Spatio-temporal analysis of insect pests infesting a paddy rice storage facility

The study describes the temporal and spatial distribution of the insect fauna collected in a paddy rice storage facility over two years, with major emphasis on the most abundant pests. The experiment, using 19 food-bait traps, was carried out in the county of Massaranduba, State of Santa Catarina, Brazil, from November 1997 to October 1999. During the whole survey, Sitophilus oryzae (L.), a primary pest associated to stored cereals, was the most abundant species in the storage facility (28,542 specimens captured). Other beetles were collected in remarkable numbers, both primary pests, such as Rhyzopertha dominica (Fabricius) (3,931 specimens), and secondary pests, such as Cryptolestes ferrugineus (Stephens) (4,075 specimens) and Oryzaephilus surinamesis (L.) (1,069 specimens). In general, various species showed very variable distribution and, depending on pest and year, all parts of the facility appeared infested. Pest populations were present both in processing area and in silos, at least in one of the two years survey. Analyzing different distributions, the various zones of the rice facility appeared to have different propensity to insect infestations, with the south-eastern silos and the grain pit with the conveyor belt as the most frequently infested. Moreover, variations between the 1(st) and 2(nd) year survey showed a strong decrease of total population numbers in the 2(nd) year, but in different ways, depending on the species considered. Such a result was probably due to the cleaning measures accomplished inside and outside the silos and in the processing area, including application of insecticide on the structure.