Here’s the culprit.

Ted MacRae of Beetles in the Bush says that it is a member of the chafer group (subfamily Melolonthinae) of the scarab beetle family, but he did not have a species name for it. He says the larvae are likely somewhere in the soil, eating the roots of (other) plants.

Update: Ted kindly pulled some strings among his beetle expert friends. Here’s his report:

According to my friend, Arthur V. Evans, an expert in the family Scarabaeidae, the beetle in your photos is Magnus bolax of the subfamily Rutelinae (closely related to the Melolonthinae). I could not find any particular information about this species other than collection listings and various checklists; thus, its occurrence as a defoliating pest of your Calathea lutea seems to be a one-off thing. A nice picture of a mating pair can be seen on page 6 in the September 2007 issue of SCARABS, a newsletter devoted to the study of scarab beetles.

Magnus bolax is one of 541 species of scarab beetles that have been recorded from Panamá (Ratcliffe 2002) it is a hugely diverse family.

P.S. Another interesting factoid I forgot to mention  – the Latin word from which the genus name is derived means “large”, while the meaning of the specific epithet is “lump” – this beetle’s name means, literally, “large lump”.  I find that immensely amusing!

Ted’s note that this beetle is not known as a defoliating pest is supported by Carla Black, who has lived and observed in Panama for some years. Here’s what she had to say about la plaga:

This is the first year I am seeing damage on foliage from these beetles. A decade ago we had El Niño to blame for every strange event, and now we have Global Warming.

I am seeing a number of different species, judging by size and markings. They are all in the family of June beetle, Japanese beetle, or May beetle, but I haven’t made an effort to ID them. Sometimes you see a gorgeous shiny gold or silver one, making clear the attraction scarabs held for ancient Egyptians.

They are the adult form of white grubs (gongorongoros in the local parlance over here). When you have a grub in hand you can ID it to species with help on the internet – just look up white grub. Both the grub and the adult are common and destructive pests. The grub annoys lawn keepers mostly, though surely eats most everything underground.

  

The pics could be better, but you get the idea.

We have used a trap, and should again now. It was a light bulb about 12 inches from the ground outside, with a tray of plain water underneath. The beetles fall in and swim until they die; it doesn’t occur to them to crawl out or fly away. The beetles have a schedule, so we could turn off the light before going to bed. On the first night or two the toads clean out the tray, but then they can’t keep up and you have to do it yourself.

 

Thanks to both Ted and Carla for their interest, information, and observations.

The plant of the current infestation is a bijao, Calathea lutea. which can be used to wrap Panamanian foods such as tamales and bollos. I’ve started using the leaves to cover the stove-top chicken I make and it seems to improve the flavor as well as the moisture content.

Seeing the plant in this condition made me think back on its earlier days. Here it is in its pot in April 2007, a gift from my Spanish teacher.

In the ground in May 2008.

In the rainy season (November 2008).

It looks pretty healthy. I think it will survive this plague.

Luckily, the family that is helping me with my Spanish gave me a grand tour of their property last week, and they presented me with many plant cuttings and fruits and other wonders from their place. This plant was among the gifts.

One of the first things I noticed after potting it up was that the leaves folded up:

Being new to botany and gardening, I thought, well, it must be transplant shock. The next morning, the leaves were open again, and I breathed a sigh of relief. Okay, it’s not going to die on me. But then by noon, the leaves had folded up again.

It was time to figure out what is going on.

It did not take long to find the scientific name of the plant because the woman who gave it to me also was kind enough to write down its name in Spanish – bija, or bijao (for the leaf). I found the word bijagua in the index of my copy of Tropical Plants of Costa Rica, and there, on page 98, was my plant.

Its scientific name is Calathea lutea. Calathea means basket, referring to the form of inflorescence, and lutea means yellow. Since its name is descriptive of the flower, we should look at that:

The reddish parts are bracts, and they form the shape of the flower cluster, or inflorescence. An individual flower has been pulled out of one of the bracts and sits between the two stems on the right. The flowers appear only after the plants are mature and much taller than the one in my pot.

Calathea lutea belongs to the family Marantaceae, which is named for Bartolommeo Maranti, a 16th century Venetian botanist. Since the family is named after a person, we don’t get a description of the plant from the name, but it didn’t take long at Wikipedia to discover that Marantaceae is sometimes called the “prayer-plant family” because of the way the plants fold their leaves.

There’s a great description of this leaf behavior at the page on Form and Photosynthesis by Thomas J. Herbert, who has studied leaf movement in Calathea lutea in detail. According to Herbert, the leaf surface becomes vertical at night (this is called nyctinasty, in botanical language) and then more horizontal in the morning. By noon they’ve moved into a vertical position again – and they’ve folded their leaves. This time the movement is called paraheliotropism. Nyctinasty is activated by the red-sensitive pigment that causes a plant to flower in the spring because the days are growing longer or in the fall because the days are growing shorter. Heliotropism is activated by a blue-sensitive pigment.

But back to my original interest in this plant – as food wrapper. You can see from the first image that the leaves are large and attractive. They also have a waxy surface underneath, which can be seen when the leaves are folded. It’s always fun to guess why the first person decided to try using a plant in a new way. For one thing, there are plenty of these plants around – it is a pioneer species in the tropics, so it’s abundant in open areas. For another, to me, the leaves just look clean, and they’re plenty large enough to wrap food in…so….

I don’t yet know how to make tamales, but I do now know how to make Panamanian tortillas folded in one of these leaves. You simply place the waxy side of the leaf down on a skillet, place the tortillas on the leaf, and fold the top half of the leaf over the tortillas. Place a lid on top to hold the leaf in place and cook over a very low flame for 40 minutes. Turn and cook for an additional 30 minutes. They’re done.

You’ll notice that I haven’t given the recipe for the tortillas themselves – that’s a family secret!