Grain moth

Sitotroga cerealella

Crop: Stored grain, especially maize

Why is it a problem? The grain moth is an important pest of whole cereal grains, especially maize. It destroys the inside of grains, resulting in weight loss.

Where and when is it a problem? Grains moths are less widespread than grain weevils. They tend to be most prevalent above 900 m asl and below 1,700 m. Maize can be safely stored for many years above 2,400 m asl.

IDENTIFICATION

Grain moth

Adult moths are small (5-7 mm long, wingspan 10-16 mm) and pale brown. Larvae are rarely seen as they complete their development within a single grain. The final-instar larva spins a silken cocoon in which it turns into a reddish-brown pupa.

SYMPTOMS

Feeding damage is hidden within the grain. However, just before pupation, the larva constructs a chamber just below the grain seed coat, forming a small, circular, translucent ‘window’. On emergence the adult pushes the window open, leaving a small but characteristic, round hole, usually in the crown end of the grain. Part of the window often remains at the edge of the hole in the form of a ‘trapdoor’ or shallow cone.

Confusion with other pests: A range of pests can damage stored grain, sometimes at the same time. Adult grain moths, and the form of the emergence holes, are characteristic. The other major stored grain pest of maize is a grain weevil.

BIOLOGY

Lifecycle: Attack of grains can start in the field. Eggs are laid on the outside of grains, in cracks, grooves or holes made by other insects. Adults live for up to 15 days. On hatching larvae bore into the grain, completing their development within a single grain. Just before pupation the larva will extend a chamber to just beneath the surface of the grain, forming a small circular “window” of translucent seed coat. This is the first visible sign of infestation. In very small grains (e.g. some sorghum grains), pupation may occur between two or more grains held together by the silken threads of a thin cocoon. Two or three larvae can complete their life cycle within a single maize grain. Several generations can be completed in a year under the right conditions. In temperate areas they overwinter as larvae.

Dispersal: Adults are strong fliers and cross-infestation occurs easily. However, they cannot penetrate far into closely packed grain. As larvae also stay in the same grain throughout their development, infestations in bulk grain are usually confined to the outermost exposed layers.

When can damage be expected? The grain moth tends to most prevalent between about 900 m asl. and 1,700 m asl. It is generally less common than grain weevils.

Hosts: The grain moth has been reported from a wide range of cereals, as well as other crops. However, in Bhutan it is only recognized as a serious pest of maize.

MANAGEMENT PRACTICES

Seed losses to pest insects within storage can be minimized through good management practices, including the use of modern storage techniques.

Monitoring

Monitoring throughout the storage period is necessary to ensure that pest insect populations, and moulds, are not building up to unacceptable levels. Inspect a random sample seeds or cobs for evidence of seed damage and pest presence. Note that larval stages won’t be evident as development occurs entirely within the grain.

Effect of variety

Varietal differences is significant for some crops, but this has not been studied in Bhutan.

Non-chemical management

See grain weevils.

Chemical management

Insecticides are not needed as there are more effective, safer options available such as Super grain bags (see brochure or video).

 

Version: NPPC 2017. Grain moth V1.0. Bhutan Pest Factsheet. www.PestsofBhutan.nppc.gov.bt. Date produced: 14 April 2017. Contact: nppcsemtokha@gmail.com

Image acknowledgements: Clemson University-USDA Cooperatives Extension Slide Series, Bugwood.org

 

 

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