EVALUATION OF BIOLOGICAL-ACTIVITY OF BACILLUS-THURINGIENSIS TEST SAMPLES USING A DIET INCORPORATION METHOD WITH DIAMONDBACK MOTH, PLUTELLA-XYLOSTELLA (LINNAEUS) (LEPIDOPTERA, YPONOMEUTIDAE)

Bioactivity of 2 test samples (KM301 and KM202) in wettable powder form which contain delta-endotoxin of Bacillus thuringiensis was evaluated by a diet incorporation method with a laboratory colony of the diamondback moth larvae, Plutella xylostella. Time-mortality curves and time-LC50 curves for the 2 samples were differed from each other. KM301 showed relatively rapid lethal activity in 2-3 days and KM202 had slower lethal activity in 3-14 days. However, time-pupation curves and time-EC50 (based on pupation inhibition) curves were not different from each other except in applied dose levels. When the bioactivity of the 2 samples was compared based on LC50, the relative potency of KM202 differed from KM301 depending on the day on which the mortality rates were determined. Compared with KM301, the bioactivity of the KM202 was lower at 2-3 days, similar to it at 4 days, and higher at 5-14 days. However, an evaluation based on EC50 showed that the KM202 was always superior to the KM301, regardless of reading days. The bioactivity of 2 samples evaluated by both diet incorporation and the leaf dip methods showed little difference between them, indicating that the relative potency was not changed by the bioassay methods.