Arboriculture & Urban Forestry 40(3): May 2014 In total, 35 publications were found with infor- mation concerning host species for these two long- horned beetles. The suitability of tree species as hosts was ranked as: very good host, good host, host, and rare/resistant based on information in the literature reviewed—for definitions used to classify hosts, see Table 1 (Yin and Lu 2005). In the publications stud- ied (Appendix 1; Appendix 2; Table 2), there was lack of consistent information on whether there is a complete life cycle of the beetles in the trees or if the adult beetles were simply feeding. When the infor- mation was imprecise regarding how a beetle attacks and feeds on a tree species, the species was ranked provisionally as a host. Information regarding the possibility for larva development by the beetles was included for all species (Appendix 1; Appendix 2). The information found in the review was then further analyzed in terms of aspects such as the origin of the findings [i.e., whether the informa- tion had been obtained through controlled green- house studies or studies in natural environments or plantations (Appendix 3)]. The geographical focus of the study was also included, as were any citations of the publication in the Scopus data- base. Host-related information within the studies was also analyzed to trace its origin (Appendix 3). RESULTS AND DISCUSSION Of the 35 papers reviewed, 29 contained informa- tion on host trees for ALB, while only 13 had cor- responding information for CLB. The total number of papers exceeded 35, since some studies covered both ALB and CLB and were therefore counted twice (Appendix 1; Appendix 2; Appendix 3; Table 2). In the compilation of host trees for ALB, 36 species were mentioned as a host to some degree, Very good host Good host Host Resistant or rarely affected ALB and CLB feeding and life cycle features Attracts longhorned beetles. Extensive feeding Moderate feeding. Can complete life cycle Limited feeding by adult beetles. Small number of eggs laid. Can escape attack if nearby trees are more susceptible No feeding activity by adult beetles; no eggs laid 145 while 31 genera were described as being at risk of attack—these genera obviously included many more than 36 species. The species described most frequently as a host to some degree was Acer platanoides, followed by A. saccharum and A. negundo. The genera described most compre- hensively as a good host for ALB were Populus spp., Salix spp., and Acer spp., followed by Betula spp., Ulmus spp., and Platanus spp. (Appendix 1). In the compilation of host trees for ALB, there were also 31 species and 16 genera that were described as resistant or rarely infested (Appendix 1). However, as can be seen from Appendix 1, there were some clear contradictions concerning which species and genera were susceptible. For example, some publications described a particular genus or species as a host to some degree, while oth- ers described them as resistant or rarely infested. Further, five publications described Tilia spp. as a host for ALB (Nowak et al. 2001; Ric et al. 2006; Hu et al. 2009; Jordbruksverket 2010; APHIS 2012), while two other publications stated that the genus of lime trees is rarely affected or even resistant (Haack et al. 1997; Raupp et al. 2006). This contra- diction regarding which species can be character- ized as hosts is even more pronounced in studies focusing on poplar trees (Populus spp.) and their susceptibility to ALB. Since there has been enor- mous use of poplar trees to counteract deserti- fication in northwestern China, several studies evaluate these poplar plantations and outbreaks of ALB (Lingafelter and Hoebeke 2002; Yin and Lu 2005; Yang 2005; Hu et al. 2009 and references therein). In these studies, it is obvious that not all poplar species are classified as a very good host for ALB, even if the genus is described as one of the Table 1. Division of host susceptibility into: very good host, good host, host, and rare/resistant. Host grade by adult beetles. Complete life cycle with population increase Impact on tree growth Dieback of whole tree crown or entire tree Dieback on some branches. Dieback of whole tree crown or entire tree if stressed Normal growth. Slight damage with recovery wounds Normal growth ©2014 International Society of Arboriculture
May 2014
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