A Neotropical Savanna

The weevils that swarmed on the sandpaper plant when it was in bloom have been identified. I received this email from Dr. Henry Stockwell, who kindly performed the identification during his recent stay at the Smithsonian Tropical Research Institute.

The weevils that you sent me are named Solaria curtula, of the subfamily Baridinae. As I mentioned to you on the phone, the larvae have their development in stems near the ground of poor nutritional value and must make an effort to find pollen after they emerge from a brief pupal stage. This is one of the very few weevils that is found on a fern, Dicranopteris. This fern is very common and forms a mat of vegetative growth on bare red-clay slopes. The individual single plant may cover several square meters. It is the first plant to reclaim bare hill-sides after a land-slide. Can’t think of a plant that might be poorer nutritionally.

Someone had suggested to me that the weevils might be laying their eggs in the pistils of the sandpaper plant so that the larvae could develop along with the fruit. Dr. Stockwell said on the phone that such behavior would be extremely unlikely because of the known life cycle of this species, which he then described in the email, above.

I should also add that although I saw the weevils mating during their pollen-eating swarm, I did not see them laying eggs, nor did I see them spending much time near the greenish pistil of the flower, which is where they would have had to lay their eggs.

Thank you, Dr. Stockwell.

I have been going over the notes I made for the sandpaper plant that I watched bloom in January and February. It seems to me that are some astounding synchronies between flower “behavior” and insect behavior, so I’ve decided to summarize what I found.

There were two massive blooms, separated by a three-week period, and the sequence of events was the same each time. Here’s the chronology. All events – both flower development and insect activity – occurred about 30 minutes earlier in the day for the second bloom than for the first, so ranges of time are given.

Before sunrise – Flowers are just barely open and the stamens are barely exposed.

At sunrise - A few bees arrive.

Thirty minutes to an hour past sunrise – Flowers are fully open and the bees are swarming. (You may need to wait for the movie to load.)

The bees are collecting pollen and no doubt distributing it as well. The petals are as wide open as possible to attract the bees to the flowers, and the stamens (pollen-bearing male parts) and the pistil (female part leading to the ovary) are fully exposed to bee activity.

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In celebration of the 200th birthdays of both Charles Darwin and Abraham Lincoln, the sandpaper plant burst forth in bloom again today, this time attracting a new beetle.

The image is not as well focused as I would like, but the beetle appeared and then disappeared, never to be seen again. So this is what I got.

The other beetles, the weevils that I saw last year and also two weeks ago, returned, as did the bees. This time all insects were in much greater number – probably a thousand bees at this one plant by 7:30 in the morning. I had a harder time estimating the beetles, but there were easily twice the number that there were two weeks ago.

I do not expect this plant to produce more profuse blooms this season. Now is the time to gather all my notes and try to make sense of what went on.

In a much more humble celebration today, I launched another blog, The Accidental Botanist, where I can ramble on about plant things that are unrelated to our neotropical savanna.

Sunrise (6:49 AM): After watching this plant, the sandpaper plant, Davilla kunthii, for an entire month, I was beginning to wonder whether it would ever bloom. But on the evening of January 29, I saw quite a bit of yellow peeking out of the buds and the next morning at sunrise (6:49 on January 30 here in Potrerillos) when I arrived at the plant, the buds were ready to burst into bloom. A few bees were already hovering around the plant.

As the morning progressed and the flowers opened, it became clear there were two kinds of bees interested in this plant – a large one (circled), and a small bee. (or is it?), below. (The image below, as noted by a correspondent – with an Asian name I can’t translate – is a type of hover fly. I have some other images of the small bee, but they’re not clear enough to post.)

8:00 AM: At least a couple dozen bees were buzzing around. By 8:30 there may have been 50 or more. It was clear that the large bee, at least, was collecting pollen. My only image of this so far is fuzzy, but it’s not hard to see the orange pollen sacs.

8:30 AM: the first few weevils. The weevils are the entire reason I was sitting in the shade comfortably, with my coffee and notebook, watching this sandpaper plant put on its spectacular bloom. I had seen and photographed a weevil swarm last year, and Robin Foster of The Field Museum of Chicago suggested I look at the swarm more closely this year. I’m going to be tracking this plant throughout its blooming period to watch for these weevils.

That they are weevils has been verified by Dr. Henry Stockman who is this January at the Smithsonian Tropical Research Institute here in Panama and kindly looked at my images from last year. He suggested that it is possible that these weevils are eating the pollen – which is a rich protein source. As I watched, I could not see whether they were eating, but they certainly did not seem to be collecting it the way the bees were.
By the time the weevils arrived, some of the petals had already dropped from the flowers. The flowers had gone from opening bud at just before 7 AM to fully open flower, to the commencement of petal-dropping at 8:30 AM. One and a half hours. Astonishing!

9:30 AM: The number of bees was down and the number of weevils was up.

10:30 AM: The petals were seriously dropping off. I could hear the petals landing on the sandpaper-like leaves. They sounded like raindrops. There were even fewer bees, but the weevils were still there.

11:15 AM: Nearly all the petals were gone but several weevils stuck around. When the petals fall off, the cup-like green sepals, which underlie the petals, are left behind with the stamens. The weevils seem unperturbed by the absence of petals and simply crawl around the sepals looking for their pollen meal.

1:30 PM: The sepals were closing in on the stamens. A few weevils were still around, hoping to avoid getting trapped in the sepal jaws, I assume.

4:00 PM: The sepals are completely closed around the stamens. I saw one forlorn weevil crawling around on the sepal surfaces. Some sepals qwew separated enough to show yellow – they’re the ones that were bursting with petals to open the next day.

What a day for a plant! I’m sure Darwin would have loved the show. Remember his study of the “sleeping” leaves of the little machete plant, Erythrina? I wonder what he would have made of the opening and closing jaws of these sepals.