ARS | Publication request: Selection for resistance to mCry3A-expressing transgenic corn in western corn rootworm

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 3, 2011
Publication Date: June 1, 2011
Citation: Meihls, L., Higdon, M.L., Ellersieck, M., Hibbard, B.E. 2011. Selection for resistance to mCry3A-expressing transgenic corn in western corn rootworm. Journal of Economic Entomology. 104(3):1045-1054.

Interpretive Summary: The study and development of colonies of corn rootworms resistant to transgenic corn that carry an insecticide can help us understand how such resistance occurs and help us to slow resistance in current and future control measures. A laboratory colony of the western corn rootworm was established from field survivors of transgenic mCry3A-expressing corn. The mCry3A is an insecticidal protein derived from a bacteria and engineered to be expressed in corn. Feral adults emerging from transgenic corn and non-transgenic controls field plots were collected and returned to the laboratory for rearing and colony development. Two colonies were developed including a “selected” colony (from adults isolated and grown on transgenic corn) and a “control” colony (from adults isolated and grown on control corn). Testing in both greenhouse and the field demonstrated that the “selected” colony survived on both transgenic and control corn plants and did equal damage to both. The control colony survived significantly better on control corn than transgenic corn. The physiological resistance to the insecticidal protein for larvae from each colony in laboratory tests were only different after ten generations of selection. Laboratory-selected resistance has developed in western corn rootworm populations to all insecticidal proteins currently registered for corn rootworm management, which emphasizes the importance of adhering to resistance management plans for maintaining product efficacy.

Technical Abstract: To investigate the development of resistance to mCry3A, a laboratory colony of the western corn rootworm, Diabrotica virgifera virgifera LeConte, was established from field survivors of mCry3A-expressing (MIR604) corn. Feral adults emerging from MIR604 (selected) and isoline (control) field plots were collected and returned to the laboratory. Progeny of each colony was reared one generation on isoline corn and then crossed reciprocally with a nondiapausing colony. The resulting nondiapausing progeny were then reared on greenhouse corn in accordance with the wild type parent’s origin (on MIR604 or isoline corn). Following three additional generations of selection in the greenhouse, colonies were screened on MIR604 and isoline corn in the greenhouse. Larval survival of the selected colony was similar on isoline and MIR604 corn, while larvae of the control colony had significantly greater survival on isoline corn. The selected and unselected colony had similar survival on MIR604 corn. After a total of seven generations of selection, selected and control colonies were screened on MIR604 and isoline corn under field conditions. For the selected colony, there was no significant difference between larval survival on or damage to MIR604 and isoline corn while the control colony had significantly greater survival on and damage to isoline corn than MIR604. Again, the selected and unselected colony had similar survival on MIR604 corn. Additionally, larvae of the selected colony produced significantly less damage to isoline corn than larvae of the control colony on isoline corn roots. LC50 values of the selected and control colonies were not significantly different after a total of four generations of selection, but after six additional generations of selection, the resistance ratio of the selected colony was 15.4. Resistance has developed in western corn rootworm laboratory colonies to all Bt proteins currently registered for corn rootworm management, which emphasizes the importance of adhering to resistance management plans for maintaining product efficacy.