Lethal and sublethal effects of rice polishing process on Sitophilus oryzae (Coleoptera : Curculionidae)

The mechanical impact of rice polishing on the rice weevil, Sitophilus oryz ae (L.), and the subsequent postpolishing effects associated with rice qual ity were studied. "Brown" rice (not polished),"White (infest then polish)" rice, and "White (polish then infest)" rice were used with different polish ing process intensities and different initial weevil densities. Weevil prog eny were more numerous in Brown than in White (infest then polish) or White (polish then infest) rice. Polishing corresponding to a weight loss of 11% in rice generated an immediate mortality of approximate to 40%; the subseq uent mortality caused by rice quality was also 40% (total >80%). A polishin g process corresponding to 14 and 16% of rice weight loss generated a drast ic mortality in the weevil population (>95%). The progeny per adult weevil was similar with high and low initial weevil densities. The development of weevil progeny was also delayed by about 1 wk in White (infest then polish) rice compared with Brown rice. Furthermore, weevil adults of the progeny w ere significantly heavier in Brown than in White (infest then polish) or Wh ite (polish then infest) rice.