Ovipositional nonpreference and larval development of stalk-borer, Chilo partellus Swin., on leaf-whorl and stem of 70 sorghums comprising of released varieties and hybrids, experimental high-yielding varieties, lines selected for stalk-borer resistance and local cultivars were studied in the laboratory. Data on oviposition of egg-masses as well as on number of eggs, larval duration, larval mortality and pupal weight on leaf-whorl and stem of individual variety were separately recorded. These characters were also correlated with number of holes, number of tunnels and per cent tunnelling observed in the field.
The egg-masses per seedling ranged from 0.32 to 2.25, while eggs per seedling varied from 2.25 to 20.80 on different varieties. These were highly correlated (0.92**) characters. The varieties SPV nos 35, 101, 110, 232, 257, 289, 291, 309 and 311, E 302, E 701, CSV nos 3, 6 and 8R and Aispuri were relatively less preferred for oviposition. Larval development took 17–32 days on leaf-whorl and 33–62 days on stem of the various varieties. The larval duration on leaf-whorl as well as on stem were more than average on SPV nos 35, 103, 107, 110 and 310, E 302, E 701, CSV-8R, IS 2312 and Aispuri. The larval mortality ranged from 1.7 to 95.0% on leaf-whorl and 13 to 95% on stem. Significantly higher larval mortality on leaf-whorl of SPV nos 35, 101, 292 and 311, E 302, CSV nos 3, 6 and 8R was recorded. It was 11.5 and 29.6% higher on SPV-35 and CSV-8R respectively than the most resistant variety, IS 2312. Larval mortality on leaf-whorl of early maturing varieties was 8.1% more than late varieties. The mean pupal weight was 65.55 ± 3.82 mg on leaf-whorl and 51.65 ± 4.93 mg on stem. The pupal weights were 47–75 mg on leaf-whorl and 33.5–47.7 mg on stem of local varieties.
Larval duration was positively correlated with larval mortality on both leaf-whorl and stem and negatively with pupal weight on leaf-whorl. Larval duration and mortality on leaf-whorl were negatively correlated with per cent ‘dead hearts’, and number of tunnels per plant. Larval duration and mortality on stem were also negatively and significantly correlated with holes per peduncle and per cent tunnelling. The magnitude of correlations of larval duration and mortality with tunnelling parameters were higher than that of oviposition. Though ovipositional nonpreference and antibiosis act together to determine the degree of resistance, antibiosis has a greater effect on Chilo resistance than the effect of ovipositional nonpreference.
The antibiosis factor(s) affecting larval development exists in leaf or in stem or in both the plant parts. Short peduncle varieties were less preferred for oviposition.
