Effective control of termites in Eucalyptus spp.

Among forest species eucalypt seedling is one of the most susceptible to termites. Eucalyptus seedlings upto about 1 year old are highly susceptible to attack by termites which feed on the roots. Investigations showed that the roots contained some substance which was attractive to termites. Extracts of the roots prepared in acetone and alcohol were found active as attractants in bioassay. Chemical characterization of the eucalypt root extract showed the active substance to be a phenolic acid.

Effective control of termites is usually achieved by long persistent synthetic pesticides like aldrin, chlordane or heptachlor. The possibility of replacing these chlorinated hydrocarbons by some non-insecticidal methods of control are mentioned below:

Termites cause serious damage to agricultural crops, forest trees, stored timber and other wood products. In most cases satisfatcory control of termites can be achieved with long persistent synthetic pesticides, provided the right chemical is used at the appropriate time. Among forest plantations, Eucalyptus spp. are attacked by termites during early stages of establishment, often causing considerable mortality. Field studies have shown that usually eucalypt seedlings below one year are attacked by termites. The mortality may be as high as 80%. The point of attack in general, is the living root system. Methods of control using cyclodiene insecticides have been standardised.

Search for pest control agents of natural origin has assumed greater importance in recent years due to the increasing cost of synthetic chemical pesticides and pollution problems. In addition, there are problems of outbreak of secondary pests and toxic effect on natural enemies of pests. In view of these problems several attempts have been made to control termites using alternative methods of control. These include use of attractant wood blocks together with a slow-acting termiticide, use of repellents or termite resistant materials and application of juvenile hormone analogues which can cause disturbance to the physiological or behavioural processes in insects. Known termite attractants include several constiruenrs of fungus-infected wood and lignin breakdown products. A sesquiterpenoid, isolated from fungus-infected wood was found to be attractive to the termite, Reticulitermes sp. Similarly extracts of the wood, Eucalyptus regnans was attractive to Nasuititermes spp. Controi of termites using a decayed wood block (which acted as an attractant) impregnated with a slow-acting insecticide to produce a toxic bait has been suggested. This method of bait blocks has been found useful in reducing the incidence of termites in buildings in residential areas in U. S. A. and Canada.

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