Sugarcane Breeding Institute, Coimbatore-641 007, Tamil Nadu (India).
The role of leaf-sheaths, stem surface waxes and stem hardness in relation to the colonisation and population density of two of the important coccid pests, viz., the scale insect, Melanaspis glomerata (Green) and the mealy bug, Saccharicoccus sacchari (Ckll.) infesting the sugarcane plant was studied under pot culture conditions. The presence of a leaf-sheath was inevitable for the settlement and colonisation of S. sacchari; while for M. glomerata, the differences in the mean per cent intensity and severity were not found to differ significantly on plants with leaf-sheaths intact and those with leaf-sheaths removed. The infestation and colonisation of both these pests did not vary significantly on sugarcane genotypes with a heavy coating of surface waxes, viz., G 229 and Co 6806 and on those with negligible/moderate coating of stem waxes, suggesting that waxy stem had no influence on the infestation of coccids on the sugarcane plant. Similarly, stem hardness as a physical factor was not related to the infestation and severity of both M. glomerata and S. sacchari. The softest bud portion as well as the hardest nodal portion of the top and middle regions of the stem were equally heavily colonised by S. sacchari, though the same portions in the basal part of the stem were invariahly least colonised by this pest. The moderately hard internodal portion was always noted to be the area heavily colonised by M. glomerata as compared to the softer bud portion, indicating that mere softness of a portion was not a factor to induce/promote its colonisation.
