Grain Beetles
(Red flour beetle, Confused flour beetle, Rusty grain beetle)*Tribolium castaneum* / *Cryptolestes ferrugineus*
Identification & Appearance
Grain beetles are secondary stored-product pests feeding on broken kernels, flour, and grain debris. The sawtoothed grain beetle (2.5-3.5mm) has six sawtooth-like projections on each side of the pronotum. Their flattened bodies enable hiding in packaging folds and cardboard. At 25-30 C, the cycle takes 4-8 weeks.
Habits & Hiding Places
Grain beetles feed on broken grain, flour, bran, and mold. They concentrate in flour accumulations, cardboard boxes, and wood crate crevices. Flattened bodies allow entry into the narrowest gaps. Cold kills all stages. Dispersal is mainly by crawling.
Health Risks & Damage
- Infested flour cakes, discolors, and develops off-odors.;
- Body fragments and frass mix into flour, hard to detect visually.;
- Once in cardboard or wood crevices, nearly impossible to get rid of by normal cleaning.;
- Their presence signals primary pest problems creating grain damage they feed on.
Season & Region
Cosmopolitan. Optimal developmental temperature 27–30 °C, RH 70 %. 4–6 generations per year; adults overwinter in packaging and warehouse crevices. At 30 °C a complete generation takes only 27 days. Thigmotactic (seeking confined spaces); gregarious; secrete odorous defensive quinones.
| Region | Active Period | Peak Season | Notes |
|---|---|---|---|
| N. Hemisphere Temperate | Apr–Oct | Jul–Sep | Summer hot-humid reproduction peak; adults overwinter |