Mary Kim Baker, age 11, of Jenks, Oklahoma, for her question:

What is the pronuba moth?

Symbiosis means living together on the basis of friendly give and take. It is a term used most by biologists    but maybe we should adopt it for everyday human living. However, to gain possession, we would have to trade a few practices such as fighting and warfare, greed and selfishness. But the trade might be worthwhile. In any case, the pronuba moth is a perfect example of nature's harmonious system of symbiosis. There are several pronuba moths, also known as tegeticula moths. Each one has a beautiful story to tell, a very special story of symbiosis. Each little pronuba moth shares its life with a yucca flower, one of those handsome desert plants related to the lilies. It is a small, whitish moth with four oval wings that spread about one inch wide. Chances are you would never notice it fluttering through the desert air. However, you would certainly notice the tall, waxy white spires of blossoms that sprout up from the yucca plants. But without the little pronuba moth, this generation of handsome yuccas would be the last one.

As usual, nature begins this story with perfect timing. The yuccas open their towering blossoms right when the little pronuba moth is ready to lay its eggs. In order to produce pods of fertile seeds, the yucca flower must get pollen from its male stamens to fertilize its female pistil. Many flowers tempt bees and other insects with sweet nectar to do this for them. As a bee dips down for a sip of nectar, the dusty pollen rubs off on its fuzzy coat    and later brushes off by accident where the flowers need it.

But most insects do not visit yucca flowers; and besides, their pollen is too sticky to brush off. This is where the pronuba moth comes to the rescue. It prods a hole in the ovary of a yucca blossom and lays its eggs in it. Then the moth scrambles onto the stamens and uses special parts on its mouth to gather up gobs of the sticky pollen. It takes the pollen back to the ovary where the pronuba eggs are waiting. This completes its part of the bargain and off it flies. The pollen, of course, fertilizes the flower and its seeds start to develop. In time, the moth eggs hatch and the hungry little caterpillars dine on the ripening seeds. They may eat most of them, but almost always a few are left untouched. At last jt.~e greedy grubs are satisfied, and they turn into sleeping chrysalises. Meantime the yucca pods burst and shed their ripened seeds to become future yucca plants.

This give and take between the yucca and the pronuba moth is a perfect example of symbiosis. The yucca needs this special moth to help produce its seeds. The moth needs some of the tender ripening seeds to feed its caterpillars. The drab little moth and the big handsome yucca depend on each other to survive    and without the give and take of symbiosis, both of them would perish.

Yuccas are often transplanted to gardens far from their native deserts. They thrive and sprout their tall spires of showy blossoms. But their little moth partners are not around. So the lovely flowers fade away without leaving any fertile seeds. This symbiosis works only where the yucca and the pronuba live as neighbors.