Abstract
The oviposition preference of the rice weevil for unpolished, polished, parboiled-unpolished, and parboiled-polished rice was evaluated, and the factors causing the preference behavior were considered. The preference order was as follows: parboiled-unpolished rice>unpolished rice>parboiled-polished rice>polished rice. The degree of preference decreased with the increase of milling intensity of the rice grain. Weevils had a tendency to deposit the eggs on a particular area of the grain, especially on the embryonic part. When the grain was ground into powder, weevils did not deposit the eggs in the rice flour, while they did it on the pellets made of powdered rice. The eggs were deposited 1.7 times more often on the pellets of unpolished rice than on those of polished rice. When the methanol extract of rice bran was added to the pellets of polished rice flour, the rate of oviposition was higher than when no extract was present. It was considered that the aleurone layer and the embryo which are coated by the pericarp contained oviposition stimulating substances. Rice processing procedures, such as polishing and parboiling, affected the structure of the surface of rice grains and the distribution of substances within a grain determining the order of oviposition preference.
