A Method of Predicting the Defoliation Threat to Pines by the Pine Tree Emperor Moth, Nudaurelia cytherea, by Counting Dead Moths on the Forest Floor

Abstract

SYNOPSIS A method enabling the early determination of the future defoliation threat to pine trees by larvae of the pine tree emperor moth, Nudaurelia cytherea, is presented. The method is based firstly on the determination of the number of larvae, derived from the number of dead moths present on the forest floor after the termination of their flying season, which can be expected in a particular stand and secondly on the determination of the amount of foliage available as food for the larvae concerned; these data, together with those obtained from earlier studies, are combined in a formula which enables a prediction of the percentage defoliation threat that can be expected in a particular stand. A figure enabling the direct reading of the amount of foliage of Pinus radiata, ranging from 2 to 20 m in height, is given. The method has been tested successfully in some plantations in the Western Cape. It is accepted that with further field experience modifications to the formula may be required.