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Tag "Wildbienen"

Because pollen sucks.

It does! But if you prefer the smart word: it’s hygroscopic. It attracts water.

And where is water, there is rot.
Which is a problem when you are an insect that relies on pollen to feed its brood and therefore needs to store pollen for weeks, if not months. You may be more or less okay when in a desert or at least able to avoid the rainy season – but in our friendly fertile temperate zones, you’re not.

Still, they are here. Plenty of them. Mason bees and leafcutter bees and carder bees and many more.

ResearchBlogging.org

In their new paper, Christophe Praz and his colleagues suggest a scenario for just how this could have happened:

Before the bees began to feed pollen to their brood (i.e. before they actually became bees) they were something similar to today’s apoid wasps (Grabwespen). They were hunting other insects, paralysed their victims and dragged them into the broodnest where their prey would stay alive for several weeks before being consumed by the larvae.
You may find this disgusting or not, but keeping your food alive until consumption is definitely a good way to keep it fresh.
And there is nothing „primitive“ or old-fashioned about it. There are still plenty of wasps around who do exactly this. But this method does have its costs. Hunting takes time, it’s not without risks, chances to find prey are limited and so on. So when the flowering plants arrived and offered pollen as an alternative source of protein, the bees’ ancestors skipped their carnivorous habits and became all out vegetarians. Which – as we all know – turned out to be a smart move.

But before the flowers and the bees could become one of the biggest success stories on the planet, there was one more innovation needed.

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ResearchBlogging.org
While the honeybees were fine there was little interest in pollinators and pollination in general. People just took it for granted. But with the ongoing news about CCD and concerns about declining bee populations worldwide the interest in wild bees as natural pollinators and “backup” for honeybee pollination has risen sharply. It turned out, however, that very little was known about the changes in diversity and abundance of wild bees, despite their importance for natural and agricultural systems.

In North America, there had been fragmentary observations that populations of wild bees were declining, but the evidence for large scale range reductions has been lacking. Now a study has been published in PNAS that for the first time provides nationwide data for eight historically abundant species of bumble bees. And for some of them, the news is not good.

A team of researchers from the University of Illinois and Utah State University compared historical data of the past 100 years from museum collections with current data based on extensive surveys in the US between 2007 and 2009. They focused on eight target species – four expected to have relatively stable populations, and four where preliminary data suggested a decline. Overall, they had 73 759 specimens in the historical data set and collected 16 788 specimens at 382 sites for the current data set.

From this data, they were, for the first time, able to confirm the decline and to quantify its extent for four species: Bombus occidentalis, B. affinis, B. pensylvanicus, and B. terricola. All these species suffered a reduction in their geographic range as well as in their relative abundance. The species most massively affected is B. affinis, with an estimated reduction in range-area of 87% compared to historical data.

It is interesting to see that the declines in relative abundance appear only in the last 20 to 30 years, with, as the authors point out, “values from current surveys lower than in any decade of the last century”.

Concerning possible causes for the decline, they considered pathogens and genetic diversity in their study.
They consistently found higher infection levels of the microsporidium
Nosema bombi and lower genetic diversity in the declining populations, which makes these factors realistic predictors for the trajectory of a population. But they also state that cause and effect remain still uncertain. From the findings in the current study, it is not yet possible to determine, for example, whether the increased prevalence of N. bombi is the result of higher susceptibility to the pathogen or if N. bombi is simply more common in declining species for other reasons. Factors like habitat fragmentation, the loss of floral and nesting resources, or climate change were not considered in this study.

Cameron, S., Lozier, J., Strange, J., Koch, J., Cordes, N., Solter, L., & Griswold, T. (2011). Patterns of widespread decline in North American bumble bees Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1014743108

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Canada and the US have about 50 species of native bumblebees. For five of them, a rapid decline has been observed since the 1990s. Three species — Bombus affinis, B. terricola, and B. occidentalis — will now be submitted to the International Union for Conservation of Nature (IUCN) Red List of Threatened Species (cf NatureNews: Plight of the bumblebee) (via evolvimus).

Two main reasons for the decline are discussed. One is a fungal pathogen, Nosema bombi, that might have been introduced with commercially used bumblebees from Europe. The other might be climate change, which may cause a shift in flowering times and nectarflow that bumblebees are not adapted to.

Our special friend B. griseocollis still seems to do okay, though :)

Also this month, Anna Morkeski and Anne Averill of the University of Massachussetts published “Wild Bee Status and Evidence for Pathogen ‘Spillover’ with Honey Bees” in the American Bee Journal and in Bee Culture with a very good overview over the current research into bumblebee-decline.

(photo: A. Morkeski)

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While I am on the road scouting locations in Montana, my friends at home are becoming more and more bee-aware and sent me this picture. Some brood of some wild bees – but which one? Any ideas anybody?Während ich in den USA unterwegs bin und die Highways in Montana und Idaho abreise, erreicht mich dieses Foto von zuhause. Wildbienenbrut am Fenster – aber wer und was? Hat jemand eine Idee?

