Rapid degradation of the Cry1F insecticidal crystal protein in soil

The gene for the core Cry1F insecticidal crystal protein (ICP) from Bacillus thuringiensis Berliner (Bt) has been incorporated into the genome of maize plants, Zea mays L. Plants expressing this ICP are protected from attack by various Lepidopteran pests including the European corn borer, Ostrinia nubilalis (Hübner). The stability of the Cry1F ICP in soil was assessed in a laboratory study designed to determine the persistence of the active protein residue in soil over time, using insect bioassay as the analytical quantification method. The GI(50) (concentration estimated to inhibit growth by 50%) rose at each consecutive incubation interval, indicating a consistent decline in Cry1F activity over time. The residue data were poorly described by a first-order model when fit to either the full data or a truncated data set where the last interval (28 days) was excluded. Data were well described by a shift-log model, and this model predicted DT(50) (time until 50% decay) and DT(90) (time until 90% decay) values of 0.6 and 6.9 days, respectively. This rapid degradation rate was consistent with other Bt proteins evaluated in our laboratory.