Trogoderma granarium, The Khapra beetle

(Coleoptera: Dermestidae)

Host: Serious pest of stored wheat, groundnut and other grains, such as maize, rice, oat, jowar and occasionally pulses.

Damage: Both adult and larva cause damage to the grains by chewing a hole and eating up kernel. Larvae also leave cast skin in the grains, reducing their marketability.

Life Cycle: This is one of the hardiest of stored grain pests. Adult is a small sluggish beetle, 2.0-4.0 mm long, oval in shape, dark brown in colour with still darker patches on body and covered with short scattered hairs. Head is small bearing sharp, mandibulate mouth parts and short, capitate antennae. Male is smaller than female. Both sexes are slow crawlers and cannot fly, mate soon after emergence and female commences egg laying 5-6 days after mating. Adult longevity is about one month and female can lay 100-125 eggs during its lifetime.

Eggs are dull whitish, oval, 0.7 mm long, laid among the grains or stuck on the grains or laid on the container and crevices. Incubation period is about 6 days under favourable conditions.

Larvae are straw coloured, 4.5 mm long, densely covered with tufts of hairs and having long tufts of hairs on the posterior end. Larvae move freely among the grains and prefer broken grains or wheat flour and leave hairy cast skins behind. In unfavourable conditions they hide in cracks and crevices and enter diapause, a condition in which they may survive up to 4 years and recommence development when conditions become favourable again.

Larvae have 5 instars, which may take as long as 50 days in variable conditions. Pupation takes place inside the cast skin of the last larval instar. Pupa is dark brown in colour and oval in shape, male pupa being 3.0 mm and female pupa 4.5 mm long. Pupal period may vary between 6 and 15 days depending upon temperature. Under optimum humid conditions, the entire life cycle can be completed within a month.

­­Distribution: Cosmopolitan in the Old World but has not so far established in America. In India it is very serious pest in the north-western region.