Abstract

The seasonal incidence of defoliation and its effect on the growth of teak [Tectona grandis] were studied in plantations in Kerala, India, in 1978-1982. Experimental plots in a 4-year-old plantation were either treated with insecticide or left unprotected for 5 years. The hyblaeid Hyblaea puera and the pyralid Eutectona machaeralis were the dominant defoliators. Defoliation by H. puera was a regular annual feature, with 1 or 2 waves of epidemic defoliation between late April and July followed in some years by another lighter defoliation between late August and October. In contrast, defoliation by E. machaeralis was generally more infrequent, of a low intensity and later in the season. A model of the population dynamics of H. puera is proposed. The most serious impact of defoliation was loss of volume increment. E. machaeralis had no significant impact on increment, but H. puera caused a loss of 44 of the potential increment in volume during the experimental period. When the gain due to protectionwas expressed as percentage increase over the normally realized unprotected yield it amounted to 80