Arboriculture & Urban Forestry 40(3): May 2014 mainly presented the findings quantitatively with a concluding list of susceptible species, and without a qualitative description of how these conclusions were reached. For example, Yang (2005) and Yin and Lu (2005) reviewed Chinese research concern- ing ALB but presented the findings very briefly and without an introduction to the methodology and approach used in the studies. This might be the rea- son why there are some contradictions regarding the suitability of different species and genera in Appen- dix 1. Furthermore, it is oſten unclear whether the findings listed in the appendices and Table 2 refer to damage by adult beetles, as specified by Ludwig et al. (2002), Morewood et al. (2003), and Morewood et al. (2004a), or refer to use of the trees for oviposition and larval development. Such information is rarely presented in the publications reviewed, which weak- ened the information and leads to further confusion. In the compilation of host trees for the two long- horned beetles, there was a rather large amount of information concerning tree genera, which of course include many more species than those listed in the appendices and Table 2. Including whole genera as a host, for example, CLB may cause the use of a whole genus to be banned, even if there are just a few spe- cies that are susceptible and the rest are resistant or rarely affected. When interpreting information from one study in another, it is tempting to simplify the information. An example is Van der Gaag et al. (2010), presenting a list of hosts for CLB based on original data in Lingafelter and Hoebeke (2002), most of which was in turn based on information in Chinese and Japanese studies (Appendix 3). Lin- gafelter and Hoebeke (2002) listed a large number of species as hosts for CLB, but in the compilation by Van der Gaag (2010), much of this species infor- mation was changed to whole genera, without fur- ther information. This simplification of host-related information can result in great confusion and mis- understanding, especially if it is used by national authorities to formulate recommendations on trees to avoid in example urban environments. The pres- ent review uncovered clear evidence that there are species within highly susceptible genera that are resistant or rarely affected. For example, Williams et al. (2004) evaluated 12 maple species in native com- munities of South Korea for ALB damage and found that only five species (three native and two invasive exotic species) had visible damage or adult ALB, 147 leaving seven species with no observed damage. Furthermore, even within the poplar genus, which is considered the most susceptible to ALB, there is evidence that sections within this genus are resis- tant or rarely affected (Weilun and Wen 2005). In a compilation by Hu et al. (2009) based on data from Yin and Lu (2005) and Gao et al. (1997), poplar spe- cies belonging to the section Turanga (e.g., Populus pruinosa Schrenk) and Populus (e.g., Populus alba L., P. tomentosa Carr., and P. tremula L.) were listed as less susceptible or slightly resistant to ALB (Bao et al. 1999; Table 2). These examples of resistant spe- cies within highly susceptible genera might indicate that there has been generalization regarding the species and genera classified as hosts. If several spe- cies have been shown to be susceptible to ALB, it is easy to conclude that the whole genus is susceptible. The fact that the first discovery of longhorned beetles outside their native range took place in 1996 in New York (ALB) (Lingafelter and Hoebeke 2002) is reflected in the geographical focus of the publica- tions reviewed. ALB host-related publications older than 1996 were mainly produced in China, Japan, and Taiwan (Appendix 3), while publications later than 1996 had a greater focus on North America. CLB host-related publications later than the year 2000 mainly had a European focus, following the first recognized outbreak in Europe (Appendix 3). Information about whether a tree species is a host, good host, or very good host was fairly com- monly provided in the literature reviewed. However, it was more difficult to find clear definitions of the terms used to describe the kind of damage done by the beetles to the tree. Terms used commonly in the literature were: infested, attacked, host, and feeding. For the beetles to become established in an area they not only need to find food, but also to be able to propagate, which means finding suitable tree species for oviposition and larval development into fully developed beetles. Ric et al. (2006) noted that not all tree species are suitable for the whole reproduction cycle. For example, some species are suitable for oviposition but not larval development. Other species are used for feeding by the adult beetles but not for oviposition. The terms infested, attacked, host, and feeding do not clearly describe whether the tree is used for feeding by adults or whether full larval development is possible. Haack et al. (1997) used “primary host tree” and “occa- ©2014 International Society of Arboriculture
May 2014
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