Resistance of cultivated rice varieties to Cnaphalocrocis medinalis (Lepidoptera: Pyralidae).

Cnaphalocrocis medinalis Guenée (Lepidoptera: Pyralidae) is a major pest in rice, Oryza sativa L. (Graminales: Poaceae), in Asia. The current study investigated the resistance of 17 rice varieties or lines to C. medinalis and behavioral responses of the insect to varieties of different corrected damage ratings (CDRs) and damaged leaves scales (DLSs). The results showed that most varieties (or lines) commonly cultured in rice production were susceptible (DLS 3 and 5) to damage caused by C. medinalis; Yangjing 9538, 91SP, and TN1 were the most susceptible (DLS 7 and 9). A significant positive correlation was observed between CDR and leaf width and chlorophyll content in rice leaves, whereas no significant correlations between resistance and plant height and leaf length were found. The number of eggs laid by C. medinalis adult females significantly increased with CDR. There was a significant difference in the number of eggs laid for varieties of different DLSs. The number laid on varieties of DLS 9 was 44.4, 134.5, and 466.7% greater than DLS 7, 5 and 3, respectively; the number laid on varieties of DLS 7 was 65.5% greater than DLS 5 and 300% greater than DLS 3; and the number laid on those of DLS 5 was 141.7% greater than DLS 3. Developmental duration (day) of larvae, the body length of fifth instar larvae and pupae weight also significantly increased with CDR. A significant difference of to excised leaves was also found among different DLSs with a higher proportion of both first and third instars settled on the leaves of high DLS. Dispersal experiments of larvae on excised leaves showed that the number of first instars that remained settled gradually increased with DLSs. These findings suggested that rice of higher DLS are more suitable for feeding and settling of larvae.