Impact of Rice Genotypes on the Developmental Characteristics of Rice Leaf Folder, Cnaphalocrocis medinalis
Rice leaf folder, Cnaphalocrocis medinalis (Guenee.) (Lepidoptera: Pyralidae) developmental characteristics were studied on different categories of rice genotypes viz., susceptible, resistant, hybrid, scented, popular and wild rice genotypes at Agricultural College & Research Institute, Madurai, Tamil Nadu during 2005–2008. Longer pre-oviposition and incubation periods; and shorter ovipositional period and lower fecundity were recorded on resistant (TKM 6, Ptb 33 and LFR 831311) and wild genotypes (Oryza minuta and O. rhizomatis). C. medinalis larvae completed instar-wise development up to fifth instar and pupal growth in a quicker manner along with higher growth index on susceptible, scented, hybrid and popular genotypes as compared to resistant and wild genotypes. Regarding sex ratio, females dominated males during emergence irrespective of the genotypes. However, longevity of males and females was slightly shorter on resistant and wild genotypes than other genotypes. Feeding on susceptible, scented, hybrid and popular genotypes resulted in increased length and breadth of C. medinalis from second to fifth instar. However, decreased length and breadth parameters were observed on wild and resistant genotypes. C. medinalis eggs, larvae and pupal survival was comparatively less on resistant and wild genotypes than susceptible and other genotypes. Therefore, our results confirmed that the mechanism of resistance against rice leaf folder is combination of antixenosis and antibiosis.