Inßuence of morphology of leaf sheath of sugarcane and Erianthus for infestations of internode borer (Chilo sacchariphagus indicus, lepidoptera: Crambidae) in Sri Lanka

The sugarcane internode borer (INB) (Chilo sacchariphagus indicus) is a major pest affecting sugarcane in Sri Lanka. Plant resistance is a key strategy for controlling this pest. This study investigated the relationship between INB infestation and two leaf sheath morphological traits (leaf sheath thickness and leaf insertion hairs/LI hairs) in 21 Erianthus accessions and five sugarcane cultivars. INB infestations were recorded from the field trial at Udawalawe (6⁰ 27’N, 80⁰52’E), Sri Lanka in three-month-old plants. The thickness of leaf sheaths was measured using cross-sections, and the length and weight of LI hairs were quantified to determine their density. Additionally, the effect of LI hairs on neonate larvae of INB was studied by measuring the time taken by larvae to pass through the LI hairs of each variety. Results showed that IND 8180 had the highest infestation (13.5±0.4^a), while MOL 4503,Co 775, and SL 83 06 had no infestations. Significant differences were observed in leaf sheath thickness, with Co 775 showing the highest thickness (847.2±2.1^a), followed by SL 83 06 (728.8±2.9^b). A strong negative correlation (r = -0.6) was found between leaf sheath thickness and INB infestation. LI hairs were present only in Erianthus accessions, with the longest hairs found in IK 76 62 and IK 76 73 (3.5±0.2^a and 3.5±0.3^a) respectively. A negative correlation between hair weight and infestation (r = -0.5) was also observed. Larvae took the longest time to pass through the LI hairs of MOL 4503 (28.32±0.31^a). The study highlights the importance of leaf sheath thickness and LI hair density in developing pest-resistant cultivars against INB.