Abell, K.J., & van Driesche, R.G. 2012 Impact of latitude on synchrony of a scale (Fiorinia externa) (Hemiptera: Diaspididae) and its parasitoid (Encarsia citrina) (Hymenoptera: Aphelinidae) in the Eastern United States. Biological Control 63:339–347

Notes: Elongate hemlock scale (EHS) (Fiorinia externa Ferris) is an invasive species from Japan that attacks eastern hemlock (Tsuga canadensis L. Carrière) and Carolina hemlock (Tsuga caroliniana Engelmann) in the United States. Scale density is much higher in the United States compared to Japan despite the presence in both regions of the parasitoid Encarsia citrina Crawford, the species assumed to be responsible for low scale densities in Japan. EHS and E. citrina have two distinct, synchronous generations in southern Japan (Kyoto), but only one and a half generations of EHS occur in the northeastern United States (Connecticut), and these are asynchronous with E. citrina flight. It has been hypothesized that good host-parasitoid synchrony explains low scale densities in Japan. If so, then it would follow that in the southern United States, where there are two full generations of the scale, there should be a seasonal pattern of hostparasitoid synchrony similar to that found in Kyoto. To test this hypothesis, sites in Connecticut, Pennsylvania, and North Carolina were sampled weekly in 2006 and 2007. We confirmed the presence of two full generations of EHS in North Carolina; however, phenology of the vulnerable scale stage (second instar) was still asynchronous with E. citrina flight and parasitism rates were lower than in either Pennsylvania or Connecticut. The primary reason for asynchrony appears to be the occurrence of overlapping life stages and generations of EHS, which is not seen in Japan. This overlap of scale generations appears to result from long life span of first generation adult females. Longer life span may be due to host quality. Our findings emphasize the importance of research to determine differences in the population dynamics of pest species in both the native and invaded range for biological control efforts. We identify regions in Japan with high climatic match to each of our study areas, which suggest locations for future natural enemy exploration.