Beneficial Insects for Gardens

Benefic and Value of Insects

Insects need to be studied carefully to distinguish the beneficial from the harmful. People have often gone to great trouble and expense to destroy quantities of insects, only to learn later that the insect destroyed was not only harmless but was actually engaged in saving their crops by eating destructive insects. Most entomologists have had correspondents send in the larvae of lady beetles with the complaint that they were injuring plants; at the same time overlooking the smaller aphids which were causing the injury and which these larvae were continually devouring.

Insects are beneficial to the gardener in several ways:

Insects aid in the production of fruits, seeds, vegetables,and flowers, by pollinizing the blossoms. Most common fruits are pollinized by insects. Melons, squash, and many other vegetables require insects to carry their pollen before fruits set. Many ornamental plants, both in the greenhouse and out of doors, are pollinated by insects for example, chrysanthemums, iris, orchids, and yucca.
Parasitic insects destroy other injurious insects by living on or in their bodies and their eggs. Insects also act as predators, capturing and devouring other insects.
Insects destroy various weeds in the same ways that they injure crop plants.
Insects improve the physical condition of the soil and promote its fertility by burrowing throughout the surface layer. Also, the dead bodies and droppings of the insects serve as fertilizer.
Insects perform a valuable service as scavengers by devouring the bodies of dead animals and plants and by burying carcasses and dung.

Many of the benefits from insects enumerated above, although genuine,are insignificant compared with the good that insects do fighting among themselves. There is no doubt that the greatest single factor in keeping plant-feeding insects from overwhelming the rest of the world is that they are fed upon by other insects. It is easy to see how the industry of insects and their devotion to purpose, when coupled with almost unlimited numbers, can benefit us when they seek and devour myriads of pests scattered over a farm or a forest.

Attracting Beneficial Insects

Attracting and maintaining a population of beneficial insects are important to managing insect pests in your garden with a minimum of pesticide sprays. Tiny parasitoid wasps are aggressive beyond their size when it comes to pursuing aphids and caterpillars. Lacewing larvae and ladybug larvae and adults make inroads on aphid populations. Ground beetles prey on a variety of ground-dwelling pests.

These various beneficial insects consume large numbers of pest insects, but their diets are not limited to other insects. In fact, many of the beneficial species have periods in their life cycles when they survive only on nectar and pollen. Therefore, planting a variety of insectary plants will ensure an adequate supply of nutrients to keep beneficial insects going strong. Insectary plants also include those plants that provide shelter for beneficial insects, another critical requirement.

At one time, hedge rows that separated one field or garden from the next provided an ample supply of insectary plants to feed and shelter a variety of beneficial insects. The wide variety of plants in a hedge row, including small trees and shrubs as well as perennial and annual weeds, typically leaf out and bloom earlier than most crop plants, providing beneficial insects with an early food supply.

Most gardens today are too small for a hedge row. An alternative is to plant a border of dwarf fruit and flowering trees mixed with flowering shrubs and perennials. Such a border could be a landscape feature and screen the vegetable garden from view. At the same time, it would provide many of the benefits of the traditional hedge row.

Plan an insectary border for successive bloom from early spring through fall, providing nectar throughout the season. This will not only satisfy the needs of many beneficial insects, but also provide color in the garden. Avoid vigorous chemical control of pests found in the insectary border; after all, you don't want to kill beneficial insects. Also, any pests in the border may become hosts for beneficial insects should prey levels be low in the garden you are trying to protect.

Including plants of different heights can be very important. Ground beetles require the cover provided by low-growing plants. Lacewings lay their eggs in shady, protected areas, so providing such places near crop plants is a good idea.

Selective weeding can encourage beneficial insects by leaving potential food sources in the garden. Allowing certain volunteers to remain in the garden is somewhat like random companion planting. Just know what weeds or volunteers are helpful. Not all blooms are equal -- large, nectar-filled blooms actually can drown tiny parasitoid wasps. Tiny flowers produced in large quantity are much more valuable than a single, large bloom.

Many members of the Apiaceae (formerly known as Umbelliferae) family are excellent insectary plants. Fennel, angelica, coriander, dill, and wild carrot all provide in great number the tiny flowers required by parasitoid wasps. Various clovers, yarrow, and rue also attract parasitoid and predatory insects. Low-growing plants, such as thyme, rosemary, or mint, provide shelter for ground beetles and other beneficial insects. Composite flowers (daisy and chamomile) and mints (spearmint, peppermint, or catnip) will attract predatory wasps, hover flies, and robber flies. The wasps will catch caterpillars and grubs to feed their young, while the predatory and parasitoid flies attack many kinds of insects, including leafhoppers and caterpillars.

Of course, you also may plant species that are not noted for harboring beneficial insects. There is no rule that says an insectary border must be limited to insectary plants.