pollen is food -- 7/06/17

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Today's encore selection -- from What Good are Bugs? by Gilbert Waldbauer. Pollen, the bane of allergy-sufferers, is actually a densely nutritious food:

"Although no one has counted how many of the world's almost 275,000 species of flowering plants are pollinated by insects, there is no doubt that insects pollinate the great majority. Of 44 species of crops commonly grown in North America, about 66 percent were identified by Samuel McGregor as being more or less dependent upon insects for pollination. Stephen Buchmann and Gary Nabhan wrote that, of the world's 94 major crop plants, 18 percent are pollinated by the wind, 80 percent by insects (92 percent of these by bees), and about 2 percent by birds.

Tulip anther with many grains of pollen

"David Roubik listed 1,330 species of plants that are cultivated or harvested from the wild in the tropics, but the pollinators of only 775 are known. About 88 percent of them are pollinated mainly by insects, 5 percent by bats, 1 percent by birds, and 6 percent by the wind. These figures agree with Kamaljit Bawa's earlier estimate that animals pollinate about 98 percent of all wild flowering plants in the lowland tropical rainforests of the world, and that the vast majority of these animals are insects. Bawa's estimate is particularly significant because tropical rainforests harbor so many different kinds of plants and animals. Edward O. Wilson wrote that tropical rainforests cover only 6 percent of the planet's land surface but are home to more than half the species of organisms on earth.

Pollen grains under electron microscope

"Most flowers reward their visitors with pollen or both pollen and nectar. Most produce large quantities of pollen, enough to fertilize many flowers and a generous excess to feed their pollinators. Pollen is a complete and nutritious food that contains carbohydrates, fats, proteins, vitamins, and minerals. Although nectar may contain small amounts of other nutrients, it is essentially a solution of sugar in water. Some insects thrive on a diet of only pollen, and a combination of pollen and nectar is the only food of all 25,000 known species of bees, but no insect can grow on a diet of only nectar. Some insects, such as hawk moths and many butterflies, eat only nectar as adults, but do not grow and must carryover from the caterpillar stage the proteins, fats, and other nutrients required to produce eggs. But many other adult insects retain few nutrients from the immature stage and must eat a complete diet including protein and other nutrients. Some eat pollen to supply these nutrients, among them the bees, certain flies, beetles, and butterflies."

author:	Gilbert Waldbauer
title:	What Good Are Bugs?: Insects in the Web of Life
publisher:	Harvard University Press
date:	Copyright 2003 by the President and Fellows of Harvard College
pages:	10-11