SOME FACTORS AFFECTING WHITE STEM BORER SCIRPOPHAGA-INNOTATA (WALKER)(LEPIDOPTERA, PYRALIDAE) INJURY TO RICE

The amount of injury to rice caused by white stem borer Sciryophaga in notata depends on cultivar, and stage of plant and insect development, as well as insect abundance. Of the cultivars tested, IR64, IR42, Cis adane and Ketan. IR64 were the most susceptible and Ketan the least su sceptible to feeding damage. Third and fourth instars consumed more st em dry matter than other stages, although yield reduction depended on the number of tillers injured. On the wider stemmed Ketan, fewer tille rs were injured than the narrower IR64. Larvae are more likely to move among tillers in the third instar stage, which tends to coincide with maximum tillering and may result in more tillers injured and in yield reduction. Later instar larvae burrow downwards to the internode wher e they pupate. Larvae appear to move less among tillers in 'resistant' cultivars. Management strategies should target this pest at third ins tar and when its abundance in the field warrants control. Fewer than 1 0% of the neonates establish successfully on stems, and this mortality needs to be taken into account when deciding on control, as does the ability of rice plants to compensate for injury. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.