Geographic Variation in Larval Survival and Growth of Six Chilo suppressalis (Lepidoptera: Pyralidae) Strains on Different Rice Hosts

Six strains of Chilo suppressalis (Walker) were collected from rice, Oryza sativa L ., farms in the Philippines. One strain originated from each of four distinct locations, and two strains originated from a fifth location. Survival and growth of these strains were measured simultaneously on the following hosts: three wild species of rice, Oryza nivara (Sharma et Shastry), O. barthii (Chev.), and O. officinalis (Wall ex Watt); three modern high-yielding O. sativa rice cultivars (‘IR40’, ‘IR56’, and ‘IR62’); and three traditional cultivars of O. sativa (‘CO18’, ‘W1253’, and ‘Rexoro’). Survival and weight gain of all stem borer strains were influenced by the specific rice host, with O. officinalis plants resulting in the lowest larval survival and weight. Survival was also low on ‘Rexoro’, but the surviving larvae did not have low weights. There were significant differences among strains in survival over all rice hosts, but strains did not differ in mean weight of 18-d-old larvae. There was no host-by-strain interaction effect for survival or weight, so there is no evidence that the six insect strains were differentially adapted to specific rice hosts.