nature's preservative

That Pitch Is No Curve Ball...
Where Do They Get Amber?

The story of amber obviously begins with pitch, or resin. And the story of resin focuses on trees which exude large quantities of the gooey stuff. In the temperate zone (defined), pines are some of the biggest producers (resin from pines is the source of turpentine).

But in the tropics the champion resin-producers are in the genus Hymenaea. These leguminous, flowering trees pump out astonishing quantities of the sticky stuff, probably as a defense against the many species of insects living in tropical forests.

termite in amber Termites have a better fossil record than most other insects. They are found in amber, as shown here, or in petrified wood, which may contain traces of their nests and galleries. Photograph by Laurie Minor-Penland.
Courtesy National Museum of Natural History, Smithsonian Institution.

"We have good evidence that, under many circumstances, resin produces defensive compounds," says Jean Langenheim, emeritus professor of biology at University of California at Santa Cruz, and a pioneer in the study of resin and amber. "In the case of bark beetles, there are excellent studies showing how resin defeats them. But the beetles are evolving. They can change."

Only a few pieces of ancient amber actually bear evidence of life. Baltic amber -- which ranges from 35 to 50 million years old, was long considered the cream of the crop because 1 piece in 500 contained insects or other remains.

Now, the emphasis on amber has shifted to the Dominican Republic (which shares the island of Hispaniola with Haiti). Dominican amber is slightly younger (from 25- to 40-million years old), but about one piece in 100 contains an interesting relic.

Once in a while -- probably too often for the insects concerned -- a little arthropod (defined) will get stuck in the natural flypaper called resin. (Insects that spend a lot of time around trees -- including borers and termites -- are most likely to suffer this slow death by en-goo-ment, but amber can also trap other fascinating remains -- like feathers, lizards, flowers and leaves.)

The Intricate Dance of Trees, Resin and Insects

leaf in amber

The leaf and flower of an ancient Hymenaea
tree, preserved in its own resin. Members of
the Hymenaea family still live in the tropics,
and produce large amounts of resin. Photograph
by Laurie Minor-Penland.

Courtesy National Museum of Natural History, Smithsonian Institution.

It's old news that resin seals wounds and gums up the works in boring and sucking insects. This is how it works: resin oozes from wounds, and the volatile (easily-evaporated) portion vaporizes into the air. The non-volatile portion that's left (which would eventually harden into amber) seals the wound and allows the tree to heal.

Scientists have long known that resin repels insects, but as experts the new field of chemical ecology (defined) have looked deeper into the subject, they've discovered a far more complex interaction.

Jean Langenheim, emeritus professor of chemical ecology at University of California at Santa Cruz, has studied resin and amber for most of her career ("I was kind of like an insect -- I got caught up in amber," she explains).

She notes that resin contains 30 to 40 compounds, some of which can:

Repels insects and in some cases attracts them.
Why would resin attract insects? Because insects and trees are locked in an evolutionary struggle, and the insects apparently evolved to understand the scent of resin as a signal saying "Breeding grounds here," or "Eat Me."

Attracts parasites of herbivorous insects that chew on the plant
(this serves the plant's and parasite's purposes at the expense of the herbivore); and

Contains chemicals that kills pathogenic fungi carried by bark beetles.
Often, fungi are the real villain (again, from the tree's point of view) and the main problem with bark beetles is that they carry fungi. (How does the tree "know" when to make this specialized resin? Apparently it's responding to some signal from the fungus to make this disease-fighting resin.)

How long have scientists been using biological matter trapped in amber?

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