A Plague of Beetles

Published by mary on April 7, 2009 08:49 pm under Marantaceae

This morning our worker called us out to see what he called la plaga – a plague – of beetles. It was early morning, the beetles were on the back side of the leaf, so I was shooting in the bright, long-shadowed tropical sun hence the poor quality of this and the next image.

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.