Estimating the economic injury level and the economic threshold for the use of -cypermethrin against the sugarcane borer, Eldana saccharina Walker (Lepidoptera: Pyralidae)

Five years of data from insecticide trials that assessed the value of using -cypermethrin (Fastac) against the sugarcane borer Eldana saccharina Walker (Lepidoptera: Pyralidae) were used to estimate the economic injury level (EIL) and the economic threshold (ET) for this pest. The analysis was based on estimates of borer damage (percentage of internodes bored) and larval numbers, and the effect of these on estimated percentage recoverable sugar (ERC%) and tonnes ERC/ha. The EIL, based on percent internodes bored (%IB) and ERC%, was more reliable than estimates based on larval numbers and ERC%, and was estimated to be 5.8%IB (1.32) or 7.3%IB (1.65), depending on the level of treatment efficacy selected (50 and 40%, respectively). Where tonnes ERC/ha was used, estimated EIL was 9.3%IB (1.96) or 11.5%IB (2.45) for efficacy levels of 50 and 40%, respectively. Least reliable were estimates based on assessments of larval numbers. This was attributed to the weak association between larval populations and intensity of damage over time. Based on estimates of damage accumulation over time, the ET based on %IB and ERC% was estimated to be 2%IB, assuming a 40% treatment efficacy. Such estimates provide useful measures that can aid in deciding whether or not the use of an insecticide is justified.