Canadian Forest Service Publications
Pheromone-based monitoring of spruce budworm (Lepidoptera: Tortricidae) larvae in relation to trap position. 2016. Rhainds, M.; Therrien, P.; Morneau, L. Journal of Economic Entomology 109(2): 717–723.
Issued by: Atlantic Forestry Centre
Catalog ID: 36816
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The local abundance of male spruce budworm, Choristoneura fumiferana (Clemens) (Lepidoptera: Tortricidae), was evaluated in the province of Quebec at 112 locations between 2002–2012 using pheromone-baited traps deployed on lower branches near the ground level (GL) or in the tree canopy (TC; three traps at GL and TC for each location); in addition, the presence of second instars (L2) was assessed at each location on three balsam fir branches. Numbers of moths captured at GL and TC were highly correlated, and the regression parameters did not vary between years. Consequently, estimates of L2 based on pheromone trap catches are precise independent of trap location, and deploying traps at ground level (rather than in the tree canopy) does not come with a loss of accuracy in L2 assessments. Relationships between moths (x) and L2 (y) exhibited strong nonlinearity and were most adequately described by exponential functions of the form: ln (y +1) = [ß0 = ß1 x kln (x)]. A conservative threshold of 100 males per trap at GL (corresponding to one L2 per branch) may be used to guide forest managers in the transition from endemic to epidemic populations. Relationships between L2 and moths are likely influenced by the number of traps per site; hence, the tentative threshold above is only valid for jurisdictions relying on three traps per site. Considering the economic importance and rising populations of spruce budworm, rigorous quality control programs must be implemented promptly to ensure a steady supply of standardized pheromone lures across years.
Plain Language Summary
With the steadily growing outbreak of spruce budworms, it is becoming increasingly important to obtain accurate estimates of population density. The current study compared captures of moths at pheromone-baited traps versus densities of L2 per branch at hundreds of sites between 2002 and 2012 in the province of Quebec. Traps were deployed on branches either in the upper canopy or at ground level (2 m high). The position of traps did not affect the accuracy of larval density estimates, thus deploying traps in lower branches reduce monitoring effort with no cost in terms of sampling precision. Forest managers should become familiar with the non-linear functions characterizing the relationships between numbers of males (x) and larvae (y) [y ~ k (power x)]. Because the data in Quebec are more extensive than for any other province, it is recommended that all jurisdictions revise their pheromone monitoring program by deploying three traps at each location (rather than one as is currently the norm).