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Rust Red Flour Beetle

Tribolium castaneum


The adults are 2.3-4.4 mm in length and are reddish-brown in colour. The antennae are distinct with a 3 segmented club at the tip.


Flour beetles are generally recognised as secondary pests of grain and therefore increase the feeding damage done by primary pests. When present in large numbers, flour beetles will:

  • Cause flour to become prone to moulding and will also turn the product grey

  • Taint commodities with secretions from scent glands


Up to 450 eggs are laid singly at a rate of 2-10 per day, depending on temperature. The white eggs are sticky and rapidly become coated with food particles and other debris. At 22-27 °C they hatch in 6-14 days. The larvae are white tinged with yellow and pass through 5-11 moults before reaching a full-grown length of 5 mm. This process takes 3-9 weeks. Pupae lie in the same foodstuff as the larvae. They are initially white, but gradually darken in colour prior to adult emergence after 9-17 days. Adults feed on the same food as the larvae and live for 15-20 months. There may be five generations per year.


The rust-red flour beetle can infest stored cereals and oilseeds but is more of a serious problem in cereal products such as flour and animal feedingstuffs. Other products which may be attacked are oil cake, nuts, dried fruit, spices, chocolate - even bones and other animal products. The beetles are not cold hardy, so they will only overwinter under warm conditions. They are active insects which will seek cover if disturbed and, because they are so small, can exploit the smallest crevice. They are a particular problem in machinery where cereal and other food residues accumulate.

Management of storage pests

  • Use trapping methods to identify and measure insect infestations

  • Clean stores thoroughly before harvest and seal all building cracks and crevices

  • Store grain at <15 % MC and <15 °C

  • Where appropriate apply insecticides to the fabric of stores or apply grain protectants

Rust-red flour beetle, Tribolium castaneum

confused flour beetle adults, Tribolium confusum