SCREENING FOR BORER RESISTANCE AMONG SUGARCANE VARIETIES IN PAPUA NEW GUINEA, 2003–2008

COMMERCIAL CROPS of sugarcane at Ramu Agri-Industries, Papua New Guinea, are attacked by several species of moth borers, including Sesamia grisescens, Chilo terrenellus and Scirpophaga excerptalis, as well as the sugarcane weevil borer Rhabdoscelus obscurus. The three moth borers are not present in Australia but are a biosecurity risk. We analysed the results of two variety trials planted in 2003 and 2007 with the aim of evaluating varietal responses to these borers, and particularly to S. grisescens. For two moth borers, S. grisescens and S. excerptalis, and for the weevil borer, damage and/or numbers differed significantly among clones in at least one trial. However, varietal differences were not detected for C. terrenellus. There was a negative correlation between damage from C. terrenellus and S. grisescens in one trial and it is possible that damage from the latter species may interfere with the activities of C. terrenellus or destroy evidence of its presence. Damage from S. grisescens and weevil borers was positively correlated, probably because weevil borers are known to be attracted to previously damaged cane. Cane yield was measured in one trial and was negatively correlated with damage from S. grisescens and weevil borers but not from C. terrenellus or S. excerptalis. This study confirms the importance of S. grisescens as a major pest of sugarcane and a key component of the borer complex in PNG, confirms the existence of resistance to this pest among sugarcane clones, and indicates that screening of Australian commercial varieties for resistance to S. grisescens in PNG is worthwhile. Apparent varietal differences in crop response to borers in PNG may be influenced by interactions among species.