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.