Relationship between balsam fir sawfly density and defoliation in balsam fir

Linear and non-linear impacts of a non-native plant invasion on soil microbial community structure and function

“…Empirical evidence to support this body of theory is limited, but research examining the relationship between density and impact of crop pest species in agricultural and forestry systems has shown both linear (Poché et al 1982;Parsons et al 2005) and nonlinear relationships (Liebhold et al 1993;Nava-Camberos et al 2001;Brown et al 2007). Together, this body of ecological theory and the empirical results from agricultural and ecological studies suggest that per capita impacts are not constant, and that the utility of this framework for assessing impacts of early-stage invasion is severely limited.…”

Influence of pre-commercial thinning of balsam fir on defoliation by the balsam fir sawfly

“…Although we only estimated egg densities in year 2000, and thus did not necessarily measure the average egg densities in a stand during all stages of an outbreak, our results are consistent with those of a longer term study that also reported that densities of N. abietis were higher in thinned than unthinned balsam fir stands in the early stage of outbreaks (Moreau, 2004). It has been previously shown that the density of eggs of N. abietis is strongly related to subsequent defoliation (Parsons et al, 2005).…”

“…Cumulative percent defoliation was visually estimated on each age-class of foliage from each second-order branch (Piene, 1989). Cumulative defoliation estimates did not include current-year foliage, which is rarely eaten by the sawfly (Parsons et al, 2003(Parsons et al, , 2005 and were corrected by subtracting natural needle fall, which was estimated from undefoliated trees in Nova Scotia and Newfoundland.…”

Relationships between yellowheaded spruce sawfly, Pikonema alaskensis, density and defoliation on juvenile black spruce

“…These relationships can be used to establish an economic injury level (Pedigo et al, 1986), and thereby facilitate decision-making regarding the application of suppression tactics (Binns and Nyrop, 1992). In response to increasing pressure to fulfill the conflicting economic and ecological demands of effective suppression with minimal environmental effects, the establishment of densitydefoliation relationships has become increasingly prevalent in forest pest management (Waters and Stark, 1980;Gansner et al, 1985;Lysyk, 1990;Alfaro, 1991;Williams et al, 1991;Carroll and Quiring, 1993;Liebhold et al, 1993;Fang and Hart, 2000;Nealis and Turnquist, 2003;Parsons et al, 2005).…”

“…Similarly, responses of host-plants to herbivory can be highly variable due to variations in site quality (Morse and Kulman, 1986), defoliation intensity (Kulman, 1971;Piene and Little, 1990) or history (Vanderklein and Reich, 1999), and/or the location of plant tissue consumed (Honkanen and Haukioja, 1994). A basic understanding of an insect's foraging behavior (Carroll and Quiring, 1993;Parsons et al, 2005) and/or the capacity of its host to compensate for the injury inflicted (Trumble et al, 1993) are needed to establish robust relationships relating current pest density to future host-plant damage.…”