigger.
Bramble
There are different nectars obtainable when the lime is flowering (and going over) – for instance, blackberry is trying nice in the meanwhile – so you would need to argue that the lack of a significant nectar supply (in all probability the biggest single nectar supply in an city setting) was related to a fidelity that prevented the switching and exploitation of different nectars.
Fidelity is outlined as ‘proscribing visits to at least one flower kind, even when different rewards are accessible’.
That is the place the chemical deception idea originates.
Maybe there’s something in Tilia honey that successfully deceives bees to proceed to return to the lime bushes after nectar stops being obtainable?
One suggestion is that small quantities of caffeine in Tilia honey are accountable.
Fidelity? … you guess
Espresso and bees deserves a full put up of its personal … there is proof that caffeine will increase foraging and recruitment, however these research are on honey bees. I’m undecided related research have been carried out on bumble bees which account for 75% of the useless bees.
Lastly, to confound the story additional, honey and bumble bees differ of their pure (decaffeinated) fidelity, with the previous exhibiting considerably higher constancy.
I feel our understanding of the affiliation of Tilia foraging and bee deaths stays incomplete. Though largely involving the silver lime, different species have been implicated as nicely.
Within the meantime, I’d identical to the climate to enhance in order that my bees can make the most of the row of big flowering limes simply down the street …
Notes
Two last ideas that got here to me simply earlier than posting …
- lime could not have developed to ‘intentionally’ (which isn’t how evolution works) deceive bees into elevated fidelity and subsequent hunger. The caffeine (or no matter) that deceives bees is likely to be a secondary product of the tree, unrelated to bees and pollination.
- are lime extra typically related to bee deaths than different massive nectar sources? What number of useless bees have been counted in a subject of oil seed rape? Lime are sometimes planted in city environments the place, a) they’re simply accessed by bee-aware members of the general public, and b) the bottom underneath the tree is often flat and both tarmac or carefully mown, fairly than dense understorey and floor cowl in pure woodland.
References
Crane, E. (1977) On the scientific entrance. Bee World 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 worthwhile 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 causes 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 launch in 4 species of linden (Tilia L.). Journal of Apicultural Science 54: 99–108.
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