Weevil Control

Grain Weevil and Rice/Maize Weevil

The Grain Weevil

Grain weevil is well established in the UK as a pest of whole cereal grain, sometimes hard cereal products. Not other stored foods. Larvae live totally within grains. Survive winter in the UK but not breed below 13 degrees Celsius.

Grain Weevil Distribution and Habitat

The grain weevil is essentially an indoor pest of grain and hard cereal products, the grain weevil is common throughout the temperate and slightly warmer parts of the world, but not in the tropics. It has been established in Britain for centuries, even being found in Roman granary excavations, as a primary pest of all grain storage buildings.

Rice Weevil (Sitophilus oryzae), and Maize Weevil (Sitophilus zeamais) are two almost indistinguishable species of tropical weevils commonly found in Britain. Both are distinguished from the grain weevil by being less shiny and having 4 more-or-less distinct orange patches on the wing cases (elytra). The life cycles are very similar to that of the grain weevil, though the minimum breeding temperature is around 17 degrees Celsius, at which the life cycle takes about 13 weeks. Both species are frequently imported into Britain and occur within the British grain trade with some frequency. They also occur fairly commonly within the processed food industry and their origin here may well be due to unseen or hidden infestations in imported rice, maize and possibly other stored cereals.

To distinguish between these two species necessitates microscopic dissection but is practically unimportant because they have such similar habits and are of equal pest status. Both species can fly, but the maize weevil does so more readily when temperatures are sufficiently high.

Control of Rice/Maize Weevils – Control measures are the same as for the grain weevil and ‘exposed’ infestations of wandering adults are relatively easy to control if the adults are denied access to ‘new’ foodstuffs suitable for egg-laying.

Wood-boring Weevils, Pentathrum huttoni and Europhryum confine, are two similar species of dark brown weevils, approximately the same length as the Grain, Rice and Maize Weevils (2.5 to 4.5mm) but generally slimmer in appearance. The former occurs through most of Britain and is seemingly restricted to the southern half. Both attack wood that has already been damaged by fungal activity. Eggs laid in the timber by the female hatch into typical weevil larvae – stout, curved and pearly white. They may take 6 to 8 months to reach full size and then pupate within the timber, the adults emerging 2 or 3 weeks later.

Adult wood-boring weevils can live for considerable periods (maybe 15 months) and seem most commonly to occur in basements, cellars and other sub-ground floor areas of buildings where the timber has most frequently been subjected to damp and fungal rot. They are far less common than the common furniture beetle, although the emergence holes are similar in size and shape.

Control of Wood-boring Weevils

Small areas of infested wood, e.g. around domestic sinks, can be removed and replaced with sound new wood and a local residual insecticide treatment carried out. Larger structural timbers will generally require treatment by professional timber treatment specialists.

Action should be taken to avoid re-infestation by keeping areas dry and not allowing wood to remain damp for long periods.