PLANTÐINSECT INTERACTION Feeding Patterns of Scirpophaga incertulas (Lepidoptera: Crambidae) on Wild and Cultivated Rice During the Booting Stage YOLANDA H. CHEN 1 AND ANGELITA ROMENA International Rice Research Institute, Entomology and Plant Pathology, DAPO Box 7777, Metro Manila, The Philippines Environ. Entomol. 35(4): 1094Ð1102 (2006) ABSTRACT Rice plants are vulnerable to the yellow stem borer, Scirpophaga incertulas (Walker), during the booting phase, when infestations cause the greatest yield loss. Although the moth is ubiquitous in rice-growing regions, S. incertulas feeding patterns on booting plants have been poorly characterized. We studied the early-instar feeding patterns of S. incertulas on wild and cultivated rice accessions to determine where larvae feed and if feeding route inßuences larval survival and devel- opment. Three cultivated (Taichung Native 1, IR64, and IR72) and three wild rice accessions (two accessions of Oryza nivara and one accession of O. rufipogon) were chosen for the study. Larvae were introduced onto booting plants and sampled after 6 h, 1 d, 2 d, 4 d, and 7 d. Approximately 25% more larvae survived on cultivated accessions than on wild accessions. Larvae were also 15% more likely to feed on the panicle of cultivated accessions than wild accessions, and panicle-feeding improved larval survival and development. Stem borer feeding route depended on plant phenology; larvae were more likely to feed on the panicle than on vegetative structures on booting, heading, and ßowering tillers. Because all stems were cut by the seventh day if larvae fed on the panicle, resistance during the booting phase may be effective if it reduces the likelihood of panicle feeding or if strong antibiotic resistance can be found in the panicle. KEY WORDS domestication, host plant resistance, larval feeding behavior, Oryza, rice The yellow stem borer, Scirpophaga incertulas (Walker) (Lepidoptera: Crambidae), is an important pest of rice, Oryza sativa L., throughout tropical South and Southeast Asia (Khan et al. 1991). It is the most abundant stem borer in tropical lowland rice and deepwater rice (Catling and Islam 1995, Shepard et al. 1995) and is a damaging pest because it attacks all stages of the rice crop (Bandong and Litsinger 2005). While yield loss to S. incertulas is typically 5Ð10% (Elazegui et al. 1993, Pathak and Khan 1994, Islam and Karim 1997), it can be as high as 20% in certain regions and on particular varieties (Catling et al. 1987, Islam 1990). Larval damage to tillers during the vegetative stage results in “deadhearts,” whereas damage during the booting stage results in “whiteheads” or unÞlled panicle grains. The boring behavior of the larvae limits the range of management options. Chemical foliar sprays are only effective before the larvae enter the plant, whereas systemic insecticides are not com- pletely effective or are too labor intensive to use (dela Cruz et al. 1981, Reissig et al. 1986, Khan et al. 1991). Although egg parasitoids strongly impact S. incertulas (Catling et al. 1983, Kim et al. 1986, Shepard and Arida 1986), larval and pupal parasitoids do not seem to be a signiÞcant cause of mortality (Chandramohan and Chelliah 1984, Khan et al. 1991). Predators are also important natural enemies in controlling stem borer populations (Ooi and Shepard 1994); however, S. in- certulas can still cause signiÞcant yield losses, espe- cially if combined with other biotic and abiotic stresses (Khan et al. 1991, Litsinger 1991, Savary et al. 1994). As a consequence, control efforts have focused on breeding resistant rice varieties (Chaudhary et al. 1984, Heinrichs et al. 1985, Khan et al. 1991). There has been moderate success in controlling moth populations in the Þeld; varieties with moderate levels of resistance have been credited as an important source of control against S. incertulas (Heinrichs 1988, Way and Heong 1994). Many rice varieties are avail- able with moderate levels of resistance to S. incertulas during the vegetative stage (Chaudhary et al. 1984, Heinrichs 1988). SigniÞcant mortality occurs when larvae attempt to tunnel into the plant during the vegetative stage. Islam (1994) found that 96% of Þrst- instar larvae died after boring into a resistant rice plant, whereas, of those successfully penetrating the stems, 39% of larvae died before pupation. Resistance during the vegetative stage has been associated with higher silica content, which reduces larval develop- ment by physically wearing down the mandibles (Djamin and Pathak 1967, Subbarao and Perraju 1976). Chemical resistance has also been documented in the leaves (Ishii et al. 1962); benzoic acid, salicylic acid, and fatty acids isolated from resistant plants slow 1 Corresponding author, e-mail: y.chen@cgiar.org. 0046-225X/06/1094Ð1102$04.00/0  2006 Entomological Society of America