Do elderberry flowers self pollinate to produce berries, or do they require an insect source?

Question

If so, is there a "specific" species of insect that more commonly pollinates them? (I'm in Central Missouri) My understanding, is that there has never been any known proven evidence (only theories) about this. I'll be anxious to read all your comments, or any documented literture you may have to share. Thank you!

Answer 1

(I'm assuming you're talking about Sambucus -- common names can often be different in different areas).

Here in the UK we get Sambucus nigra growing very commonly as a native, and this species also seems to be grown as a garden plant in the US and elsewhere.  Other species of Sambucus are grown too, and it seems to be well established (at least in S nigra and S canadensis) that more than one cultivar is needed to set seed.  However, some references say, for example "self-fruitful, but bigger crops with two cultivars".

This suggests that they are partially self-fertile -- but it's quite possible (as with many other plants) that varieties and species vary in their self-fertility.

  

Flowers of this type are not usually pollinated by particular species of insects.  The broad umbel of flowers forms an easily accessible platform rich in food, and is visited by a very wide range of insects, including beetles, flies, hoverflies, bees, butterflies, moths and so on.

Flowers pollinated by particular species tend to be larger, often with some kind of mechanism making it hard for other species to find them or gain access (perhaps a hinged "door", a spring-loaded part to kick off smaller insects, an extra long nectar tube, a shape to fit the insect, or even a trap baited with a food or sexual scent).

Producing pollen and nectar is an expensive process for plants.  There is a pay-off between attracting lots of non-specialist insects as pollinators (which risks them wasting the pollen by carrying it off to the wrong species altogether), and restricting access to a particular co-evolved type of pollinator (which makes it likely they'll take it to the right flower, but risks too few pollinators turning up at all).  Some plants go one way, some the other -- and of course others routinely self-pollinate or use the wind.  Some, like many dandelions (Taraxicum), hawkweeds (Hieracium) and brambles (Rubus) have seeds which grow as clones of the mother plant (apomixis) and are not the result of true fertlisation at all.

Umbel-type flowers are often also visited by predators hunting the nectar and pollen feeders -- for example, crab spiders (Thomisidae), soldier beetles (Cantharidae) and wasps and hornets of many kinds.

In the UK elder is rarely grown in gardens, as it's so common in the wild (I can even see a good big bush from where I'm sitting)  When it is grown, it's generally as varieties with unusual leaf colour (variegated, golden or purple), or unusual leaf shape.  Not much point in growing it for flowers or fruit here, as the hedges are full of it and one can always find far more than one could ever use!  We do sometimes make elderflower or elderberry wine, or elderflower "champagne" (non-alcoholic, much like lemonade) -- also elderberry jam or jelly.  The flowers are supposed to be nice deep-fried in batter, though I've not tried that.

Regards, Richard