Oviposition preference of rice weevil Sitophilus zeamais Motschulsky (Coleoptera: Curculionidae) , for unpolished and polished rice
Arakaki, N.; Takahashi, F.
Japanese Journal of Applied Entomology and Zoology 263: 166-171
The oviposition preference of the rice weevil for unpolished, polished, parboiled-unpolished and parboiled-polished rice was evaluated, and the factors causing 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 embyronic part. When the grain was ground into powder, weevils did not deposit the eggs in the rice flour, while they did 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. The aleurone layer and the embryo, which are coated by the pericarp, probably contain 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.