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330 v. P. S. Pan wargenerally released in the evening, or earlier if the day is cloudy. In Kenya. the infestation by SSB isrecommended at 2 weeks (Kumar and Asino. 1993) and 4 weeks (Ampofo. 1986) after germination ofthe plants. The testing is also being done twice i.e. at whorl stage and flowering stage (anthesis) withabout 45 and 50 larvae per plant, respectively. The artificial infestation should be regulateddepending on the level of resistance in the plant materials. If the resistance levels are low, expressionof existing genes for resistance may be masked by heavy infestation and all genotypes may appearequally susceptible. As resistance genes are accumulated in subsequent generations infestation levelcan be increased.5. Evaluation f plaut reaction to borer damage:The reaction of plants exposed to insect attack must be measured either by visual observation oractual measurement at the proper stage of the growth. The rating scale to measure differences inresistance should be practical. rapid and reliable. To evaluate large number of germplasms. singleparameter like leaf feeding damage for visual rating scales are being practiced by majority ofresearchers. However, the studies on other parameters like stem tunnelling, exit holes etc. can betaken up to confirm resistance to maize genotypes against SSB at later stage. Kumar (1997b) reportedhighly significant correlation between number of holes and stem tunnelling and suggested that thenumber of holes can be used in place of splitting stalks for determining resistance to SSB. The leafinjury rating scale 1 - 9 (Table I) Sarup et al., (l978b) in Indian subcontinent and 0 - 9 (Table 2)Ampofo and Saxena (1987) in African countries are being followed. The foliar damage is generallyrated at 3 - 4 weeks after infestation when leaves are fully extended prior to tassel and silkemergence. Escapes occur under natural conditions and some escapes in artificial conditions also butif the proportion of escapes is not great, they can be eliminated in successive cycles of evaluation andselection. However. plants rating 0 and 1 (apparently healthy plants - likely escapes) Should not beconsidered for breeding for borer resistance. Lines or plants showing rating below 5 should beselected or pollinated for further testing.Table 1.Scale for scoring SSB damage to whorl-stage maize plants in Indian subcontinent.Visual rating DescriptionApparently healthy plant.2 Plant showing slightest damage on leaf or few pin holes on 1-2 leaves.3 Plant showing more pin holes or shot holes on 3-4 leaves.4 Plants showing injury (pin-holes, shot holes, slits) in about one- third oftotal number of leaves and mid-rib tunnellJing on 1-2 leaves, if any.5 Plants showing 50 per cent of leaf damage (pin-holes, shot holes. slits,streaks) and mid-rib damage. if any.6 Plants showing varied types of leaf injury in about two-third of the totalnumber of leaves.7 Plants with every type of leaf injury and almost all the leaves damaged.8 The entire plant showing maximum leaf injury and likely to form deadheart(such plants usually show stunted growth).9 Dead-heart.(Source Sarup et al., 1978 b)