Has resistance taken root in U.S. corn fields? Demand for insect control

Abstract

Corn farmers reported unexpectedly severe damage on fields planted with geneticallyengineered rootworm-resistant (Bt-CRW) corn seeds during the 2009 growing season. Entomologists later determined that rootworms on these fields had developed resistance to the insecticidal proteins produced by Bt-CRW corn. This article explores what corn farmers' seed and soil insecticide choices imply about rootworm resistance in the United States. First, a soil insecticide demand function is derived using a damage-abatement model. Next, this demand function is estimated using field-level data from 2005 and 2010. We find that rootworms (Diabrotica spp.) cost farmers approximately $1.3 billion in 2005 and $2 billion in 2010. When used, Bt-CRW seeds were very effective, reducing average yield losses by approximately five bushels per acre and providing over twice as much control (on average) as soil insecticides. We found no evidence that soil insecticide use was higher on fields where resistance was most likely to develop. However, we did find that demand for soil insecticides was elastic. These results suggest that rootworm resistance was not widespread in 2010, but that it could substantively increase soil insecticide use if it evolved and spread.