Abstract

Studies were made on the biology, ecology and possible control of the teak trunk borer Cossus cadambae (Lep., Cossidae). Its life cycle was annual and took about 249 days for completion. The duration of the various life history stages were as follows:egg-20 days; larva-213 days; pupa-11 days; adult-5 days. The generations were continuous and overlappling. There were two peak periods of moth emergence, May and October. The distribution of this insect in the various teak plantations in Kerala was studied and the infestation was found to be more prevalent in the Central and Northern Forest Circles. Although the proportion of infested trees in the affected plantations was high, the average proportion of infestation at the Divisional level was found to be very low. Among the factors leading to infestation, mechanical injury to trees such as lopping of branches, extraction of leaves, etc. were considered important. Plantations found affected were above 20 years old and the infestation intensity was found to increase with age. It was also noted to attack Grewia tilliaefolia and Terminalia bellerica growing naturally in the affected teak plantations. The progression of attack in plantations of varying levels of infestation intensity was studied. During the initial stages of infestation the affected trees showed only minimum damage. As the infestation progressed, the damage became more pronounced due to reinfestation of the already affected trees. During these two phases the affected trees occurred in distinct patches. In the advanced, phase when the attack was heavy, the infestation became uniformly distributed in the plantation due to the initially affected patches becoming confluent with the increase in the number of affected trees. The natural enemies of this insect consist of 2 species of birds viz. the golden backed woodpecker (Dinopium benghalense) and an unidentified barbet, both predatory on the larvae, besides 6 species of microbial pathogens affecting various stages. In the pathogenicity trials maximum larval mortality was observed in the case of treatment with the bacterium, Serratia marcescens (83.3) followed by the fungi Aspergillus flavus and paecilomyces fumosoroseus (57). Control trials using the insecticides Dimethoate, Monocrotophosand Phosphamidon by trunk injection and O.S - Dimethyl Acetylphosphoramidothioate by implantion were not successful. Until suitable control measures are developed, a management strategy involving stage by stage elimination of the affected trees is suggested. This involves clearfelling of all the badly affected plantations, selective extraction of all the affected trees from plantations of low level attack during routine silvicultural thinnings and protecting the trees from mechanical injuries