Reproduction and Adaptation of Exotic Hemlock Scales (Homoptera: Diaspididae) on Their New and Native Hosts

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Abstract
The feeding sites and reproductive success of two Japanese armored scales, Fiorinia externa Ferris and Nuculaspis tsugae (Marlatt) (Homoptera: Diaspididae), on native and exotic hemlocks were appraised in an arboretum and in a field plot in Connecticut during 1981. Fecundity of both scales was significantly higher on native Japanese hemlocks. Tsuga diversifolia Masters and T. sieboldii Carriere, than on the two North American species, T. canadensis (L.) Carriere and T. caroliniana Engelmann, in the arboretum. Similarly, fecundity was significantly higher on T. sieboldii than on T. canadensis in the field plot. Feeding sites of these scales were not segregated on either host; nymphs of both scales colonized the undersides of the youngest needles most often. Higher reproductive success of scales on Japanese than on North American hemlocks could not be attributed to scale density, to concentrations of nitrogen and water in the young needles, or to hemlock growing conditions. Fecundity of both scales on T. canadensis and T. sieboldii was significantly greater among scales whose mothers had been reared on the same species than among scales whose mothers had been reared on the other species. Data revealed that F. externa (in 12 generations) and N. tsugae (in 24 generations) had adapted to the specific attributes of trees growing less than 10 m apart. such that scale populations on these trees had become qualitatively different.