Sitotroga cerealella (Olivier).
Common name: Angoumois grain moth.
Geographical distribution: Cosmopolitan, more abundant in warmer regions.
Morphology: The larvae (caterpillars) are initially reddish, then becoming white, with a brown head, 5-7 m long. Adults brown-gray, about 4-7 mm long, forewings narrow, gray, pointed apically, with small dark spots, hindwings silvery, with a pale fringe.
Host plants: Cereal grains, especially wheat, barley and corn.
Life cycle: Each Female lays 100-180 eggs on cereal seeds, which the hatching larvae enter immediately. They feed on one or more grains and pupate therein, leaving a typically round hole. The moth lives for 1-2 weeks and may complete 5-6 annual generations.
Economic importance: The larvae feed on and burrow in stored grains, damaging as many as 25-60% of wheat seeds, 10-15% of barley; half of such seeds do not germinate. Major chemical and physical properties of the stored wheat are affected, including a very large increase (>100%) in the amounts of reducing and non-reducing sugars, and a decrease in the starch, total protein, wet and dry gluten contents. During spring the pest may also oviposit on growing cereals in the field, the larvae completing their development in the stores. The emerging adults can then initiate infestations, bringing about continuous damage. Heavy injury is caused mostly to the upper layers of stored grains, as the pest does not penetrate deeper into the bulk.
Monitoring: The presence of typically round holes, and of flour dust, indicate the presence of the pest. This can also be determined within grains by acoustically detecting the internal-feeding larvae, 2-3 weeks after oviposition. Adults can be trapped using food-bait and pheromone traps.
Mating disruption: Disruption by a pheromone source resulted in a 20-30% reduction in the proportion of mated females.
Cultural methods: Late planting and early harvest can reduce pre-harvest losses. Methods of reducing humidity in grain stores such as plastering the walls with mud or using sealed containers may reduce or minimize damage. Periodic inspections and removal of infestations can be effective, especially if the grain is closely packed so that pest attacks are limited to the outermost layers.
Plant resistance: Resistant varieties of maize millet, rice and wheat have been developed in many parts of the world.
Irradiation: Gamma radiation of the pupae at 32°C reduced fecundity and egg hatching, and retarded growth of the larvae of the F1 progeny.
Chemical control: Standard fumigation with phosphine and treatments with insecticides like organophosphates, pyrethroids and spinosad can be effective, but the pest has developed resistance to some insecticides in several parts of the world. Other chemicals tried are edible oils, like soya bean oil and cotton seed oil and agricultural waste materials, extracts of various plants, like spearmint, cottonseed and eucalyptus and the toxins of Bacillus thuringiensis (BT).
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