As I recounted in my post last summer, the plant family Apocynaceae contains species with a very wide diversity of pollination systems – see: The evolution of pollination systems in one of the largest plant families: a new study just published – download it for free. Confirmed pollinators include bees, birds, moths, butterflies, flies, beetles, and wasps of a dizzying diversity. So I was intrigued to receive an email earlier this week from my colleague Prof. Dr Ulrich “Ulli” Meve of the University of Bayreuth with the subject line “Wasp expert needed”. Ulli is an authority on Apocynaceae taxonomy, also has an interest in their pollination biology, and is a co-author of the study last year.
Attached to the email were a couple of images showing a wasp visiting flowers of Cynanchum obovatum, an endemic species of Apocynaceae from northern and eastern Madagascar. Ulli had taken the photographs during field work there in preparation for the Flora of Madagascar project. Here’s the global distribution of the species according to GBIF records:
I was excited because Madagascar has a very rich diversity of Apocynaceae (between 500 and 1000 species). However we have flower visitor observations for only a small fraction of them, fewer than 20 species, and good evidence that the visitors are pollinators for only a couple of those.
I didn’t immediately recognise the family to which the wasp belonged: it didn’t look like either Vespidae or Pompilidae, two groups that are known pollinators of Apocynaceae. So I uploaded the shots to the Hymenopterists Forum on Facebook and within minutes had received an answer: it was a species of Scoliidae, commonly referred to as scoliid wasps. The distinctive wing corrugation found in this family is clearly visible on this image:
Scoliids are parasitoids of beetles and are some of the world’s largest wasps, but it’s not a very diverse family, with only about 560 described species, and only a single species in the UK (on the Channel Islands). Compare that with the Pompilidae and Vespidae, both of which contain c. 5,000 species worldwide.
Ulli tells me that when he saw the scoliid on C. obovatum “the wasp knew what to do with the flowers”, something I’ve experienced with vespid and pompilid wasp pollinated species in Africa: these wasps are really familiar with the flowers, they know how to work them to get a reward as they are regular and committed visitors. We believe that this is likely to be the legitimate pollinator of the plant, in which case it’s one of the few records for Scoliidae pollinating Apocynaceae, and the first for Madagascar. Other examples are mainly in South America, India and South Africa, and usually as one of a broad set of other wasps and/or bees visiting generalist flowers.
It’s interesting that this species of Cynanchum is one of the few in which the corona which covers the gynostegium (the fused sexual parts) is closed over:
That means it requires quite a strong, large insect to get inside and access the nectar. So the prediction is that the pollen masses (pollinaria) will be found on the mouthparts of these wasps. Intriguingly, a very closely related species C. repandum has no such closed corona, begging the question of whether it might be pollinated by a different type of insect:
For now this record will go into the Pollinators of Apocynaceae database as pollinator unproven, but i would be great if someone working in Madagascar could confirm the status of this pollination system.
My grateful thanks to Ulli for sharing his pictures and allowing me to tell the story of what may be a whole new Madagascan pollination system for our favourite family. Apocynaceae is full of surprises!