Photo 1. Diadegma seeking its host. Photo 2. Diadegma has located a second stage
diamondback moth caterpillar.
Photo 3. Diadegma laying an egg in a second
stage diamondback moth caterpillar.
Photo 4. Diadegma wasp preening or cleaning
its body after egg laying.
Photo 5. The pupa of diamondback moth,
yellowish and about 8 mm long. It is blunt at
one end and tapered at the other.
Photo 6. Pupa of Diadegma. The pupa if the
diamondback moth is destroyed by Diadegma,
except for the silken cocoon. The Diadegma
cocoon is about the same size as that of the
diamondback moth. They are pink/cream, then
dark brown.
Photo 7. Pupa of Diadegma becomes dark
before emergence of the adult. It is eliptical
(egg-shaped) not tapered, and the diamondback
moth skin is at one end.
Pacific Pests and Pathogens - Fact Sheets Pacific Pests and Pathogens - Fact Sheets
Biocontrols - Diadegma (285)Biocontrols - Diadegma (285)
Common NameCommon Name
Parasitic wasp
Scientific NameScientific Name
Diadegma semiclausum, an ichneumonid (previously known as Diadegma euerophaga, Diadegma xylostellae,
Angita cerophaga).
DistributionDistribution
Worldwide. Diadegma semiclausum is native to Europe, but has been introduced into many countries in Asia, Africa
and Oceania. It is established in Australia and New Zealand but, it has not established in other Pacific islands, with
the exception of the highlands of Papua New Guinea. The wasp has also been introduced into the highlands of
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India, Indonesia, Laos, Malaysia, the Philippines, Taiwan, Thailand, and Vietnam. In tropical countries, it does not
survive below about 800 m.
PreyPrey
Diamondback moth, Plutella xylostella.
Symptoms & Life CycleSymptoms & Life Cycle
Diadegma is most commonly found parasitising diamondback moth, although it has been reared from other
species. It is a larval parasitoid, preferring to lay its eggs in small larvae, those that have just left their egg masses
on Brassica leaves.
When the wasp approaches (Photos 1&2), the moth larvae may react with jerky movements, or drop from the leaf
on silken threads to escape attack. Those that remain become the target of the wasp which quickly inserts a
single egg into each larva (Photos 3&4). The larvae are parasitised once only as the wasp can tell if the
diamondback moth larvae have already been attacked.
Parasitised moth larvae develop normally, and outwardly look the same as those that are unparasitised. However,
when the moth develops a cocoon (Photo 5), the larva of the wasp makes its own cocoon inside and then develops
into a pupa (Photo 6). After 8-10 days the adult emerges.
The life cycle of Diadegma is 18-20 days. The female wasp can live for about 25 days if a suitable sugar food is
available. During that time it can lay many hundreds of eggs.
The parasitoid prefers temperatures in the range 15-25oC. Therefore, in tropical countries it is most abundant in
the cooler highlands.
ImpactImpact
Diadegma is a very effective natural enemy of diamondback moth, and very high rates of parasitism (>90%) often
occur, provided that broad-spectrum insecticides are not used.
Detection & InspectionDetection & Inspection
Look for the small black wasps flying between brassica plants, often hovering near leaves damaged by diamonback
moth larvae. Chemicals from the damage attracks them. Look for the wasps searching for diamondback
moth larvae on the leaves. Look for Diadegma pupae which are formed inside the silken nets spun by the
diamonback moths when they pupate. Diadegma pupae are oval-shaped, whereas those of diamondback moth are
tapered at one end.
Management as Biocontrol AgentsManagement as Biocontrol Agents
Diadegma is very sensitive to broad-spectrum insecticides, such as pyrethroids and organophosphates. They
should not be used if the wasp is active in the crop, otherwise they will kill the wasp and make control of
diamonback moth difficult. Instead, if an insecticide is required, use Bt, Baccilus thuriengensis, or another selective
insecticide. Together, Diadegma and Bt can form the basis of an effective IPM program for diamondback moth.
AUTHORS Mike Furlong and Grahame Jackson
Photos 1-6 Mike Furlong, University of Queensland, Brisbane, Queensland.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of
sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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