|HITCHON, ANDREA - University Of Guelph|
|SMITH, JOCELYN - University Of Guelph|
|SCHAAFSMA, ART - University Of Guelph|
Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2015
Publication Date: 5/21/2015
Citation: Hitchon, A.J., Smith, J.L., French, B.W., Schaafsma, A.W. 2015. Impact of the Bt corn proteins Cry34/35Ab1 and Cry3Bb1, alone or pyramided, on western corn rootworm (Coleoptera: Chrysomelidae) beetle emergence in the field. Journal of Economic Entomology. DOI: 10.1093/jee/tov125.
Interpretive Summary: Western corn rootworm is a major pest of corn. For three field seasons, we evaluated effects on adult beetle emergence, and comparing a non-Bt corn variety with varieties expressing three Bt toxic proteins singly (Cry3Bb1 or Cry34/35Ab1) and together (pyramid Cry3Bb1 plus Cry34/35Ab1). Each trial was artificially infested with western corn rootworm eggs and plots were covered with a screen tent to prevent beetles from escaping. Adults were collected twice weekly. In comparison to the non-Bt corn, we collected the fewest adults from the corn with the pyramided Bt proteins followed by Cry3Bb1 and then Cry34/35Ab1. Bt proteins reduced adult emergence by 64 to >99%. More females were recovered than males from corn expressing the Cry3Bb1 protein. Emergence was delayed in all Bt protein treatments when compared to the control, and was longest for the pyramided traits. The effect of Bt proteins on the emergence timing and sex ratio of western corn rootworm has implications regarding the suitability of resistance management plans, specifically the effectiveness of the refuge strategy. Delays in emergence between Bt and non-Bt refuge hybrids may mean males from the refuge are not available to mate with late emerging females from Bt corn hybrids. Scientists and policy-makers can use these results to design effective insect resistance management plans for corn rootworm.
Technical Abstract: Western corn rootworm, Diabrotica virgifera virgifera LeConte, is a major pest of corn, Zea mays L. This study compared the effect of the Bt proteins Cry34/35Ab1, Cry3Bb1, singly expressed, and Cry3Bb1 plus Cry34/35Ab1 in a pyramid, with a near-isoline control, on D. virgifera adult emergence in field trials in 2010, 2012, and 2013. Each trial was infested artificially with 2500 viable D. virgifera eggs per row-m and plots were covered with a screen tent. Beetles were collected twice weekly. The percent reduction of D.virgifera emergence compared with the control ranged from 64.3 to 97.4% in the Cry34/35Ab1 treatment, 91.1 – 95.2% in Cry3Bb1, and 98.1 – 99.6% in Cry3Bb1 plus Cry34/35Ab1 across environments. A higher female to male ratio was favored in adult emergence in plots expressing Cry3Bb1 singly or Cry3Bb1 pyramided with Cry34/35Ab1, but not Cry34/35Ab1 alone. The time to 50% emergence was delayed in all Bt treatments when compared with the control, and longest for the pyramided proteins. In 2013, three egg infestation levels were tested, and a density-dependent reduction in adult emergence was observed at 1250 viable eggs per row-m suggesting density-dependence likely played a role in earlier experiments. The effect of Bt proteins on the emergence timing and sex ratio of western corn rootworm has implications regarding the suitability of resistance management plans, specifically the effectiveness of the refuge strategy. Susceptible males emerging from the refuge might not be synchronized to mate with potentially resistant females emerging later from Bt corn hybrids.