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This research assesses the potential for using different economic injury thresholds in management of a key insect pest on susceptible and resistant commercially produced cultivars of sugarcane (Saccharum spp. hybrids). In a 2-yr sugarcane borer, Diatraea saccharalis (F.) (Lepidoptera: Crambidae), study involving four commercially produced sugarcane cultivars and four insecticide treatment thresholds, 'LCP 85-384' and 'HoCP 91-555' were the most susceptible based on percentage of bored internodes compared with the more resistant 'HoCP 85-845' and 'CP 70-321'. In 2001, the 10% infested stalks threshold was not as effective as the 5% early season-10% late season and 5% full season for HoCP 91-555. Based on D. saccharalis injury under natural infestation conditions, susceptible cultivars seem to require a lower infestation threshold than the more resistant cultivars to achieve adequate injury reduction. Among yield components, only the theoretical recoverable sugar per stalk was significantly increased by applying insecticides. With the resistant HoCP 85-845, differences were not detected for percentage of bored internodes among treated versus untreated management regimes. The resistant HoCP 85-845 had higher levels of fiber in our study; however, no clear pattern on resistance mechanisms was established, because the resistant cultivar CP 70-321 had comparatively low levels of fiber. The development of cultivar-specific thresholds is expected to lower the amount of insecticide used for D. saccharalis management in the sugarcane industry, reduce selection pressure, and delay the development of insecticide resistance. © 2006 Entomological Society of America.

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Journal of Economic Entomology

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