Insect pests of vegetable brassicas in Western Australia

Page last updated: Tuesday, 26 October 2021 - 7:20am

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Beneficial natural control agents

For diamondback moth

Diadegma wasp stinging diamondback moth larva
Figure 44 Diadegma wasp stinging diamondback moth larva
Diadegma wasp cocoon on brassica leaf
Figure 45 Diadegma wasp cocoon

Diadegma, a wasp parasite of diamondback moth larvae, is the most abundant of the natural control agents for this pest. Once the wasp parasite larva completes its development inside the diamondback larva, it emerges to spin a cocoon within the silken case produced by the host diamondback moth larva.

Small apanteles wasp showing long antennae
Figure 46 Apanteles wasp
Small white cocoon of apanteles wasp
Figure 47 Apanteles parasite cocoon

Apanteles, another species of wasp parasite that attacks diamondback moth larvae, is also abundant. The wasp larvae pupate in small white cocoons.

Diamondback moth grub infected with fungus Zoophthora radicans disintegrating on the leaf
Figure 48 Parasitic fungus of Diamondback moth

A fungus, Zoophthora radicans can kill larvae and pupae. Infected larvae disintegrate on the plant. Mass larval deaths from this fungus occur in moist conditions and where larval density is high.

For cabbage white butterfly

Grubs of parasite emerging from cabbage white butterfly pupa
Figure 49 Cabbage white butterfly pupa showing grubs of a wasp parasite
White cocoon of a wasp parasite of cabbage white butterfly
Figure 50 Cocoon of wasp parasite of cabbage white butterfly pupae

Grubs of a wasp parasite of cabbage white butterfly emerge from a cabbage white butterfly pupa (Figure 50). These wasp grubs then spin white cocoons (Figure 51). The adult wasp chews a hole in the cocoon and emerges.

For aphids

 

Aphid wasp parasitising green peach aphid
Figure 51 Aphid wasp parasite

Wasp parasites help keep aphid numbers in check. The wasp completes the larval stage of its life cycle within the aphid body producing an aphid ‘mummy’ from which the adult wasp cuts an emergence hole.

Orange and black adult predator ladybird
Figure 52 Predatory ladybird adult

Predatory ladybird adults are usually brightly coloured orange and yellow with black stripes. Adults are around 7mm long.

Cluster of orange ladybird eggs on brassica leaf
Figure 53 Predatory ladybird egg cluster

Predatory ladybird eggs are bright yellow and are laid in groups.

Predatory ladybird grub showing characteristic colour of grey with yellow bands
Figure 54 Predatory ladybird grub

Predatory ladybird larvae are common predators of aphids as well as eggs and young stages of other insect pests. They are 8–10mm long and grey with yellow bands.

Adult hover fly showing characteristic black and yellow striped abdomen
Figure 55 Hover fly

Adult hover flies are about 10mm long with a black and yellow striped abdomen. Adults are not predatory.

Small orange hover fly maggot on brassica leaf
Figure 56 Hover fly maggot

Hover fly maggots are predators of aphids.

Aphid turned orange following fungal disease infection
Figure 57 Fungal disease of aphids

A fungal disease can kill aphids. The disease is normally only seen in the more humid conditions of spring.