Journal of Arboriculture 31(1): January 2005 43 Tortricidae (Lepidoptera) was the most common family among species reported by Fettig et al. (2001). This family was unique in that representatives were present in three feeding groups (Table 2). Thirty percent of all publications included sampling methods or programs relevant to tortricid species. Lymantriidae (Lepidoptera) was a distant second and accounted for 20% of publications. Only two species, L. dispar and O. pseudotsugata, were represented. However, both are notable defoliators that receive near-continuous research attention in both urban and forested environments. RELATIVE ABUNDANCE OF HOSTS Eighty-one percent of summaries referenced a conifer as the primary host. Pinus (30%), Picea (19%), and Abies (15%) were the most commonly reported genera. Four of the most commonly referenced species are exclusively pests of conifers, including O. pseudotsugata, C. fumiferana, C. occidentalis, and D. frontalis (Table 2). Although L. dispar is known to feed on conifers, this phenomenon is rare and often occurs only in the absence of preferred hosts (Coulson and Witter 1984). Among hardwoods, the most common hosts were Quercus spp. RELATIVE ABUNDANCE OF FOREST AND SHADE TREE PESTS Ninety-two percent of the species reported were predomi- nately forest pests (Table 2). The substantial lack of publica- tions on shade tree insects is surprising. Shade trees, such as those located in residential, recreational, or administrative sites, are particularly susceptible to insect attack as a result of increased amounts of stress associated with drought, soil compaction, mechanical injury, or vandalism. Additionally, the effectiveness of biological controls is reduced in these systems (Coulson and Witter 1984). The value of these trees is also much higher than their forest counterparts (McPherson et al. 1999). For example, Nowak et al. (2001) estimated the maximum potential impact of the Asian longhorned beetle, Anoplophora glabripennis (Coleoptera: Cerambycidae), to urban forests at US$669 billion. Individual estimates ranged from US$72 million to US$2.3 billion per city. The urban forest is a large and currently expanding area that provides numerous benefits to its residents (Dwyer et al. 2003). The need for sampling programs of shade tree insects is paramount. The system naturally lends itself to the develop- ment and implementation of such tools because of the “market values” of the crop, the increased susceptibility of the hosts, and their relatively isolated distribution within the landscape. Unfortunately, at present, such programs are lacking, and communities are most frequently forced to rely on crude judgments for control decision-making. A notable exception is the recent development and implementation of citywide monitoring programs for the elm leaf beetle, Xanthogaleruca luteola (Müller), in California (Lawson and Dahlsten 2003). This program resulted in a dramatic reduction in insecticide use at a considerable cost saving (Lawson and Dahlsten 2003) and is a prime example of the importance of developing such tools and the benefits that can be realized by their application to the urban forest. RELATIVE ABUNDANCE OF SEQUENTIAL OR BINOMIAL SAMPLING PLANS AND ACTION THRESHOLDS In our analysis, we tallied the total number of sequential sampling plans, action thresholds, and density–damage relationships (that did not explicitly specify an action threshold) in each feeding group because of their impor- tance in control decision-making. In several publications, an action threshold (or economic impact level, EIP) was not specified. In these cases, we used the high-density estimates as an action threshold when available. Sequential and Binomial Sampling Plans Sequential sampling plans were reported for 30%, 55%, 27%, 75%, and 50% of the species in each feeding group, respectively (Table 2). More than 45% of all species have sequential sampling plans available (Table 2). Of species classified as at least moderately important in the United States, 26% have sequential sampling plans. Unfortunately, to our knowledge, few receive much attention by practitio- ners. Of the five species for which the majority of sampling programs have been developed, only D. frontalis is without a sequential sampling plan (Table 2). Sampling for this forest pest has focused on area-wide trapping surveys to forecast changes in population trends (Billings 1988). It has been difficult to develop a useful and easy-to-implement sampling procedure for D. frontalis, and other bark beetles because they remain hidden beneath the bark for most of the life cycle (Coulson and Witter 1984). Action Thresholds and Other Density–Damage Relationships Action thresholds are available for 42% of the species reported and for all seed and cone insects referenced. Insects that infest reproductive structures are often consid- ered among the most significant forest pests (Coulson and Witter 1984). Prior to the early 1960s, these species were of relatively little importance to forestry. With the advent of extensive seed orchards to produce genetically superior seeds, interests in managing insect associated losses in- creased. To that end, all sampling publications were pub- lished after 1980. Action thresholds were provided for 55% of piercing–sucking pests (Table 2). These pests mainly degrade the aesthetic quality of ornamental and Christmas trees. Enumerative sampling is often required for control decision-making in place of binomial or sequential sampling plans (Sidebottom 1995). A density–damage relationship is available for an additional 12% of the species reported by ©2005 International Society of Arboriculture
January 2005
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