Ancient and modern colonization of North America by hemlock woolly adelgid, Adelges tsugae (Hemiptera: Adelgidae), an invasive insect from East Asia

Abstract

Hemlock woolly adelgid, Adelges tsugae, is an invasive pest of hemlock trees (Tsuga) in eastern North America. We used 14 microsatellites and mitochondrial COI sequences to assess its worldwide genetic structure and reconstruct its colonization history. The resulting information about its life cycle, biogeography and host specialization could help predict invasion by insect herbivores. We identified eight endemic lineages of hemlock adelgids in central China, western China, Ulleung Island (South Korea), western North America, and two each in Taiwan and Japan, with the Japanese lineages specializing on different Tsuga species. Adelgid life cycles varied at local and continental scales with different sexual, obligately asexual and facultatively asexual lineages. Adelgids in western North America exhibited very high microsatellite heterozygosity, which suggests ancient asexuality. The earliest lineages diverged in Asia during Pleistocene glacial periods, as estimated using approximate Bayesian computation. Colonization of western North America was estimated to have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan, perhaps carried by birds. The modern invasion from southern Japan to eastern North America caused an extreme genetic bottleneck with just two closely related clones detected throughout the introduced range. Both colonization events to North America involved host shifts to unrelated hemlock species. These results suggest that genetic diversity, host specialization and host phylogeny are not predictive of adelgid invasion. Monitoring non-native sentinel host trees and focusing on invasion pathways might be more effective methods of preventing invasion than making predictions using species traits or evolutionary history.

Ecological factors influencing the beneficial endosymbionts of the hemlock woolly adelgid (Hemiptera: Adelgidae)

“…Within life stages, samples were chosen so that half were infected with S. symbiotica and the remainder were not. All NY samples analyzed had identical microsatellite genotypes, which were also the same as the clonal genotype found throughout eastern United States (Havill et al ., ). This indicated that the absence of S. symbiotica in some A. tsugae individuals is likely not the result of two separate introductions of A. tsugae .…”

Dynamic Acquisition and Loss of Dual-Obligate Symbionts in the Plant-Sap-Feeding Adelgidae (Hemiptera: Sternorrhyncha: Aphidoidea)

“…Pseudomonas adelgestsugas’ symbionts and Adelges tsugae hosts from five genetically divergent populations [genetic divergence among A. tsugae suggests some populations may be distinct species (Havill et al, 2006, 2016)]. Phylogeny of ‘Ca.…”

“…Pseudomonas adelgestsugas’ symbionts (left) was estimated from 16 S rRNA sequences. A. tsugae phylogeny (right) was simplified from Havill et al (2006) and Havill et al (2016), in which all population-level nodes were significantly supported. Sample from Taiwan is new to this study.…”

A Little Bug with a Big Bite: Impact of Hemlock Woolly Adelgid Infestations on Forest Ecosystems in the Eastern USA and Potential Control Strategies

“…Eight distinguishable HWA linages that vary in life cycle, historical biogeography, and host specialization are identified. The lineage of western North America demonstrated higher genetic variation than those in eastern North American, Japan, and Mainland China [20,21]. This suggests the colonization of western North America might have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan (perhaps carried by birds, rather than through active dispersal of winged adelgid adults, which are not strong enough to travel across long distances like the Bering land bridge in order to colonize western North America).…”

“…This suggests the colonization of western North America might have occurred prior to the last glacial period by adelgids directly ancestral to those in southern Japan (perhaps carried by birds, rather than through active dispersal of winged adelgid adults, which are not strong enough to travel across long distances like the Bering land bridge in order to colonize western North America). In contrast, only one haplotype was identified in all HWA samples in eastern North America (from Massachusetts to West Virginia) and the haplotype was the same as those collected from hemlock ( T. sieboldii ) of Honshu, Japan, indicating that modern invasion of HWA in eastern North America originates in southern Japan [20,21]. This lack of genetic diversity of HWA in eastern North America, and its ability to reproduce asexually may be beneficial for its colonization because HWA will be more likely to establish without the constraint of finding mates in low population density locations [22].…”