Economic injury level and sampling method of the oriental tobacco budworm, Helicoverpa assulta Guenee (Lepidoptera: Noctuidae), on hot peppers

Abstract

The occurrence pattern of the oriental tobacco budworm (OTB), Helcoverpa assulta Gueene (Lepidoptera: Noctuidae) was studied using sex-pheromone traps in hot pepper fields in Suwon, Pyeongteak in 2003 and 2004, and in Hamyang in 2003. Two types of occurrence pattern were found, and were characterized by a degree-day model using Weibull fuction. First type of model was developed with data in which the cumulative degree-days were 1,700 DD in the early October (General case). A validation was conducted using the data from the Horticultural Research Institute in 2003. The differences between model predictions and the observed data were 4, 5, and 10 days in 10, 50 and 90% occurrence levels, respectively.. The second type of model was developed with data in which cumulative degree-days were 1,900 DD in the early October (Special case). A validation was conducted using the data from the Horticultural Research Institute in 2001. The differences between model predictions and the observed data were 10, 1, and 0 days in 10, 50, and 90% occurrence levels, respectively. To develop economic injury level (EIL) of H. assulta on hot peppers, four steps of development process were taken. First, relationship between the number of larvae and the number of damaged fruits per plant was determined. Then, several studies were conducted to standardize the damaged pepper fruits per larva. The proportion of each length class for damaged fruits and the length of damaged fruits and the relationship between the length and the dry weight hot pepper fruits were used for the standardization. Third, each factors of economic injury level (EIL) was determined. Finally, EIL was developed using the determined factors. An experiment was conducted for the validation of the developed EIL at Suwon in 2004. Economic threshold (ET) was developed using three different methods which were the method of equilibrium proportion of EIL, the method of finding ET at a certain level of total production and the highest net profit method.