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Population Dynamics And Biological Control Of Elongate Hemlock Scale, Fiorinia Externa

Elongate hemlock scale (Fiorinia externa ) is an invasive species from Japan that was first detected in the United States in 1908 and has established in most states where eastern hemlock (Tsuga canadensis ) occurs. Scale density is much higher in the US (21 to >400 scales per 100 needles) compared to Japan (<1 scale per 100 needles) despite the presence in both regions of the parasitoid Encarsia citrina that has been assumed to be responsible for low densities in Japan. I have found that phenology of the vulnerable scale stage was asynchronous with E. citrina flight throughout the eastern United States. This asynchrony was the result of overlapping life stages and generations of elongate hemlock scale throughout the growing season. This overlap appears to result from delayed senescence of first generation adult females. To investigate the impact of E. citrina on elongate hemlock scale, natural enemy exclusion experiments were conducted. I found that E. citrina exerts some control on elongate hemlock scale, but insufficient to maintain density at levels seen in its native Japan. Existing records of parasitoids of elongate hemlock scale in Japan are limited to the Kyoto area. I sampled the parasitoid community of elongate hemlock scale and other scales on hemlock throughout Japan. Sequence data from two gene loci, 28SD2 and COI, were used to identify the number of unique parasitoid species attacking scales on Japanese hemlocks. This sequence data was also used to identify possible cryptic species within E. citrina in Japan. Twenty-two genetically distinct parasitoids were identified (seven singletons). Eleven (three singletons) of these were from elongate hemlock scale. With the exception of E. citrina , parasitoids tended to be host species specific. No evidence of cryptic species within E. citrina was found. The parasitoids identified dramatically increase the number of elongate hemlock scale parasitoids previously reported and this study may lead to the identification of several potential biological control agents of elongate hemlock scale for introduction to the United States.
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