Rapid degradation of a binary, PS149B1, delta-endotoxin of Bacillus thuringiensis in soil, and a novel mathematical model for fitting curve-linear decay
Authors: Herman, R.A., Scherer, P.N., Wolt, J.D.
Journal, Volume, Year: Environmental Entomology, volume 31(2):208-214, 2002
A binary Bt protein was examined in a soil degradation study using a southern corn rootworm (Diabrotica undecimpunctata howardi) bioassay. The protein was microbially-produced and the soil was an agronomic soil. The soil was fortified to 5 mg of each protein per gram of soil, which is about 4 times the expected amount in the field. This was necessary to provide the biological activity level needed for the bioassay to work. The bioassay used weight change as a reporter and dead insects were excluded from the assay. The data was originally fit to a first order model, but it was not satisfactory, so a three-parameter, biexponential model. The new model predicted a dissipation time for 50% (DT50) of 2.4 days. A shift-log model, a first order model, and the biexponential model were compared for data sets on other pesticides and Bt proteins.
This study did not look at the degradation process from the standpoint of a plant decaying in soil, nor use the plant-produced protein, but it was a good study using the purified protein. The need to use an environmentally unrealistic amount of protein in order to use the bioassay shows the limitations of bioassay and the need for a more chemically-based method. The comparison of different models for degradation is of interest.