38 Fettig et al.: Sampling of Forest and Shade Tree Insects A REVIEW OF SAMPLING PROCEDURES AVAILABLE FOR IPM DECISION-MAKING OF FOREST AND SHADE TREE INSECTS IN NORTH AMERICA By Christopher J. Fettig1 , Jeffrey G. Fidgen2 , and Scott M. Salom3 Abstract. Integrated Pest Management (IPM) programs attempt to reduce insect associated losses to acceptable levels using multiple techniques that are effective, economically viable, and ecologically compatible. Sampling is the cornerstone of any IPM program, and significant effort has been devoted to the develop- ment, theory, and application of sampling methods. Relatively few IPM programs exist for managing forest and shade tree pests despite the availability of sampling procedures that are potentially useful for control decision-making. The majority of these sampling procedures are published on defoliating insects (58% of all publications). The most commonly referenced defoliators are the gypsy moth, Lymantria dispar (L.); Douglas-fir tussock moth, Orgyia pseudotsugata (McDunnough); spruce budworm, Choristoneura fumiferana (Clemens); and western spruce budworm, C. occidentalis Freeman. These four species alone account for 35% of all sampling publications relevant to IPM programs. The second largest group is bud, shoot, and root insects (16%) followed closely by wood- and bark-boring insects (11%). The piercing–sucking feeding group (10%) and seed and cone insects (5%) have relatively few sampling procedures available. Ninety-two percent of the species represented are predominately forest pests, with the order Lepidoptera and family Tortricidae most commonly reported. A significant opportunity exists for developing similar tools to aid in control decision-making for a large number of other pests. Current trends suggest that efforts should concentrate on species important to the urban forest and intensively managed forest plantations. Key Words. Sampling techniques; sampling programs; sequential sampling; action thresholds; forest insects; shade tree insects; urban forestry. The development of sampling programs for arthropod pests is an extensive area of research (Morris 1955; Strickland 1961; Southwood 1978; Coulson and Witter 1984; Billings 1988; Barbosa and Wagner 1989; Dent 1991; Kuno 1991; Binns and Nyrop 1992; Pedigo and Buntin 1994; Sidebottom 1995; Fettig et al. 2001) and consists of two distinct components: the sampling technique and sampling program (Pedigo 1989). An effective sampling technique, such as in situ counts or trapping, must first be developed to facilitate collection of data during each sample. The sam- pling program describes procedures for deploying the sampling technique temporally and spatially (Pedigo 1989, ©2005 International Society of Arboriculture 1994). For example, a typical sampling program will define the sample unit, the appropriate insect stage to sample, the number of samples to be collected, the timing of each sample, and the pattern of sampling (i.e., random or systematic) (Southwood 1978; Pedigo 1989, 1994; Royama 1992; Fox et al. 1997). Today, decision support systems are commonly used to integrate sampling estimates, action thresholds, and geographical information systems into useful area-based platforms (Power et al. 2001). Action or economic thresholds indicate when manage- ment actions should commence (Pedigo et al. 1986; Pedigo 1989) and can result in substantial reductions in insecticide use at a considerable cost savings (Coffelt and Schultz 1990; Dent 1991; Binns and Nyrop 1992; Fox et al. 1997). Thresholds are often based on relationships between pest density and host impacts (Raupp et al. 1992; Rieske and Raffa 1993; Liebhold et al. 1994), such as aesthetics (Buhyoff et al. 1982; Coffelt and Schultz 1990), loss of growth or vigor (Fox et al. 1997), and economics (Pedigo et al. 1986; Rawat et al. 1987; Fox et al. 1997). Sequential and binomial sampling plans are extremely useful for decision-making purposes (Waters 1955; Binns and Nyrop 1992). In entomology, sequential sampling plans are based on dispersion patterns and action thresholds, which facilitate placement of populations into crude categories (e.g., endemic and epidemic) with an economy of samples. When pest populations are either very low or very high, sequential sampling plans require about half the effort of plans based on fixed sample sizes (Waters 1955; Fowler and Lynch 1987; Binns and Bostanian 1990; Brewer et al. 1994; Fettig et al. 2001). Binomial sampling programs relate a variable that is easy to measure, such as the proportion of sampling units that are infested, with one that is more difficult to obtain, such as absolute density (Waters 1955; Brewer et al. 1994; Nyrop and Binns 1992). Many variations of the two sampling plans exist (Fowler and Lynch 1987; Pedigo 1989, 1994; Legg et al. 1994; Fettig et al. 2001). Much of the forest and shade tree sampling literature is difficult to find and interpret and is, therefore, inaccessible to most resource managers. In 2001, we compiled all sampling techniques on forest pests and developed an unambiguous, comprehensive database useful to resource
January 2005
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