Rust-red flour beetle (Tribolium castaneum)

Red flour beetle is considered to be a major pest of shelled groundnuts. It is found throughout the tropics. The female lays about 450 eggs at random in the produce. The cylindrical larvae that hatch out of these eggs feed on the kernels. Pupation takes place inside the nuts without a cocoon. The adult beetles which damage the kernel, survive for about eighteen months. The developmental period – from egg to adult – is about twenty days. Red flour beetle has been found to cause 4.5% losses in weight and 73% losses in germination. As a result of the damage, free fatty acid content of the groundnut oil increases, resulting in deterioration of its quality.

Adult beetles are about 2.5 mm long and brownish; the thorax bears six saw-tooth-like projections on each side. The whitish larva has a brown head, which is small, slender and slightly longer than the adult. Each female is capable of laying 300 eggs loosely on groundnuts. Both adults and larvae feed on the produce and the adults may live for up to three years.

This pest is common throughout the tropics but is less prevalent in arid areas. It commonly infests stored shelled groundnut. It is a dull greyish brown moth. The forewings have obscure markings, with an outer pale band and broad dark band with a broad pale band on the inner edge. The adult avoids strong light and rests in dark places during daylight. The female lays up to 300 eggs in the groundnut produce often by simply dropping the eggs through holes between the fibres in jute bags or by laying eggs liberally on the surface of the kernels. The larvae move freely through the produce contaminating it with webbing and frass. They feed on the kernels until they are mature. In optimum conditions at 28 °C and 70 percent RH, the eggs hatch in three days, develop from egg to adult in about 24 days and complete their life cycle within 40 to 50 days.

This species of moth has the ability to develop at low humidity (<20 percent RH). The adult is brown and 12 to 15 mm long with its wing folded. The head bears a projecting tuft of scales. The female lays up to 150 eggs within a few days of emergence from the cocoon. The larvae feed upon and within the kernels. Infestation causes aggregation of kernels by the presence of webbing. The development period at optimum temperature is four to five weeks. The larvae are capable of damaging intact kernels and can feed both on the surface and within the seed. They spin a tough silky fibre, webbing together kernels and frass and cast larval skins.

This species is cosmopolitan in distribution. The adults are 2.5 to 3.5 mm long with a distinctive ridged prothorax bearing six large teeth on either side. Each female lays about 300 eggs loosely in the groundnut over a 10-week period. The eggs hatch into cream coloured larvae, which move freely until fully grown. Both adult and larvae feed on the produce and the adult may live for as long as three years. The life cycle is completed in four to five weeks under optimum conditions at 30 °C and 70 percent RH. The adult and larva burrow into the groundnut seed causing 'warm-cut' groundnut and an increased percentage of split seed. Losses occur through contamination of the product by live and dead insects, cast skins and excrement.

This species is found in India, Gambia, Senegal, and West Africa. It breeds on common trees such as Tamarindus indica L. and harvested groundnuts. It can penetrate intact pods to infest the kernels. Infestation of the harvested groundnuts can occur while the crop is being dried in the field, stored near infested stocks or crop residues. Adult females attach their eggs to the outside of pods or kernels. When the first instar larva hatches, it burrows directly through the pod wall to reach the kernel, where the larva feed and develop. A single larva can make a large excavation in the cotyledons, but no sign of damage is visible externally at this stage. Mature larvae emerge partially or completely from the pod and construct an oval papery cocoon. The egg to adult development period is about 42 days. The adult is 4 to 7 mm long, with small black markings on the elytra. It is readily distinguished from the other pests of groundnuts by its very broad hind femur, serrate antennae and elytra that do not completely cover the abdomen.

This bug is widespread in tropical Africa and India, occurring on pods left for drying in the field and in storage. The adult is dark brown, approximately 2 mm wide. In the field females lay their eggs in the soil or on groundnut haulms. In storage, eggs are laid loosely among the groundnuts or in the sacking. The first instar nymphs have a bright red abdomen; later instars become progressively darker. All stages feed on kernels, perforating the pods with their rostrum. This causes the kernels to shrivel and increases the free fatty acid content of the oil, producing a rancid flavour.

This species is more frequently found in cooler areas of the tropics. The basal third of the forewing of this moth is a pale yellowish buff colour. The remainder is reddish brown. The larvae feed on and within kernels and spin a silken thread on which the larval droppings accumulate. Females lay about 500 eggs at a time. Development from egg to adult takes about 26 days. The life cycle of this moth may be prolonged by diapause under certain temperature conditions. During diapause the metabolic activities are very low and normal application rates of control chemicals, especially use of fumigation, may not prove effective.

These species (Alphitobius diaperinus and A. laevigatus) are 5 to 7 mm long. They feed upon damp kernels, groundnut cake and other grain residues. Their presence in groundnut storage and oil extraction mills is indicative of poor storage conditions involving spillage and dampness.

• Groundnut must be dried properly after harvest to reduce the moisture content of the kernels to 7% for safe storage. At high moisture levels, insect populations develop more rapidly and there is an increased risk of invasion by toxic fungi, with a consequent danger of aflatoxin contamination.
  
• The stacks should be piled on wooden pallets to reduce the possibility of ground water seeping into the bottom sacks.
• Plant materials such as crushed neem seed, neem leaves or neem oil, which have antifeedant or repellant effects on storage pests, can be used.
• Storage godowns should be kept clean. All the waste and unwanted materials in the godown should be periodically removed.
• The gunny bags should be stacked with proper aeration.
• The gunny bags bought for seed storage should be treated with 10% neem kernel extract before they are used. The neem kernel should be used immediately after preparation. The gunny bags should be soaked in the extract for 15 minutes. The gunny bags should be shade dried and used for storing grains. In case the gunny bags are new they should be soaked for half an hour. If the gunny bags are with a close mesh and small pores, a thinner solution should be prepared. By this method, the grains can be protected from insects for about four months.
  • Storage godowns or rooms should have proper ventilation and aeration.