Organic Gardening – Benefits of Garden Insects

Know your friends

Although you should encourage a whole range of wildlife into your organic garden, creatures that are predators of garden pests are particularly welcome. It is important to be able to recognize these creatures and know something of their habits and lifecycle, because this can help you tip the balance between friend and foe in your favour, and is an important part of organic pest control.

Organic Gardening - Benefits of Garden Insects Some predators have a limited diet and target specific pests: hoverfly larvae, for exam ple, feed mainly on aphids. Others are less discerning: centipedes and hedgehogs, for example, are among those which feed on a wide range of grubs, insects and eggs, some of which are pests, some of which are not. However, because their diet will consist of what is most available, they will eat more pests during a pest outbreak, and thus they still help to restore the natural balance in the organic garden.

The first step in encouraging any of these creatures is to stop using pesticides — some predators are sensitive even to organic sprays. The second step to take is to increase the wildlife value of your garden. In addition, knowing the habits of some of the most useful garden friends means you can artificially boost their populations. As well as putting up nest boxes for birds, for example, you can put up boxes in which bats can roost and even “refuges” in which lacewings can overwinter.

Sometimes the dividing line between friend and foe is not clear-cut. Earwigs, for example, can be pests if you have prize dahlias, but they can help by preying on aphids and codling moth eggs. Blackbirds stop at nothing to get at ripe strawberries, but they also eat caterpillars, and even wasps feed their young on small insect pests. The best strategy is to tolerate such creatures and protect vulnerable crops when necessary.

Below is a description of the most beneficial insects commonly found in the organic garden. As a general rule, check when you come across something you do not recognize — certainly before you squash it! The larvae of ladybirds and hoverflies, for example, can easily be mistaken for harmful grubs.


Insects

Ladybirds

Appearance

Adult beetles have red and black or yellow and black markings — but most commonly red with black spots. Larvae have tapering bodies which are segmented, greyish-black with orange markings; these insects are active from late spring to mid-summer.

Usefulness

Both adults and larvae feed mainly on greenfly, but also eat other pests including mites, scale insects, mealy bugs and small caterpillars.

To encourage them

Cultivate a nettle patch for early aphids and tolerate some aphids around the garden for ladybirds to feed on. Do not do too much tidying up in the garden during autumn: leave some dry plant debris, loose bark and hollow stems to provide hibernation site for these insects. Avoid using pesticides.


Hoverflies

Appearance

Adults resemble small wasps or bees but they have only one set of wings. Their flight is characteristic: darting then hovering motionless as they visit flowers in summer and autumn. The legless larvae are generally translucent brown or green, appearing from late spring onwards.

Usefulness

The larvae of many species (about 100) feed on aphids, eating them at a significant rate — sometimes up to as much as 50 a day. They also eat fruit tree spider mites and small caterpillars.

To encourage them

Grow flowers that attract adult hoverflies by providing nectar and pollen for them to feed on. Tolerate some aphid colonies as sites for adults to lay eggs. Avoid using pesticides.


Lacewings

Appearance

The most commonly seen species of lacewing is green, with two pairs of flimsy wings and large eyes. The larvae are small, bristly and active, variable in colour but often a creamy-brown, appearing from late spring to mid-autumn. Sometimes these insects fix the skins of sucked-out aphids on to the bristles on their backs to act as camouflage.

Usefulness

Both adults and larvae feed on aphids. The larvae also eat mites, leafhoppers, scale insects and caterpillars.

To encourage them

Grow flowers to attract adults, which also feed on nectar. Make lacewing “refuges” to encourage them to overwinter in the garden. Avoid all pesticides, even organic ones.


Ground beetles and Rove Beetles

Appearance

These are dark scuttling beetles with long legs and antennae; few of them fly. Rove beetles tend to be longer and thinner than ground beetles, more like oversized earwigs. They are seen all year round.

Usefulness

Both types of beetle are important predators of slugs. They also eat the eggs and larvae of cabbage and carrot root flies and lettuce root aphids.

To encourage them

These beetles live in the soil or under debris, logs and stones — anywhere that it is moist and shady. Leave the soil undisturbed where possible, and use mulches and ground-cover plants. Put down shelters such as old tiles or pieces of wood. Avoid using pesticides.


Centipedes

Appearance

Centipedes are long, segmented, fast-moving creatures with many legs, distinguished from millipedes by the fact that they have only one pair of legs per segment (whereas millipedes have two). Most garden species are yellow or brown.

Usefulness

They often prey on slugs and snails, although a range of insects is also included in their diet.

To encourage them

Some species live in the soil, others under logs and stones. Encourage them as for ground beetles.


Earwigs

Appearance

Dark brown in colour, flattish, slender insects with a prominent pair of pincers at the rear.

Usefulness

These insects cause some damage, often to flower buds and petals, but they make up for this by eating caterpillars, large numbers of aphids and insect eggs, particularly those of the codling moth.

To encourage them

Earwigs like to rest during the day in narrow crevices — in loose bark or old seedheads, for example. If you find them in flowerheads or curled round an apple stalk, the chances are that they are taking refuge rather than doing damage.

If you want to keep these insects away from your dahlia or chrysanthemum plants, provide alternative night-time accommodation in flowerpots stuffed with straw fixed upside down among the flowers, then release the earwigs well away from the flowers anytime in the morning.


Anthocorid bugs

Appearance

These are small, reddish to dark brown, beetle-like creatures with a sharp snout. They are active from late spring to early autumn.

Usefulness

They feed mainly on aphids, but also eat scale insects, capsid bugs, caterpillars, mites and blossom weevil larvae.

To encourage them

They overwinter under bark and in leaf litter, so will be more likely to be found in gardens with trees and hedges. Avoid using pesticides.


Aphidoletes

Appearance

Aphidoletes are tiny delicate midges with long antennae. The larvae are orange with no legs, and are just visible to the naked eye. They are active from late spring to early autumn.

Usefulness

The larvae eat aphids.

To encourage them

Grow nursery plants for aphids.


Black-kneed capsid

Appearance

These greenish beetle-like bugs have overlapping wings and long antennae. The knee-joints are black, distinguishing them from other species, some of which are pests.

Usefulness

They are a major predator of fruit tree red spider mites; they also eat greenfly, thrips, leafhoppers and small caterpillars.

To encourage them

Never use winter washes on fruit trees, and avoid all pesticides (even organic ones) as capsids are extremely sensitive to them.


Ichneumons

Appearance

Ichneumons are leggy brown insects with a wasp-like waist. They are one of the several groups of parasitic wasps found in the garden.

Usefulness

They parasitize the caterpillars of butterflies and moths.

To encourage them

Grow attractant flowers.


Making a lacewing refuge

Cut the bottom off a large (1 or 2-litre) plastic drink bottle. (Do not wash it out — the remains of any sugary solution is an added attraction.) Cut a piece of corrugated cardboard 82-100cm (32-40in) long to fit the height of the bottle, roll it up and push it inside. Make two tiny holes in the base of the bottle and push a piece of thin wire through to secure the cardboard. Tie a piece of string round the neck of the bottle so that you can suspend it from a fence or tree branch. Leave the top on to keep out rain.

27. January 2011 by Dave Pinkney
Categories: Organic Gardening | Tags: , | Comments Off on Organic Gardening – Benefits of Garden Insects

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