Mite contamination in polished rice and beans comercialized in municipal markets

Abstract

OBJECTIVE: To evaluate mite contamination rate in grains commercialized in nine municipal markets of the city of São Paulo, in the period from November 1989 to November 1990. METHODS: 23 samples of polished rice and 53 samples of beans were microscopically examined after sieving, once a week and during 42 days at air temperature. Other sample fractions were kept in an incubator at 25°C and 75% Relative Humidity (RH) during 28 days. RESULTS: Samples were negative for mites in the first day of analysis and were detected after incubation. Samples incubated revealed a higher percentage 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). Samples of polished rice were more contaminated in comparison to the ones of beans. There was a larger amount of mites when the mean monthly temperature of the laboratory was between 21.5°C to 22.5°C (37.8%) and humidity 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 tarsalis, and others. Mite population had a higher proliferation rate during spring, summer and in the beginning of autumn, due to highest temperature and humidity. These results confirm the importance of improving grains storage, to avoid mites proliferation.