Sieving Infested Flour: The Aperture That Removes the Adults and Leaves the Eggs, and the Finer Mesh That Still Leaves Most of Them

Sieving is the traditional household response to flour beetles, performed with whatever sieve the kitchen holds. This study computes stage-by-stage removal for the red flour beetle using stated stage widths (egg 0.35 mm, young larva 0.5 mm, older larva 0.9 mm, pupa 1.1 mm, adult 1.2 mm), a logistic retention curve, and a starting contamination of 98 insects per kg across stages. A common 1.0 mm kitchen sieve removes 94.3 percent of adults but only 17.2 percent of all stages, and effectively no eggs. A 0.6 mm mesh removes 39.6 percent overall; 0.45 mm removes 58.8 percent, including 19.8 percent of eggs, at a stated flour handling loss of 4.5 percent; even 0.3 mm removes only 85.0 percent overall and 66.8 percent of eggs. Sieving therefore cannot clean infested flour — it can only decapitate the visible population — and the originated rule is to sieve for inspection and salvage decisions, never as a cure: flour worth keeping should be frozen or heat-treated after sieving, and flour with contamination near the modelled level should be discarded. This study is simulated, not measured. SIMULATED, NOT MEASURED.