Primary pests Primary pests attack and breed in previously undamaged cereal grains and pulses. They also feed on other solid but non-granular commodities, but they are rarely successful on milled or ground foodstuffs. Primary pests are usually more destructive than secondary pests, especially in short-term storage.  Sitophilus spp. beetles are important primary pests of whole cereal grains and are called weevils. Three species are pests of stored grain: Sitophilus zeamais (maize weevil), Sitophilus oryzae (rice weevil) and Sitophilus granarius (granary weevil). The common names are misleading because they suggest the pest is restricted to particular grains, which is not the case. - Color: body colour ranges from light to dark brown, and both S. zeamais and S. oryzae often have four large, reddish-orange spots on their wing cases
- Size: 2.5 - 4.5 mm long / adult life-size
- Cycle (under favorable conditions, i.e 27 °C and fairly high humidity): about 35 days
Sitophilus zeamais (adult life-size, 2.5–4.5 mm long) showing its life cycle in a wheat grain; note female laying egg in hole in the grain. Sitotroga cerealella is an important primary pest of cereals. - Color: forewings of newly emerged adults are yellowish-golden, but older adults body is grey.
- Size: wingspan 10-18 mm
- Life span: adults 7-10 days
In the photo, the Sitotroga cerelella adult, pupa, larva and grain with emergence window.
Species of Callosobruchus are important primary pests of a number of legumes including cowpeas, pigeonpeas, chickpeas, adzuki beans, peas, grams and (occasionally) soyabeans. They do not usually attack kidney beans or butter beans (Phaseolus spp.) - Size: Callosobruchus chinensis - life-size, 2.0-3.5 mm long,
| Secondary prests Secondary pests are able to attack only materials that have been previously damaged either by other pests (primary pests) or by poor threshing, drying and handling. They also attack processed commodities such as flour and milled rice, where they may form the majority of insects present. Trogoderma granarium is a very serious pest of cereal grains and oilseeds, and many countries have specific quarantine regulations against possible importation. The presence of T. granarium on grain exported to some countries will result in an order to carry out expensive pest control measures or a rejection of the shipment. - Size: adults 2.0–3.0 mm long.
- Color and aspect: wings mid-brown or irregularly mottled. The larvae are extremely hairy. Hairs from the skins are allergenic, presenting a health hazard to storage workers and consumers.
- Growth conditions: high temperature and low humidity.
Tribolium castaneum feeds on a range of commodities, especially cereals, but also groundnuts, nuts, and occasionally pulses. - Color: brown
- Size: 2.5–4.5 mm long
- Growth conditions: optimum conditions (33–35 °C at fairly high humidity) adults live for many months
- Life cycle: about 30 days
- Heavy infestation: can produce disagreeable odours and flavours in commodities due to the production of quinones.
Several species of Cryptolestes are common in mills and stores where they are secondary pests of cereals, nuts, oilcakes, dried fruit and other commodities. - Size: 2.0–2.5 mm lon.
- Color: light-coloure.
- Growth conditions: in food with high moisture content.
Oryzaephilus surinamensis is a cosmopolitan secondary pest of cereals, mainly milled products such as flour, meals, breakfast foods, stock and poultry feeds, copra, confectionery and dried fruits. After a preoviposition period of 54 days the female lays some 375 eggs (at 30°C) over a life-span of 6-8 months but may be prolonged at low temperatures. - Colour: brown beetle with serrated lateral margins of thorax.
- Size: 2.5–3.5 mm long
- Growth conditions: development rapidly within 22 days at 30°C and 68 days at 20°C (at 70% R.H.). The species is very tolerant of low humidities and even at 30°C and 10% R.H.The life-cycle can be completed over 20°C to 37.5°C, the optimum range being 31-34°C.
Lasioderma serricorne, known as the tobacco beetle, is also important secondary pest of cereals and grain legumes. The complete life cycle takes 26 days at 37 °C and 120 days at 20 °C. L. serricorne cannot tolerate the cold, adults die within 6 days at 4 °C, and eggs survive 5 days at 0–5 °C. - Color: light-brown
- Size: 2.0 - 2.5 mm long head curved under thorax
- Adult life span: 2–6 weeks.
Stegobium paniceum (drugstore beetle) is a cold-hardy cosmopolitan pest and can survive winter conditions. It infests almost any dry animal or plant products and it particularly attacks breakfast foods, biscuits, etc. The adult beetle cannot fly and its dispersal depends on passive distribution during the movement of goods. - Size: 2.0-3.5 mm, cylindrical with very long last three anthennal segments.
- Colour: light brown beetle
- Adult life-span: 40-90 days
- Optimum growht conditions: At 20-25°C and 60-80% R.H.
The life-cycle can be completed over 15-34°C, development taking 40 days at about 30°C and 60-90% R.H. At 20°C development takes about 100 days at 90% R.H. and 130 days at 60% R.H. Cadra cautella is a common and important secondary pest of cereals, cereal products, cocoa, dried fruits, nuts and many other commodities. - Color: forewings are greyish-brown with an indistinct pattern & older specimens are dull grey
- Life span: usually 7–14 days
- Heavy infestation: webbing mat the commodity together & render it unfit for consumption.
- Color: forewings, the inner parts of which are pale yellow, while the basal parts are dark reddish-brown
- Size: wingspan 11 - 28 mm
Psocids, or booklice are small insects and are often confused with mites. Psocids are not associated with significant damage or losses, and in many situations their numbers can be kept low by simple hygiene measures. The eggs of psocids are particularly tolerant of the fumigant phosphine. How to control psocids? - OPTION: Attempt a single, very good quality fumigation. This could be a 5-day treatment of phosphine (at 27 °C) in which at least 1275 ppm (1.7 mg/l) is still retained on the last day or a 8-day treatment in which not less than 38 ppm (0.05 mg/l) is retained on the last day.
- OPTION: Undertake two normal fumigations in succession. The second fumigation follows after about 10 days, when any surviving eggs will have developed into nymphs.
- Color: whitish, cream or milky translucent in colour
- Size: 0.3 - 0.8 mm
- Growth condition: upper temperature limit is 35–37 °C, optimum at 32 °C, all humidity conditions.
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