Across the corn belt depending on time of year | Research has shown that once a resistance has been developed in an insect, it is usually there even after the toxin is removed from the insect's environment. The lack of soil insecticide resistance in rootworm is all about the huge non-exposure refuges (70-90% of the field).
When Bt-RW were first introduced, the kill of rootworm was not 100%. YieldGard RW (Cry3Bb1) has a survival rate of 4 beetles per sq ft. Herculex RW (Cry 34/35) has a survival rate of 2.5 beetles per sq ft and SmartStak (a combination of the two traits) had a beetle survival rate of 1 beetle per sq ft. It doesn't sound like much, but then multiply it times the # of sq ft in an acre (43,560) and you have a lot of surviving beetles when the traits were first introduced. This is where our rootworm resistance came from.
As tolerance to Bt increased, more beetles survived per sq ft and as the tolerant beetles inter-mated, tolerance increased to resistance. It is a sliding scale. |
rootworm damage on CRW corn paid for by seed companies
