ESTIMATION OF POTENTIAL LOSSES FROM THE TOP-SHOOT BORER, SCIRPOPHAGA EXCERPTALIS WALKER (LEPIDOPTERA: PYRALIDAE) IN RAMU, PAPUA NEW GUINEA

THE TOP-SHOOT borer, Scirpophaga excerptalis Walker (Lep.: Pyralidae) is known from the Papua New Guinea mainland and its major off-shore islands. The larvae of S. excerptalis attack cane of all ages. In semi-mature to mature crops, bored cane suffers yield losses and even greater losses in cane juice quality. Damage levels observed in commercial cane at Ramu Sugar plantation for S. excerptalis have been as high as 7% or 8 000 to 10 000 bored stalks per ha. Significant negative correlations between bored cane and sucrose content were observed with up to 0.11% reduction in brix % juice and similar reductions in pol % juice observed for every 10% increase in damage. It was also observed that for every 10 cm increase in borer tunnel length, there was a corresponding decline of 1.2 units of pol % juice. To maintain high recovery of sucrose and efficient processing, the proportion of damaged cane delivered to the mill for processing should be less than 40%.