Allozyme Variation in Hemlock Woolly Adelgid (Hemiptera: Adelgidae) From the United States and China

Thehemlockwoolly adelgid,Adelges tsugaeAnnand(Hemiptera:Adelgidae), is amajor introduced pest of eastern hemlock, Tsuga canadensis (L.) Carrière. Hemlock woolly adelgid in the UnitedStates is anholocyclic andanobligateparthenogen, becauseno suitableprimaryhost (onwhich sexual reproduction occurs inAsia) is reported for this adelgid in theUnited States. Allozyme analyses were conducted to assess the relatedness between three hemlock woolly adelgid populations in the eastern United States (Connecticut, New Jersey, and Virginia) and to compare them with adelgids fromthewesternUnitedStates (Washington)andChina. SigniÞcanthemlockwoolly adelgid allozyme variation was found between nonadjacent trees within a site in the eastern United States. There was a small difference between the twonorthern and the southern populations despite the relative genetic uniformity between the sites across the allozyme loci evaluated. There were low numbers of protein alleles in the eastern populations, whereas thewestern andChinese populations had additional alleles not found in the eastern populations. Both heterozygote excesses and deÞcits were detected as would be expected in populations that are not randomlymating. There were only a few abundant genotypes and they tended to be more homozygous than the rarer genotypes. The hemlock woolly adelgid population from China that is cyclically parthenogenic was more genetically diverse than the other hemlock woolly adelgid populations that are presumed to be obligately parthenogenic. Allozymes provide some useful information about genetic variation in hemlock woolly adelgid but seem to be less suited to assess actual genetic diversity and structure of populations because of the small size of the hemlock woolly adelgid.