Benefits and Value of Insects
(Master Garden Products)
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.