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Noch ein Nachtrag zum Maiwurm: Ölkäfer und einige andere Käfer scheiden an den Kniegelenken Tropfen gelber Hämolymphe aus, die das giftige Cantharidin enthalten. Es ist auch in kleinen Dosen für den Menschen giftig, schadet aber vielen insektenfressenden Tieren nicht. Es wurde im Altertum in Griechenland und im Mittelalter als Heilmittel bei Erkrankungen des Ausscheidungstraktes und zur Herstellung von Liebestränken verwendet. (Quelle: Jiri Zahradnik: Käfer Mittel- und Nordwesteuropas; Verlag Paul Parey, Hamburg und Berlin, 1985)

Laut Wikipedia soll die aphrodisierende Wirkung des Cantharidins schon den Truppen Napoleons beim Ägyptenfeldzug zum Verhängnis geworden sein, die in den Sümpfen des ägyptischen Nildeltas Frösche gefangen und verspeist haben sollen. Die Frösche ernährten sich angeblich vor allem von den besagten Käfern und konnten das Cantharidin einlagern, ohne selbst Schaden zu nehmen. Welche Froschart das gewesen sein könnte und was tatsächlich an dieser Geschichte dran ist, habe ich aber nicht herausgefunden.

One more note about this Meloe blister beetle: The curious yellow drop at the joint is hemolymph containing Cantharidin, a a poisonous chemical compound that has also been used as an aphrodisiac since antiquity. There are a lot of stories around this substance – from causing trouble for Napoleon’s troops in Egypt to horses that died from accidentally eating hay that contained blister beetles. I can’t confirm any of this, but I find this little black fellow increasingly interesting, bee parasite or not.

Foto: Florian Profitlich

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Okay, they might be parasites, these blister beetles (Meloe spec.), but you have to give them some credit for preseverence and ingenuity!

Bild: Einer von mehreren Maiwürmern, die ich im April in der Uckermark getroffen habe.

Der Maiwurm gehört zur Familie der Ölkäfer (Gattung Meloe) und genießt als Brutparasit an Wildbienen unter Bienenfreunden einen eher zweifelhaften Ruf.

Ökologen dagegen sind entzückt, wenn ich ihnen von meinem Fund berichte. Für sie ist ein gesundes, kräftiges Maiwurmweibchen wie dieses ein gutes Zeichen. Wo Maiwürmer sind, da ist die Welt noch in Ordnung. Sozusagen.

Denn der Maiwurm hat, wie viele Parasiten, einen ziemlich heiklen Lebenszyklus. Dazu gehört neben den normalen Problemen von Fressen und Gefressenwerden vor allem der Transport ins Nest des Wirtes. Also: Eiablage am Boden, dann schlüpft die erste Larve, ein Triungulinus (Dreiklauer). Diese Triungulinus-Larve muss jetzt vom Boden auf eine Blüte krabbeln (und das Tier ist zu diesem Zeitpunkt nur ein paar Millimeter groß! Bezogen auf die durchschnittliche Primel, die um diese Jahreszeit blüht, sagen wir 10cm hoch, ist das, als müssten wir ein 30stöckiges Hochhaus raufklettern!). Oben wartet die Larve, bis eine Solitärbiene vorbeikommt – keine Honigbiene, keine Hummel, und auch sonst nichts, es muss eine Solitärbiene sein und am besten ein Weibchen. Für die meisten der zwei- bis dreitausend Larven aus einem Gelege ist die Reise hier zuende. Sie sitzen auf ihrer Blüte und warten vergeblich bis sie verhungern, gefressen werden oder runterfallen (und es dann nicht noch einmal hoch schaffen…).

Die wenigen, die eine Wildbiene erwischen, haben genau eine Chance. Der Flug ihres Lebens. Sie krallen sich mit ihren Klauenfüßen im Pelz der Biene fest und lassen sich in deren Brutnest tragen. Dort lassen sie sich in den Brutzellen „einmauern“, eine Larve pro Zelle, bereit für die nächste Phase. Sie fressen das Bienenei und den Nahrungsvorrat, der eigentlich für die Bienenlarve gedacht war, und durchlaufen drei weitere Larvenstadien bevor sie sich verpuppen.

Und wenn das alles gutgegangen ist und im Frühjahr frische Maiwürmer im Garten auftauchen, dann heißt das für die Ökologen: hier sind zumindest mal so viele Wildbienen vorhanden, dass sie diese verrückten Käfer auch noch mit durchziehen können. So kann man es auch sehen.

Bild: Metamorphose des Ölkäfers Epicauta vittata: A – Triungulinus-Stadium, B – 2. Stadium, C – 3. Stadium, D – Scheinpuppe, E – Puppe, F – Imago. (Nordisk familjebok, 1904–1926)

Bis vor Kurzem war der Maiwurm eine häufige Frühlingsart, aber in den letzten Jahren hat die Zahl der Maiwürmer in Deutschland rapide abgenommen, vor allem wohl durch den Einsatz von Kunstdünger und Insektiziden, die die Wirtsarten vernichten. (Quelle: Jiri Zahradnik: Käfer Mittel- und Nordwesteuropas; Verlag Paul Parey, Hamburg und Berlin, 1985)

A very nice post on blister beetles in English can be found at The Marvelous in Nature. Also there: rare pictures of a Triungulin larvae (of a different beetle-species) hitching a ride on a bee!

Foto: Florian Profitlich

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