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Title: Development and characterization of MIR604 resistance in a western corn rootworm population (Coleoptera: Chrysomelidae)

Author
item Meihls, Lisa
item FRANK, DANIEL - University Of West Virginia
item ELLERSIECK, MARK - University Of Missouri
item Hibbard, Bruce

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2015
Publication Date: 4/11/2016
Publication URL: http://handle.nal.usda.gov/10113/62319
Citation: Meihls, L.N., Frank, D.L., Ellersieck, M.R., Hibbard, B.E. 2016. Development and characterization of MIR604 resistance in a western corn rootworm population (Coleoptera: Chrysomelidae). Environmental Entomology. 45:526-536.

Interpretive Summary: Transgenic corn that expresses its own insecticide (a protein knows as Bt toxin) has been developed targeting the western corn rootworm, the most serious insect pest of corn. This pest has developed resistance to most management tactics targeting it including two types of Bt toxins. The mCry3A Bt protein is one of only four Bt toxins currently available for rootworm management. Utilizing a colony of western corn rootworm selected for resistance to mCry3A, we evaluated how mCry3A resistance was inherited and whether fitness costs were associated with mCry3A resistance. In order to determine this, two colonies were created by crossing virgin western corn rootworm from the resistant laboratory colony with virgin western corn rootworms from a control colony that was not resistant to Bt. Both new colonies along with their parental colonies were evaluated on mCry3A-expressing Bt corn and corn without Bt in greenhouse experiments, seedling assays, and diet assays with increasing doses of mCry3A being applied to the surface of artificial diet. Heritability data suggested that the resistance traits were inherited in dominant/non-recessive manner. When the selected colony was removed from selection pressure and evaluated resistance was comparable to that of the selected colony. The persistence of resistance in the population in the absence of exposure to mCry3A suggests that there are few negative effects on the insect for having this resistance trait. Since the resistance trait is inherited in a dominant manner and is associated with few negative effects, the trait will persist in the population for an extended period regardless of additional selection. Special diligence will be required to delay resistance to this product in the field.

Technical Abstract: mCry3A is one of only four proteins licensed for commercial use in Diabrotica control. Utilizing a colony of western corn rootworm, Diabrotica virgifera virgifera LeConte, selected for resistance to mCry3A, we evaluated how mCry3A resistance was inherited and whether fitness costs were associated with mCry3A resistance. Reciprocal crosses between the selected colony and a control colony were performed, and resulting progeny along with parent colonies were evaluated in dose toxicity assays, greenhouse assays, and seedling assays. Dose toxicity assay results were inconclusive, as the highest dose of protein tested did not produce sufficient mortality for accurate LC50 calculation. In greenhouse whole plant assays on mCry3A-expressing corn, larval relative survival of the selected female × control male reciprocal cross was similar to that of the selected colony, while that of the control female × selected male was intermediate between the mCry3-selected colony and the control colony. However, when adult relative survival in greenhouse whole plant assays was examined, no significant difference between the two reciprocal crosses and the two parent colonies was detected. Heritability calculations based on both larval (0.66) and adult (1.03) survival data indicate that resistance to mCry3A is not inherited in a recessive manner. The selected colony was removed from selection pressure and evaluated after three or eight generations of removal. At three generations of removal from selection, a slight decrease in larval relative survival was detected compared with the selected colony. At eight generations of removal from selection, larval relative survival was comparable to that of the selected colony.