RAPD variation within and among geographic populations of wheat stem sawfly (Cephus cinctus Norton)

Abstract

Little is known about the nature and extent of genetic diversity in wheat stem sawfly [Cephus cinctus Norton (Hymenoptera: Cephidae)], a destructive insect pest of wheat (Triticum aestivum L.) in the northern Great Plains. We used random amplified polymorphic DNA polymerase chain reaction (RAPD-PCR) to examine variation in 182 individual larvae from 15 natural populations in Montana, North Dakota, and Wyoming. Of the 60 amplified RAPD products from 20 random decamer primers used to characterize individuals, the band frequencies of 31 (52%) varied among collection sites. Each sawfly individual had a unique multiband RAPD phenotype. Analysis of molecular variance partitioned RAPD variation into among- and within-population components. In a combined analysis, the within-population component accounted for 71.6% of the variation and was significantly different from zero at the 1% probability level. Among-region (Montana versus North Dakota and Wyoming) and among-population components accounted for 22.1% and 6.3% of the total variation, respectively. Subset analyses of Montana and North Dakota groups indicated significant differences among Montana populations but not North Dakota populations. Pairwise tests for homogeneity of RAPD variance between populations suggested significant divergence among 81 of 105 (77%) population pairs, including all but three of the Montana population comparisons. A simple assay for developmental variation indicated that postdiapause larval development and subsequent wasp emergence under controlled conditions was longer in insects collected from North Dakota than in those collected from Montana.