Mite contamination in polished rice and beans comercialized in municipal markets

Objective To evaluate mite contamination rate in grains commercialized in n ine municipal markets of the city of Sao Paulo, in the period from November 1989 to November 1990. Methods 23 samples of polished rice and 53 samples of beans were microscopi cally examined after sieving once a week and during 42 days at air temperat ure. Other sample fractions,were kept in an incubator at 25 degrees C and 7 5% relative Humidity (RH) during 28 days Results Samples were negative for mites in the first day of analysis and we re detected after incubation. Samples incubated revealed a higher percentag e of positive examinations for mites (incidence): 31.7% (and 1,845 mites); while samples kept at air temperature showed only 6.9% (and 45 mites). Samp les of polished rice were more contaminated in comparison to the ones of be ans. There was a larger amount of mites when the mean monthly temperature o f the laboratory was between 21.5 degrees C to 22.5 degrees C (37.8%) and h umidity between 73.5% to 74.5% (31.1%). Conclusions The predominant species was Tyrophagus putrescentiae and other identified species were Blomia tropicalis, Cheyletus, spp., Blattisocius ta rsalis, and others. Mite population had a higher proliferation rate during spring, summer and in the beginning of autumn, due to highest temperature a nd humidity. These results confirm the importance of improving grains stora ge, to avoid mites proliferation.