Barth includes a little of the history of his subject and very occasionally waxes lyrical, but Insects and Flowers is genuine popular science, not the mix of history, biography, and travel narrative with a small smattering of science that passes as such these days. It even includes proper references into the scientific literature. On the other hand, though some details of experiments and experimental methodology are included, there's nothing that requires any specialist background. Barth's explanations are easy to read and are backed up with excellent diagrams and line-drawings and a good assortment of black and white and colour half-tones.
As a teaser, Barth begins with figs and fig wasps, one of the more spectacular examples of interdependence between insects and plants. He introduces flowers, their forms and purpose, the alternatives of self-pollination and cross-pollination, and the transport problem posed by the latter. And he surveys the different kinds of pollinating insects and describes the sociobiology of the bee hive. Four chapters on "collection" then cover pollen grains, the "baskets, brushes, and sweeping machines" used to collect them, nectar, and the "biomechanics of the lepidopteran proboscis" and nectar-collecting more generally.
"Nectar is basically sugar-water. Its total sugar content amounts to about 40 percent, though it can fluctuate widely among different species. The spectrum of possible concentrations is indicated by two extremes: 8 percent for the crown imperial (Fritillaria imperialis) and 76 percent for the marjoram (Origanum vulgare). [1,2] In addition to the sugars (sucrose, glucose, fructose) other substances are present in relatively small amounts. Among them are amino acids, proteins, organic acids, phosphates, vitamins, and enzymes."
That takes up about a third of Insects and Flowers; the larger part of it is devoted to insect behavior and sensory physiology. First Barth covers the insect visual system. Insects can see colours: they have trichromatic vision like humans, but most are red blind and ultra-violet sensitive. This is obviously central to understanding flower colours and the presence of visual "guideposts" for pollinators. Insect visual information processing and pattern recognition distinguish shapes based on figural intensity and figural quality.
"The wild radish (Raphanus raphanistrum), a bothersome weed to the farmer, in England grows in wild populations with a white and a yellow variety. The yellow form reflects ultraviolet in addition to yellow and hence is bee-purple to the insects. The white form reflects uniformly over the entire visible spectrum, and hence is one of the quite rare bee-white flowers. Do these differences have any adaptive value to the plant? Do the insect visitors prefer one of the two flower colors? Q.O.M. Kay, at the University College of Swansea, tested this possibility very thoroughly and directly in field experiments. ..."
Next Barth turns to insect smell. Simple experiments show that "the olfactory sense of the bee performs very like that of humans" — neither can compare with the sensitivity of dogs, eels, or male silkmoths. Bees have tens of thousands of pore plates on their antennae, which they can use for "3-D smelling". Flies, beetles, and butterflies use other kinds of "noses" as well as pore plates — and flies can taste with their feet.
"The ecological significance of this proboscis reaction is obvious. The sensory hairs on the feet apply a preliminary chemical test to things they encounter — puddles of water, the marmalade on the breakfast table, fatty substances in carrion and dung, and also potentially injurious substances — before the insect brain gives the command: stop and extend the proboscis. The animal does not actually begin to suck until the substance already classified as acceptable by the feet has passed a second test by sensory hairs at the end of the proboscis."Barth explains the elementary physiology of sense organs. He also covers perfume collection by orchid bees (the purpose of which is only partly understood) and plants that mimic female insects.
Other topics covered include the ability of insects to learn (and forget) and to keep track of time, the language of the bees and its evolution, and energy economy and temperature regulation in bumblebees. A final chapter looks at the evolutionary history of flowering plants and insects and the coupling between them.
The German original was published in 1982, but for this 1991 translation Barth added twenty pages of notes on work done since then. Insects and Flowers is not currently in print; copies may be available secondhand or from libraries.