INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Variation in Performance on cry1Ab-Transformed and Nontransgenic Rice Varieties Among Populations of Scirpophaga incertulas (Lepidoptera: Pyralidae) from Luzon Island, Philippines

We quantiÞed variation in performance under greenhouse conditions among seven populations of Scirpophaga incertulas (Walker) from Luzon Island, Philippines, on three rice varieties: ÔIR58Õ transformed with the cry1Ab gene from Bacillus thuringiensis Berliner, and nontransgenic IR58 and IR62. On IR62, S. incertulas performance did not differ among provinces for any of the 10 parameters measured, but there was a signiÞcant effect of town within province for one parameter, 20-d-old larvalweight.Larval survival after 48hon cry1Ab-transformedIR58didnotdiffer signiÞcantly among provinces, but did differ signiÞcantly among towns within a province. There was no geographic variation in larval survival after 48 h on control plants of IR58. Surviving insects from the cry1Ab-transformed IR58 were transferred to IR62 to complete development. There was no geographic variation in the percentage of insects completing development to adult emergence and the time required by the transferred female insects to complete development. However, there was variation among provinces in male developmental time. The absence of geographic variation on nontransgenic IR58 and the very limited variation on IR62 indicated that there was little variation in general vigor among the S. incertulas populations and thus that the variation in performance on cry1Ab-transformed IR58 was probably attributable to differences in susceptibility to Cry1Ab.