Stored Grain Insects



Warehouse beetle

Trogoderma variabile



Larvae of warehouse beetle (Trogoderma variabile)
? Agriculture Western Australia

The larvae of the warehouse beetle (Trogoderma variabile) are white-brown in colour, about 6 - 8 mm long and conspicuously hairy. The adults are dark brown in appearance with mottled lighter brown markings. They are about 1.5 - 4 mm in length, have an oval shaped body and occasionally fly.


Warehouse beetle (Trogoderma variabile)
? Agriculture Western Australia

Life cycle
Eggs are laid singly and are deposited loosely in processed commodity or in the crevices of whole kernels. The eggs hatch after about 6 days and there are normally 6 larval instars. If a larva does not diapause, it requires approximately 34 days to pupate. Diapause is a period of dormancy and can last up to two years. Molting can continue at irregular intervals. The percentage that diapause increase from 32 to 67 when exposed to room temperature daily and this increases to 80% when handled daily along with room temperature storage. Generally, larvae that take more than 7 weeks to complete development are probably in 'diapause'. Pupation lasts 5 days and males generally pupate after 1 less molt than females. Pupation generally occurs near the surface of the food. The females usually begin laying eggs one day after emerging and continue to do so for 3 days. The adults live between 1 - 5 weeks.

Larval skins associated with infestation
? Agriculture Western Australia

Warehouse beetles are voracious feeders. They have been reported from seeds of all kinds, dead insects and animals, cereal products, candy cocoa, corn, corn meal, dog food, fish meal, flour, oatmeal, milk powder, spaghetti, spices, peas, wheat, barley, and pollen. In grain they cannot feed on whole grain, but can feed on broken kernels that are usually present. A notable feature of warehouse beetle infestations is the accumulation of skins shed by the larvae, which may moult up to ten times before pupation. Hairs shed by larvae may cause asthma, skin or gastric problems.

Warehouse beetle
Courtesy of CSIRO Division of Entomology

Warehouse beetle thrives where it is undisturbed, so the basic requirement for control is regular thorough cleaning of premises to remove potential host material.