Monday, December 11, 2006

Confirmation of a Cry1Ab-resistant sugarcane borer strain on Bt corn plants in Louisiana

Xiaoyi Wu, xwu3@lsu.edu1, Fangneng Huang, fhuang@agcenter.lsu.edu1, B. Roger Leonard, rleonard@agcenter.lsu.edu2, and H. Moore Steven3. (1) Department of Entomology, LSU AgCenter, Baton Rouge, LA, (2) Macon Ridge Research Station, LSU AgCenter, Winnsboro, LA, (3) Dean Lee Research Station, LSU AgCenter, Alexandria, LA

A Cry1Ab-resistant sugarcane borer (SCB) strain, was selected via F2 screening procedures and confirmed on transgenic Bacillus thuringiensis (Bt) corn plants in Louisiana. Larval survival of Bt-susceptible, heterozygous, and resistant SCB strains was recorded on five non-Bt corn and seven Bt-corn hybrids at two vegetative (V6-V8, V9-V10) and two reproductive (VT-R1, R2-R3) stages, respectively, in 2005 and 2006 in greenhouse tests. Twenty neonates were released on each plant and larval survival was checked 21d after infestation. Larval survival rates of resistant SCB were 14.3%, 9.6%, 24.5% and 18.1% respectively at the four plant growth stages. Regardless of growth stage, survival of the resistant SCB was significantly higher than that of the susceptible and heterozygous SCB on Bt-corn plants. Furthermore, the survival rate of heterozygous SCB was higher than that of the susceptible insect at all developmental stages of Bt-corn plants. No significant differences among the survival rates of the three insect strains were observed on the non-Bt corn hybrids at the V9-V10 stage. However, survival rates of both heterozygous and resistant larvae were higher than that of the susceptible larvae on non-Bt corn hybrids at the other three stages. The results also indicated that the survival rates were low when neonates were infested on the V6-V8 stage Bt-corn plants. During later vegetative stages (>V8), SCB survival rates increased, and may be the result of lower Bt-toxin expression in older plants. Nevertheless, during the reproductive stage (R2-R3), SCB larval survival gain decreased. This effect may be related to the poor nutrition status or hard stalks of those plants rather than Bt-protein expression.

Species 1: Lepidoptera Crambidae Diatraea saccharalis (sugarcane borer)