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United States Department of Agriculture

Agricultural Research Service

Research Project: Production Management Research For Horticultural Crops in the Gulf South

Location: Southern Horticultural Research

Title: Carbon isotope ratios document that the elytra of western corn rootworm reflects adult versus larval feeding and later instar larvae prefer Bt corn to alternate hosts

Authors
item Hiltpold, Ivan -
item ADAMCZYK, JOHN
item Higdon, Matthew -
item Clark, Thomas -
item HIBBARD, BRUCE

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 14, 2014
Publication Date: May 1, 2014
Citation: Hiltpold, I., Adamczyk Jr, J.J., Higdon, M.L., Clark, T.L., Hibbard, B.E. 2014. Carbon isotope ratios document that the elytra of western corn rootworm reflects adult versus larval feeding and later instar larvae prefer Bt corn to alternate hosts. Environmental Entomology. 43(3):840-848.

Interpretive Summary: In much of the Corn Belt and parts of Europe, the western corn rootworm is the most important pest of corn. The need for additional basic knowledge of this pest has been highlighted while developing resistance management plans for insecticidal genetically modified crops. This study evaluated the possibility of tracking feeding habits of western corn rootworm larvae using carbon stable isotope signatures. Plants accumulate different ratios of 13C:12C, usually expressed as d13C, according to their photosynthetic pathway and herbivore biomass would be expected to reflect the d13C of the food they eat. For the current experiment, western corn rootworm larvae were grown on different species of plants exhibiting different d13C values. d13C values were then measured in elytra of the emerging beetle. When adults were unfed, biomass reflected larval feeding. When beetles were fed for 30 days post emergence as beetles, d13C values of elytra unexpectedly reflected adult feeding and masked larval feeding habits. These results suggest the use of caution in the interpretation of d13C data aiming to document western corn rootworm larval diet history if beetle feeding history is unknown. Western corn rootworm larval choice between corn with and without genetically modified (Bt) traits aimed at their control and alternate hosts was also assessed by recording adult emergence and measuring d13C values in unfed western corn rootworm beetles. Propensity for feeding on alternate hosts versus corn was biased toward feeding on corn regardless whether the corn had Bt or not, suggesting western corn rootowrm larvae did were not repelled by Bt. These data will be helpful for regulators in interpretting western corn rootworm feeding data on Bt corn.

Technical Abstract: The western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte, is a major pest of maize, Zea mays L., worldwide. While exploring conventional approaches to management and more recently bioengineering, extended research has been conducted on ways to manage its root-feeding larvae. The need for basic knowledge has been highlighted while developing resistance management models for Bt insecticidal GMO? crops and knowledge on the WCR basic biology is still lacking in certain areas. This study evaluated the possibility of tracking feeding habits of WCR larvae using carbon stable isotope signatures. Plants accumulate different ratios of 13C:12C, usually expressed as d13C, according to their photosynthetic pathway and herbivore biomass would be expected to reflect the d13C of the food they eat. For the current experiment, WCR larvae were grown of on different species of plants exhibiting different d13C values. d13C values were then measured in elytra of the emerging beetle. When adults were unfed, biomass reflected larval feeding. When beetles were fed for 30 d post emergence, d13C values of elytra unexpectedly reflected adult feeding and masked larval feeding habits. These results suggest the use of caution in the interpretation of d13C data aiming to document WCR larval diet history if beetle feeding history is unknown. WCR larval choice between isoline/Bt maize and alternate hosts was also assessed by recording adult emergence and measuring d13C values in unfed WCR beetles. Propensity for feeding on alternate hosts versus corn was actually biased toward feeding on corn, but more so for a mixture of alternate hosts and Bt corn than for a mixture of alternate hosts and isoline corn suggesting WCR larvae did were not repelled by Bt. Reasons why the measurement timeframe is important in these measurements are discussed.

Last Modified: 8/19/2014
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