MOST OF OUR GARDEN PLANTS have flowers at some time during their growing cycle. Many, of course, are ornamentals planted primarily for the flowers they produce. Many useful insects find the flowers just as attractive as we do, but for different reasons.
Flowers originally developed as showy changes to attract the attention of insects for pollination. Later modifications adapted some flowers for pollination by birds, and even bats. Many flowers returned to dependence upon the original agent of pollen dispersal, the wind. These have usually lost the eye-catching colors, forms, and odors that characterize flowers as most of us know them. Although some of these (like the grasses) are important in the garden, we grow them for other features than flowers.
Fundamental to all flowers are the floral structures required for reproduction. The female elements (stigma, style, and ovary) and the male elements (pollen, anther, and stamens) may be on the same or different plants. If on the same plant, they may be in the same or different flowers. In general, the farther apart the sexual parts are, the more dependent the plants become upon an agent of pollination to distribute the male pollen to the female pistil.
Hummingbirds and other birds provide this service for a few plants, bats also are known to pollinate some plants, but the most abundant and important pollinators are the insects that visit the flowers for food.
The pollen usually available in flowering plants provides the protein food required by many insects, particularly the bees. It is often produced in great quantity. Many kinds of bees depend upon it for supplying their young with protein, lipids, vitamins, and minerals.
Supplemented with nectar (often converted to honey), pollen thus becomes a necessity for bees, and they have evolved many remarkable structural adaptations to help them collect and handle pollen. Plants too have changed in complicated ways to take advantage of the visits of bees and other insects.
One of the most interesting of the many complicated relationships between plant and insect is that which has developed between the yucca plant of the Southwest and the yucca moth. The showy white flowers are visited by the yucca moth which purposefully scrapes pollen from the stamens and stuffs it into the funnel-shaped stigma after inserting eggs in the ovary below. This procedure guarantees food for the moth offspring which feeds on the developing ovules. The plant loses a few seeds, but is guaranteed pollination.
Other groups of insects show strong attractions to certain types of flowers. These may be roughly grouped in the following way:
Insects attracted to pollen flowers. Syrphid flies, colorful soldier flies, pollen-feeding beetles, and many pollen-collecting bees are often seen on poppy, rose, potato, elderberry, and similar flowers that provide pollen but no nectar. Male bees, moths, butterflies, or hummingbirds, interested only in nectar collection, are not usually attracted to these.
Insects attracted to flowers with exposed nectar. Short-tongued bees, flies, and many kinds of wasps are frequent visitors to the flowers of carrot, maple, saxifrage, euphorbia, poison-oak, and grapes. The flowers are usually inconspicuous, but it is easy for these insects to obtain the nectar.
Insects attracted to flowers with partly concealed nectar. Syrphid flies, short- and long-tongued bees, honey bees, and a few butterflies are attracted to the moderately showy flowers of stone fruits, strawberry, raspberry, cactus, buttercups, and cruciferous plants.
Insects attracted to flowers with concealed nectar. Many sorts of bees, wasps, and butterflies are attracted to the generally conspicuous flowers of currant, blueberry, onion, melon, and citrus. Although the nectar is hidden there is often a copious amount.
Insects attracted to social flowers. A large variety of both nectar and pollen collecting insects, including long- and short-tongued bees, showy butterflies, flies, and colorful beetles are frequent visitors to the conspicuous composites such as dandelion, sunflower, and aster. The showy “petals” are actually sterile flowers used to attract insects to the many tiny fertile florets of the central disk. The nectar in these “flowers” is usually hidden in narrow corolla tubes and the insects usually have to force their tongue past the stigma and stamens to reach the nectar.
Flowers adapted for bees. Only medium- to long-tongued bees can operate the sometimes complex mechanisms protecting the pollen and nectar of legumes, mints, sages, violets, delphinium, iris, etc. These flowers are sometimes visited by butterflies and moths for nectar, but the insects generally do not operate the pollinating mechanism. Some flowers have nectar so deep that only bumblebees can reach it. Others have tough mechanisms requiring large powerful bees for pollination. Sometimes bees will bite holes in the flower tubes to “steal” nectar without pollinating.
Flowers adapted for butterflies and moths. Large, conspicuous, strongly perfumed flowers with nectar at the base of long narrow corolla tubes or spurs are visited principally by butterflies and moths, although some are also utilized by long-tongued bees and flies. Hummingbirds and honey birds are important pollinators in tropical areas. Examples in this group include honeysuckle, trumpet flowers, tobacco, phlox, and many orchids.
Flowers visited mostly by moths are generally open or fragrant only at night and are white or pale colored. Butterflies, on the other hand, visit flowers which are generally open and fragrant during the daytime and are variously colored.
Insect pollinators, most of which are bees, are directly beneficial to the plants they visit and as a result many are also indirectly of great benefit to man. Visits of pollinating insects to flowers usually result in the production of seeds and fruits. These seeds and fruits are very important elements in our diet and in our agricultural economy.
A partial list of crops known to require or benefit from insect pollination includes almonds, apples, cherries, cranberries, cucumbers, canteloups and watermelon, and strawberries. Lima beans, buckwheat, celery seed, mustard, rape, and sunflower are other seeds consumed by us that result from pollination.
A large number of seeds used for propagation require insect pollination. Some of the more important ones are alfalfa, asparagus, cabbage, broccoli, cauliflower, carrot, clover, onion, radish, rutabaga, and turnip. It has been conservatively estimated that bee pollination is essential to the production of $1 billion worth of agricultural crops. No one has been able to put a price tag on the value of pollination to wildflower seed production or conservation-plant maintenance.
In your own garden, visits by honey bees and other bees to your fruit trees, holly trees, pyracantha shrubs, cucumber, muskmelon, watermelon, squash plants, blackberry, raspberry, and strawberry patches are to be greatly encouraged. They are making vital contributions to the decorative or edible fruits and berries in your garden. To prove this, put cheesecloth or other screening material around some of these plants or flower clusters so that bees cannot visit the flowers. No bees; no fruit!
Many people are disturbed at the presence of bees and wasps in their garden because of the rather common fear of being stung. It is true that bees and wasps have stings and do use them in defense of their nests. However, very rarely are their protective instincts aroused while they are visiting flowers. It is extremely unusual for anyone to be stung by a foraging bee or wasp unless the insect is sharply disturbed—accidentally or otherwise.
Bees or wasps around their nests are much more easily aroused to defend the nests. If you have such nests in your garden, they should either be avoided or eliminated.
One group of bees may prove annoying in another way. Leaf-cutter bees snip circular pieces of tissue from the leaves of roses and other ornamentals. They use these to fashion cells in which they store pollen and lay eggs and in which their offspring develop. Some varieties of roses are very attractive to leaf-cutter bees and are sometimes almost defoliated. However, most leaf-cutter bees are excellent pollinators and we ought to overlook the occasional damage they do to some of our plants.
Since the pollinating insects described here make such an important contribution to our food production and ecology, we should make some compromises in our attitudes towards them. Even if the ones in your garden are not helping you, they, their relatives or offspring may be making some important visits to plants in your neighbor’s garden. Since bees are known to forage up to three miles; their environment encompasses a large area. Careless or uninformed use of insecticides can thus have far-reaching effects.
Some of the honey bees visiting your flowers may come from the colony of a neighbor who keeps bees as a hobby, as a 4–H or merit badge project, or for honey for his table or to sell. His bees are at the same time spreading the benefits of their activity indiscriminately around the neighborhood within a Smile radius. Considered in this light, we should find it easy to put into proper perspective their occasional misplaced defensive activities.