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Saw-toothed grain beetle

1. Saw-toothed grain beetle adults ©Nigel Cattlin/FLPA.
2. Saw-toothed grain beetle adult ©Nigel Cattlin/FLPA.

Identification

The adults are 2.5-3.5 mm long, dark brown in colour and with 6 teeth along each side of the prothorax (hence the name 'saw-toothed').

Symptoms

The larvae feed on the germ (embryo part of the seed) of damaged and broken grains (the supply of which increased with the advent of the combine harvester), so they can be regarded as secondary pests, and grains which are entire are less vulnerable to attack. Relatively small numbers of insects can rapidly give rise to serious infestations. They are small, active insects which readily exploit cracks and crevices where they can hide.

Life-cycle

The female saw-toothed grain beetle lays up to 400 eggs, either singly or in small batches, at a rate of 6-10 per day. These are laid in, or adjacent to, a suitable food supply and at a temperature of 20-23 C hatch in 8-17 days to give flattened larvae about 0.9 mm long. They are yellowish/white in colour, with brown flecks and a brown head. Typical of coleopterous larvae, they have a well-developed head, biting mouthparts and 3 pairs of legs on the thoracic segments. The larval stage lasts 4-7 weeks during which the larvae go through 2-5 moults, attaining a length of 3 mm. They then construct a cell of food particles and other debris in which to pupate, emerging after 1-3 weeks as adults. On emergence the adult beetles live for 6-10 months, breeding within a temperature range of 17.5-40 C. At 20 C the full life-cycle is completed in 12-15 weeks whilst at 32-35 C it takes only 20 days. Although they originate from tropical climates, they are sufficiently cold-hardy to be able to overwinter in crevices in unheated buildings.

Importance

The saw-toothed grain beetle is now the primary insect pest of grain stores in the UK (movement on imported and exported foodstuffs has contributed to the international population spread). They also infest processed cereal products, dried fruit, dried meats, oilseeds, nuts and rice. When infestations in stores become heavy they cause the grain to heat. This in turn leads to caking, moulding and even sprouting. Both the quality and weight of the grain may be reduced. Malting barley may be rejected because of poor germination, whilst milling wheat is adversely affected by tainting and discoloration. In grain, the mere presence of insects may result in rejection.

Management of storage pests

 

 

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