Division of Entomology, Indian Agricultural Research Institute, New Delhi-110 012 (India).
Amongst the seventeen sorghum resistant cultlvars, only flve, viz, P 921, P 930, P 933, P 934, P 936 were free from stem tunnelling due to borer, Chilo partellus (Swinhoe) during two years of investigation. There was no dead-heart formation in these cultlvars as well. The leaf injury grade varied from 1.0 to 4.3. On the other hand, in the susceptible checks, viz., S-40 and CSH-1, the per cent dead-heart, leaf injury grade and per cent step tunnelling varied from 22.3 to 28.2, 5.6 to 7.0, and 28.6 to 37.4 respectively. The morphological characteristics of leaf of these cultivars revealed that the presence of ligular hairs, hairy carpet base, erect hairs, tightness of leaf sheath enveloping the stem and forming acute angle, prevented the larval estabiishment. Such a situation did not exist in the susceptible cultivars as the hairy carpet base and ligular hairs were not markedly pronounced. Also, the relative tightness of the mid-rib in resistant cultivars, perhaps, provide a check in bee larval movement in the entire length of mid-ribas was evident in resistant cultivar P 921. This suggests that the leaf morphological characteristics, perhaps, govern the shift in the larval behaviour in manifesting three damage parameters ib resistant cultivars.
