Differentiation between forms of Lymantria dispar
Studies have been carried out in Germany to differentiate between forms of Lymantria dispar, as it has been suggested that the last outbreak of gypsy moth in Europe could be the result of an introduction or migration of L. dispar from Asia. In United States, introductions of gypsy moths from Asia have been reported (EPPO RS 94/136) and American scientists have observed that these insects had a broader host range and that females had better flying capabilities.
A first series of cluster analysis with RAPD patterns has been performed with specimens of L. dispar originating from 15 habitats in Germany (Hessen, Baden-Württemberg, Sachsen, Bayern, Niedersachsen, Nordrhein-Westfalen, Brandenburg, Sachsen-Anhalt), and 8 habitats ranging from Russia (Ulyanovsk, Tatarstan) and Kazakhstan, to Asia (Manchuria, eastern China, south-eastern China and Japan). Cluster analysis was performed on data sets with increasing numbers of RAPD characters using a total of five different random primers. When studying 12 to 16 characters obtained with a single primer, a separation was obtained between Asian and European populations but with occasional appearance of one to three Asian populations in the European branch of the dendrogram. When studying 72 characters obtained with 5 primers, a clear separation was obtained between Asian and European provenances. In addition, the geographical origin was reflected in the order of the phylogenic tree, e.g. all specimens from Hessen were clustered together, and Asian populations were predominantly clustered correctly.
A second series of cluster analysis was performed on 5 individuals of the Tatarstan population detected in the European branch and 14 individuals from a Hessen population. In addition, L. dispar from Spain and L. monacha were included in this study as references. Evaluation of 28 characters obtained with two primers again resulted in strict separation between the Tatarstan and Hessen populations. Genetic differences between L. dispar samples ranged from zero to approximately 30 %, and the difference between L. monacha and L. dispar was 96 %. Analogous experiments are under way comparing individuals from other German outbreak areas (e.g. Baden-Württemberg) with those of an Asian provenance.
The occasional appearance of Asian provenances in the European branch of the dendrograms should be regarded as marginal similarities since they were only obtained when small numbers of RAPD characters were evaluated. The results obtained so far do not support the hypothesis of an introduction of gypsy moth genotypes from Asia into Europe.
Sources
Graser, E.; Wulf, A.; Burgermeister, W. (1996) Genetic distances between Asian and European Lymantria dispar populations revealed by cluster analysis of RAPD patterns.
Nachrichtenblatt des Deutschen Pflanzenschutzdienstes (in preparation)