Flotation technique for quantitative determination of mite populations in powdered and compacted foodstuffs

Samples are preheated in 25% aqueous ethanol at 65 degrees C for 5 min. A specially designed flotation flask and solvent mixture of kerosene-tetralin (1+1) is used to form an interface with 25% aqueous ethanol. Mites, insects, and insect fragments are separated from vegetative material by an overflow method. Trials incorporating a known number of mites in samples of pigmeal indicate that at an infestation level of 1000 mites/kg the method always recovered 70% of the population and at 2000 mites/kg, 75%. The method permits collection of mite specimens for microscopic examination as well as allowing differentiation between live and long-dead insects. It does not use highly volatile solvents or corrosive acids. The apparatus has been successfully tested for quantitatively determining mite populations in flour, dried skimmed milk, animal feedstuffs, soya meal, wheat, rape seed, dates, and house dust. It has also been used to estimate insect contamination in packaged dates.