Abstract

The impact of insect-caused defoliation on plantation-grown teak [Tectona grandis] was studied at Nilambur in Kerala, India. Experimental plots in a 4-year old plantation were either given selective protection against one or both of the two dominantdefoliators (Hyblaea puera and Eutectona machaeralis) or left unprotected for about 5 years. Measurements made on trees felled during the first and second mechanical thinning were used to establish prediction equations for volume, based on girth at breast height (gbh) and height, using which the volumes of the experimental trees at the beginning and end of the experimental period were determined. The increments were compared using statistical methods involving analysis of covariance in which the initialvalue of the dependent variable and the number of neighbours of each tree were used as covariates. E. machaeralis which feeds on older leaves towards the end of the growth season had no significant impact on tree growth. H. puera which