Etiella behrii (lucerne seed web moth)

Photograph of a Seed web moth on a leaf
Lucerne seed web moth at rest on plant material. Photo: J. Wessels.
Image of seed damage caused by etiella moth larvae
Seed damage caused by larvae of the Etiella moth (lucerne seed web moth). Photo: J. Wessels.


General information

In summer pulses, lucerne seed web moth larvae complete their development in a single pod before escaping through a characteristic pinhole-sized exit (2-3 mm diameter). In peanuts, many newly hatched larvae move down the plant and seek out the pods, which are below ground. The majority of pod-seeking larvae reach the pods within 24 hours of egg hatch.

                                       
Scientific name

Etiella behrii

Description

The moths are small (12 mm long at rest, with a 20-22 mm wingspan) and distinctively coloured. They are grey-brown with a distinctive stripe along the leading edge of each forewing and an orange band on each forewing (about one quarter of the distance along each forewing from its base). Hindwings are pale grey. The wings are folded back along the body when resting.

   

Moths have a prominent ´snout´ (formed by the labial palps), that is typical of pyralids. The eggs are small (0.6 mm diameter), cream and flattened. Small larvae may be cream or pale green, with no stripes and a dark head. Mid-sized larvae may be pale green or cream, with pale brown or reddish stripes. Larger larvae are characteristically green with pink or reddish stripes and a brown head. Larvae in the pre-pupal stage can be aqua blue or dark pink with no stripes.

Similar species

Moths may be confused with those of other non-pest Etiella spp. which feed on rattle pods. Webbing made by etiella larvae at the base of peanuts may be confused with that made by the (darker) larvae of Endotricha puncticostalis and Lecithocera sp. Both are very common but are of no consequence.

Distribution

Etiella behrii is found over much of South-East Asia, including China, Indonesia, the Pacific Islands and all of Australia, including Tasmania.

Crops attacked

Soybean, mungbean, navy bean, azuki bean, lucerne. Important pest of peanuts, especially in drier areas, and of specialist legumes (e.g. natto soybeans). Associated with aflatoxin in peanuts. Rattle pods are favourite weed hosts.

Life cycle

Eggs are laid on pods and flowers or under bracts and are very hard to detect. In most legumes with above-ground pods, newly-hatched etiella larvae bore straight into pods leaving a near-invisible entry hole. In peanuts, the lifecycle can be completed in four weeks at 30°C.

Risk period

Crops may be infested from flowering onwards, but are at greatest risk during late podding. Peanuts are at particular risk during end-of-season droughts when the dry soil allows larval access to the pods. Such conditions also favour the development of aflatoxin in pods with etiella exit holes.

Damage

Because etiella larvae consume far less than larger caterpillar species such as Helicoverpa, seeds are usually only partially eaten out, often with characteristic pin-hole damage. This damage is difficult to grade out and its unattractive appearance reduces seed quality. Larval frass adhering to damaged mungbean seeds is frequently mistaken for bruchid eggs. However unlike bruchids, etiella are unable to infest stored seed.

   

In peanuts, etiella damage is a major aflatoxin risk factor. This highly carcinogenic toxin is produced by an Aspergillus fungus, which gains entry to pods through holes (2-3 mm diameter) made by exiting etiella larvae, but not through the very much smaller entry holes (0.2-0.3 mm diameter). Etiella-damaged pods can have aflatoxin levels 100 times greater than undamaged pods. Etiella infestations initiated close to harvest can result in the post harvest emergence of larvae as peanut pods dry down in storage.

   

Pod damage in peanuts is most likely in drought years as soil moisture inhibits larval movement in the soil. Larval movement is assisted by cracks in dry soils.

Monitoring and control

Techniques are being developed to monitor moth activity with light traps or lures. Etiella behrii is most vulnerable at the moth stage. No pesticides are registered.

Cultural control

Late irrigations reduce the risk in peanuts by wetting up the surface soil.

Further information

  • Crop Insects: The Ute Guide Northern Grain Belt
  • Pests of Field Crops and Pastures: Identification and Control. Editor: P.T. Bailey.

Last updated 22 June 2010