WEEVILS

The Grain weevil (Sitophilus granarius) can only breed in grain with a moisture content of more than 9.5 % and at temperatures within the range  13 - 35 °C. The female lays about 200 eggs at a rate of 2 - 3 per day depending upon temperature and humidity, placing each one in a small hole bored in the grain and sealing it in with a mucilaginous plug of  saliva. At 18 - 20 °C the eggs hatch in 8 - 11 days to give  small, white, legless larvae which feed on the endosperm of the grain.  Only one larva develops in small grains such as wheat  and rice but large grains such as maize will support the development of several. Larvae are never free-living  and develop entirely within the grain. They moult four times, finally pupating within the grain after 6 - 8 weeks. The adults emerge after a further 5-16 days and will live for about 9 months. If disturbed they will feign death by drawing their legs up to their bodies and remaining still. At 15 °C and a grain moisture content of 11.3% the full    life- cycle takes 6 months. The life-cycles of the Rice and Maize weevils (Sitophilus  oryzae & Sitophilus  zeamais respectively) follow a similar course to that of the Grain weevil. Grain weevils  are  frequently  regarded  as  primary pests  of  grain  since  they  are able to infest otherwise undamaged grain. They will however also attack other hard cereal products, e.g. macaroni and spaghetti. Fine cereal products are unsuitable for breeding purposes unless they become caked. The Maize weevil will breed on maize in the field, but the Rice weevil only breeds in stored grain.

STORED PRODUCT MOTHS

The Mediterranean Flour Moth (Ephestia kuehniella) is a particular problem in provender mills, bakeries and occasionally even in catering premises. One generation is usually produced, but in warm conditions adults will be present  throughout the year when there may be 4 - 6 generations.  Mating takes place  immediately after the adults emerge. Up to 350 eggs are laid and these may be stuck to various foods by a sticky secretion. The eggs hatch in 4 - 28  days to  give  white  or pinkish larvae and spin silken tubes in which they live. After 3 - 5 moults the larvae are full grown and 15 - 19mm long. They then wander away  from food and pupate for 7-16 days in the dark corners of buildings or machinery. In temperate climates these moths overwinter as larvae but, in contrast to other species, usually remain in the foodstuff. Moth larvae can cause considerable  damage to stored goods by feeding or by contamination with their own products,  e.g. webbing and frass. Adult insects are not responsible for damage as  they either feed on liquid food and water or do not feed at all. The larval by-products, webbing and frass, are a particular problem. Webbing   can entirely coat commodities and may be responsible for blocking machinery and ducts. The problem is exacerbated when webbing becomes mixed with  frass, food and general debris. Larval webbing of the Mediterranean Flour Moth can cause serious blockages in provender  mills. The larvae eat holes in sifting silks and may also reach the mill's finished products.