Discrimination of Gypsy Moth Populations Based on Wing Venation

L.dispar Discriminant Scores

Log-likelihood discriminant scores for individual Russian Lymantria dispar wing membership in the Russian population, two Slovakian populations two North American populations and one Asian population. This plot is an output of the PLANAR software package available free by downloading from this site. The scores of each wing are connected by a line so that the highest discriminant score for that wing can be determined. In most cases the Russian wing obtained its highest score from the Russian Discriminant Function.

L.dispar Discriminant Scores

Log-likelihood discriminant scores for individual Slovakia 1991 Lymantria dispar wing membership as above. In most cases a Slovakian 1991 wing gets its highest discriminant score from one of the Slovakian discriminant functions. Slovakian 91 or 92 functions do not discriminate between one another.

L.dispar Discriminant Scores

Log-likelihood discriminant scores for Pennsylvania individual Lymantria dispar wing membership as above. In most cases the Pennsylvania wing gets its highest discriminant score from one of the USA discriminant functions. The MA and PA discriminant functions do not discriminate well between one another.

Key to population symbols in above trees

Preliminary analysis of our discriminant data

Each population of gypsy moths represents the animals collected from a single site. All populations are represented by a sample of at least 25 individual males. The average positions of the 13 wing landmarks in each population were used as the centers of elipsoidal confidence regions. Bivariate normality was assumed for each landmark. The landmarks were found to be relatively independent of each other and we proceded with the simple assumption that the landmarks are independent. Then, the discriminant score for each unknown wing was computed after fitting that wing to the average positions of the reference population. These calculations were accomplished using the PLANAR program, downloadable from this site. The resultant discriminant scores for each wing of a population can be represented as a line connecting its scores with respect to each reference population. Included here is a sample of the Russian population tested for its membership in 2 Slovakian, 2 North American and 2 Russian/Asian populations. As might be expected the Russian wings obtained their highest discriminant scores from the Russian Discriminant Function. When North American populations were tested in the same set of tests it was clear that North American populations obtained equivalently large scores from all North American Discriminant Functions. Tentatively, we conclude that one can discriminate between Asian, European and North American populations but that within North American or within European populations it is not possible to reliably predict from what sub-population a wing sample has been drawn.

Analysis of a more extensive set of populations, including the above set, are in preparation for publication. We are extending our analysis to use the new Thin Plate Spline suite of analytic software produced by F. James Rohlf and available through the morphometrics WWW site.

Stereo image of a principle component analysis of Thin Plate Spline analysed North American, European, Asian and Russian populations of forewing landmarks in shape space.   This stereo image was prepared with Mage from an analysis of averaged landmarks obtained using PLANAR. The Principle Components were extracted from the thin plate spline analysis using Rohlf's tpsRelw Ver. 1.07. Component scores 1, 2 and 6 are displayed. Single population averages of L. dispar from Asia and Russia and the outgroup species Lymantria obfusca are depicted as large spheres. The average populations of European and North American origin are also depicted as large spheres while smaller spheres represent individual populations within those regions. The '.kin' file of this image is available which allows identification of individual populations represented by each small sphere.
The cooperation and support of USDA APHIS in our developing the PLANAR software is acknowledged. Phil Kingsley of USDA APHIS shared with me the Pennsylvania (PA88 and PA89) and Asian (Asia) populations as well as the Lymantria obfusca wings. Bill Wallner, of USDA Forest Service, Northeastern Forest Experiment Station, Hamden, Conn., provided our Yakovlevka, Russia (Rus) population. The extensive Slovakian populations came from Julius Novotny of the Forest Research Institute at Banska Stiavnica, Slovakia.

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