Evaluation of damage caused by stalk borers, Sesamia spp. (Lepidoptera: Noctuidae), on sugarcane quality in Iran

The noctuid stalk borers, Sesamia spp. (S. cretica Led. and S. nonagrioides Lef.), damage a considerable percentage of sugarcane internodes annually in the province of Khuzestan, Iran. A study was conducted to quantify the relationship between stalk borer damage and sugar quality to estimate the monetary loss incurred at these levels of damage at harvest time. Three commercial varieties of sugarcane (SP70-1143, CP69-1062 and CP48-103) were studied to determine the effects of damage on sugar quality. Stalks were separated into seven groups: control (without damage); one to five bored internodes per stalk; and more than five bored internodes per stalk. The percentage of bored internodes and several parameters, such as pol and brix, were measured. Sugar in the control group was 123.78, 123.72 and 104.84 kg/ton for SP70-1143, CP69-1062 and CP48-103, respectively. Sugar per ton, juice purity, pol and brix were all significantly inversely correlated to the percentage of bored internodes. Estimated sugar losses for every 1% bored internode were 0.17, 0.39 and 0.23% (equal to 210, 482 and 241 kg sugar) in SP70-1143, CP69-1062 and CP48-103, respectively. These varieties could tolerate damage of up to 18.1, 11.7 and 18.9% bored internodes, respectively, compared to the control. Regression slopes for CP69-1062 were slightly higher than those of the other two varieties. Therefore, based on quality damage, CP69-1062 is susceptible to stalk borer damage.