Indigenous predators and parasites

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Wild birds

It has been shown that a pair of blue tits can consume 10 000 caterpillars and one million aphids in a 12 month period. The installation of tit boxes is a worthwhile activity. Wrens, thrushes and blackbirds similarly contribute to the control of garden insects.

Hedgehogs

Hedgehogs belong to the insectivore group of mammals, but are omnivorous. Although their preferred diet is insects (up to 200 g per day) they will eat slugs. Care must be taken that they are not exposed to dead slugs which have consumed slug bait containing methiocarb or methaldehyde, as these would be toxic to the hedgehog. Hedgehogs are encouraged to enter gardens by means of small holes cut into the base

Biological control is the use of natural enemies to reduce the damage caused by a pest (or disease).

of a fence panel. Within gardens, heaps of logs and piles of leaf litter in a quiet location are suitable for their daytime and overwintering retreat. Wooden hedgehog shelters are commercially available.

The black-kneed capsid

The black-kneed capsid (Blapharidopterus angulatus) is an insect found on fruit trees alongside its pestilent relative, the common green capsid. It eats more than 1000 fruit tree red spider mites per year. Its eggs are laid in August and survive the winter. Winter washes used by professional horticulturalists against apple pests and diseases often kill off this useful insect. The closely related anthocorid bugs, such as Anthocoris nemorum, are predators on a wide range of pests, such as aphids, thrips, caterpillars and mites, and have recently been used for biological control in greenhouses.

Lacewings

Lacewings, such as Chrysopa carnea, lay several hundred eggs per year on the end of fine stalks, located on leaves. Several are useful horticultural predators, their hairy larvae eating aphids and mite pests, often reaching the prey in leaf folds where ladybirds cannot reach.

Ladybird beetle

The 40 species of ladybird beetle are a welcome sight to the professional horticulturist and lay person alike. Almost all are predatory. The red two-spot ladybird (Adalia bipunctata) emerges from the soil in spring, mates and lays about 1000 elongated yellow eggs on the leaves of a range of weeds, such as nettles, and crops such as beans, throughout the growing season. Both the emerging slate-grey and yellow larvae and the adults feed on a range of aphid species. Wooden ladybird shelters and towers are now available to encourage the overwintering of these useful predators.

A worrying development in the last few years has been the rapid spread and increase of the harlequin ladybird from South-East Asia. This species is larger (6-8 mm long) and rounder than the two-spot species (4-5 mm). It has a wider food range than other ladybird species, consuming other ladybird's eggs and larvae, and eggs and caterpillars of moths. Furthermore, it is able to bite humans and be a nuisance in houses when it comes out of hibernation.

Carabid beetles

The ground beetle (such as Bembidion lampros), a 2 cm long black species (see Figure 16.5), is one of many active carabid beetles that actively predates on soil pests such as root fly eggs, greatly reducing their numbers.

Hoverflies

Superficially resembling wasps, these are commonly seen darting or hovering above flowers in summer. Several of the 250 British species, such as Syrphus ribesii, lay eggs in the midst of aphid colonies, and the legless light-green coloured grubs consume large numbers of aphids.

British Hoverflies

Figure 16.5 (a) Predatory ground beetle (b) Ichneumon wasp parasitic on caterpillars

Dacnusa Sibirica

Figure 16.5 (a) Predatory ground beetle (b) Ichneumon wasp parasitic on caterpillars

The flowers of some garden plants are especially useful in providing pollen for the adults and therefore encouraging aphid control in the garden. Summer flowering examples are poached-egg plant (Limnanthes douglasii), baby-blue-eyes (Nemophila menziesii) and Californian poppy (Romneya coulteri). Later summer and autumn examples are Phacelia tanacetifolium and ice plant (Sedum spectabile).

Mites and spiders

Predatory mites such as Typhlodromuspyri eat fruit tree red spider mite and contribute importantly to its control. The numerous species of web-forming and hunting spiders help in a very important but unspecific way in the reduction of all forms of insects.

Wasps

The much maligned common wasp (Vespula vulgaris) is a voracious spring and summer predator on caterpillars, which are fed in a paralyzed state to the developing wasp grubs. Digger wasps also help control caterpillar numbers and benefit from dead hollow stems of garden plant which they use as nests all year round.

There are about 3000 parasitic wasp species of the families Ichneumonidae, Braconidae and Chalcidae found on other insects in Britain. Ichneumons (Opion spp. see Figure 16.5) lay eggs in many moth caterpillars. The braconid wasp (Apanteles glomeratus) lays about 150 eggs inside a cabbage white caterpillar and the parasites pupate outside the pest's dead body as yellow cocoon masses. The chalcid (Aphelinus mali) parasitizes woolly aphid on apples.

The spiracles of insects provide access to specialized parasitic fungi, Figure 16.6 Swollen aphid parasitized by particularly under damp conditions. In some years, aphid numbers tiny wasp are quickly reduced by the infection of the fungus Entomophthora aphidis, while codling moth caterpillars on apple may be enveloped

Pictures Anagrus Spp

by Beauveria bassiana. Cabbage white caterpillar populations are occasionally much reduced by a virus, which causes them to burst.

Increased attention is being given by horticulturalists to the careful selection of pesticides (if they are needed) to avoid unnecessary destruction of indigenous predator and parasite numbers (see also p271).

In recent years, commercial firms have begun to make available ready-to-use products containing indigenous predators or parasites to outdoor growers. Examples are two-spot ladybird, lacewing larvae and three nematode parasites (against slugs, vine weevil larvae and flea beetles (see also Table 16.1).

Table 16.1 Biological control organisms reared commercially for use in horticulture

Pest or disease

Crop

Control

Type

Aphids

G

Aphidoletes aphidimyza

Midge

G

Aphidius spp.

Wasp

Ch

Verticillium lecani

Fungus

Caterpillars

B

Trichogramma brassicae

Wasp

G

Bacillus thuringiensis

Bacterium extract

Flea beetle

B

Howardula phyllotreta

Nematode

Glasshouse whitefly

T

Macrolophus caliginosus

Anthocorid bug

G

Encarsia formosa

Wasp

Leaf miner

T, C, F

Dacnusa sibirica

Wasp

T, C, F

Diglyphus isaea

Wasp

Leaf hopper

T

Anagrus atomus

Wasp

Mealy bug

G

Cryptolaemus montrouzieri

Ladybird

G

Leptomastix dactylopii

Wasp

Red spider mite

G

Phytoseiulus persimilis

Mite

G

Amblyseius calfornicus

Mite

G

Feltiella acarisuga

Midge

T, C, F

Therodiplosis persicae

Midge

Sciarid fly

G

Steinernema feltiae

Nematode

G

Hypoaspis miles

Mite

G

Bacillus thuringiensis strain

Bacterial extract

Silver leaf fungus

Tf

Trichoderma viride

Fungus

Slugs

G

Phasmarhabditis hermaphrodita

Nematode

Thrips

C, F, P

Neoseiulus cucumeris

Mite

C, F

Orius laevigatus

Anthocorid bug

Tomato mosaic virus

T

mild strain of virus

Vine weevil

G

Steinernema capsicarpae

Nematode

Key; B: brassicas; T: tomato; C: cucumber; P: sweet peppers; F: flowers; Tf: top fruit; Ch: chrysanthemum; G: general use.

Key; B: brassicas; T: tomato; C: cucumber; P: sweet peppers; F: flowers; Tf: top fruit; Ch: chrysanthemum; G: general use.

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Responses

  • juan delgado
    How to control ichneumon?
    8 years ago

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