Checkers and Chafers

Which came first, the flower or the bee?

Despite the setup, that is not a trick question.  It has an answer, and as is often the case where insects are concerned, the answer is best expressed with a beetle.  Or, in this case, two beetles.

When I first started studying pollination, I assumed that I would just be studying bees.  For the most part, that’s how it worked out, but I also assumed that there would only be bees to study. That turned out to be wrong.

Sure, I knew about the odd moth-pollinated orchid or bat-pollinated cactus, and I knew that the adults of many insect species live on nectar, and so provide opportunities for incidental pollination.  Still, I thought that the only real pollen specialists – that is, species that can digest pollen, that have specific adaptations for carrying and living with pollen, that show up for pollen even if the flower doesn’t have any nectar – are bees.

Then I saw this thing.

 

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Trichiotinus
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Leafcutter bee with scopa

This is a flower chafer, most likely Trichiotinus assimilis.  It’s a beetle.  In fact, it’s a scarab beetle, which places it (at least in the popular imagination) among the beetliest beetles of them all.  It was snacking on the flowers in a municipal hedge in Lake City, Colorado, in early July.

It’s obviously a flower-snacking generalist (you can see the crescents it chewed out of the edge of the petals) but its principal interest was the pollen in the middle.  It ate the pollen.  It bathed in the pollen.  It’s wearing the pollen: the hairs on its body are carrying at least a meal’s worth, and they seem peculiarly useful for the task.  In fact, the hairs on its abdomen are so good at holding pollen that I was immediately reminded of the scopa, the specialized hairs on the abdomens of megachilid bees.

At any rate, it was interesting enough to follow around for a while, but I eventually filed it under “insect oddities” and mostly forgot about it.



A year or so later, I found this:

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Trichodes

This is an Ornate Checkered Beetle (Trichodes ornatus), also eating pollen, except this time on the east slope of the Central Cascades.  It doesn’t have quite the impressive coat of hairs that the flower chafer does, but it’s not far off.

The really interesting thing here is that checkered beetles are not closely related to scarab beetles.  They're in the same suborder (Polyphaga), but that's not saying much: 90% of all described beetles are polyphages, so any taxonomic bucket large enough to hold both species is big enough to hold about a third of all the insects ever named, including everything from fireflies to rhinocerous beetles.  Aside from being beetles (and so having the basic beetle toolkit: a pair of rigid, unflappable wings, vaguely plier-like mouthparts, and a lifecycle that includes complete metamorphosis) the members of Polyphaga have almost nothing in common.  The name itself is wonderfully uninformative: basically, it's the record of a frustrated naturalist, hands thrown in the air, saying "Bah! These things eat everything!"… except in Greek.

In fact, the separation between the families of Polyphaga is older than flowers.  According to the most comprehensive beetle phylogeny that I know of (Hunt et al., _Science_ vol. 318, 2007,) the major groups of Polyphaga diverged in the Triassic period, before the first appearance of flowering plants.  In fact, the sequence runs something like this:

  1. Beetle diversification (upper Triassic)
  2. Moths appear (lower Jurassic)
  3. Flowers appear (lower Cretaceous)
  4. Bees appear (middle Cretaceous)

… then something smacked the dinosaurs, little shrew-like things climbed into the trees and learned to catch bugs with their fingers, and here we are, wondering why it’s so dang hard to get a beetle to hold still for a photograph.

<Ahem> I digress.

So, after their start in the upper Triassic, the ancestors of checkered beetles and flower chafers had to keep themselves occupied for a very long time before the Cretaceous rolled around.  Apparently, they killed time eating plants, but not pollen: herbivory is widespread among the Polyphaga, but pollen digestion is not.  (Pollen is tough stuff, and requires either specialized enzymes or really specialized mouthparts in order to eat.)  That means that the checkered beetles and flower chafers probably didn't inherit the ability from a common ancestor.  They picked it up as they went along, long after their relatives started eating plants… quite possibly in the late Jurassic, or early Cretaceous.

That means that the plants of the world didn’t have to wait for the wasps to get their act together before they started coevolving with insects.  The fuzzy beetles (and moths and probably some flies) were already there.

And that let the flowers come first.

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