Tolerance of eCry3.1Ab in reciprocal cross offspring of eCry3.1Ab-selected and control colonies of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Authors: GEISERT, RYAN - University Of Missouri; ELLERSIECK, MARK - University Of Missouri; Hibbard, Bruce

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/2/2015
Publication Date: 4/11/2016
Publication URL: http://handle.nal.usda.gov/10113/62299
Citation: Geisert, R.W., Ellersieck, M.R., Hibbard, B.E. 2016. Tolerance of eCry3.1Ab in reciprocal cross offspring of eCry3.1Ab-selected and control colonies of Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae). Journal of Economic Entomology. 109:815-820.

Interpretive Summary: The western corn rootworm is the most important insect pest of corn and has developed resistance to most control tactics used to manage it including transgenic corn varieties that express insecticidal Bt proteins. Because of this, it is important to evaluate resistance dynamics in the western corn rootworm to the newest Bt protein targeting rootworm before extensive selection in the field. This experiment was conducted in order to determine if inheritance of the laboratory-selected resistance trait to this product was recessive, dominant or something in between. In order to determine this, two colonies were created by crossing virgin western corn rootworm from 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 Bt expressing corn and corn without Bt in greenhouse experiments, seedling assays, and diet assays with increasing doses of Bt being applied to the surface of artificial diet. Results indicated that the resistance trait was dominantly inherited in the western corn rootworm. Resistance management tactics assume recessive inheritance. Slowing the spread of any dominant trait will be especially difficult, so any field-selected resistance to this trait that might develop should be monitored closely.

Technical Abstract: Two reciprocal cross colonies were created by separating virgin western corn rootworm, Diabrotica virgifera virgifera LeConte, males and females from both a selected laboratory colony that was being reared on eCry3.1Ab-expressing corn (Zea mays L.) and a control colony reared on its near isoline. Females from the selected colony were paired with males of the control colony and vice versa to create both a selected female by control male colony (Sel') and control female by selected male colony (Con'). Both colonies along with their parental colonies (eCry3.1Ab-selected and control) were evaluated on eCry3.1Ab-expressing corn and it’s near isoline in greenhouse experiments, seedling assays in growth chambers, and diet toxicity assays with increasing doses eCry3.1Ab being applied to the surface of artificial diet for western corn rootworm larvae. Statistical analysis of larval recovery, adult recovery, and plant root damage in greenhouse experiments showed no significant colony × corn interaction but did show a significant main effect of corn type. Similar results were seen for larvae recovery from the seedling assays with only a significant main effect of corn type being found. Results from the diet toxicity assays showed the control colony to have a significantly lower LC50 value than the selected and cross colonies and a significantly lower EC50 than the selected and Con' colonies. Calculations of dominance values (h) of eCry3.1Ab resistance traits from seedling assays indicated that the two reciprocal cross colonies to have a dominance value (h) of approximately 1, suggesting dominance of the eCry3.1Ab resistance trait. Data from these experiments help to showcase how eCry3.1Ab resistance traits can be transferred between resistant and susceptible western corn rootworms.