Research just published in the Journal of Economic Entomology suggests that some western corn rootworm larvae may be able to detect small concentrations of certain Bt proteins in root tissue, stop feeding, and survive to the next instar.

Later instars of corn rootworm larvae are less likely to succumb to the Cry3Bb1 protein expressed in transgenic root tissue, says University of Illinois entomologist Mike Gray. Ultimately, under this scenario, there is adult emergence into producers' fields.

Corn rootworm emergence from fields planted to transgenic corn rootworm hybrids (MON 863, Cry3Bb1) has been reported many times previously. The authors of this paper correctly point out that it is "not entirely clear" how this occurs. Yet some larvae are surviving in fields planted to transgenic rootworm hybrids and emerging as adults in sufficient numbers to warrant scouting of fields for silk clipping in some instances.