Canadian Forest Service Publications

A sampling unit for estimating gall densities of Paradiplosis tumifex (Diptera: Cecidomyiidae) in Christmas tree stands. 2013. Carleton, R.D.; Silk, P.J.; Eveleigh, E.S.; Heard, S.B.; Dickie, C. The Canadian Entomologist 145: 343–349. doi:10.4039/tce.2012.104, 00: 1-7.

Year: 2013

Issued by: Atlantic Forestry Centre

Catalog ID: 34794

Language: English

Availability: PDF (request by e-mail)

Available from the Journal's Web site.
DOI: 10.4039/tce.2012.104

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We used field surveys in central New Brunswick, Canada to establish efficient sampling procedures for evaluating densities of balsam gall midge, Paradiplosis tumifex Gagné (Diptera: Cecidomyiidae), and its associated damage in balsam fir, Abies balsamea (Linnaeus) Miller, Christmas trees. Infestation was greater in larger trees than smaller trees and in mid-crown and upper-crown branches than in the lower crown. However, the relationship between gallmaker infestation and site, height class, and crown level was highly complex and may involve covariation of shoot length with height class and crown level. As a result, patterns in infestation did not lend themselves to simple interpretation. This complexity highlights the need to find sampling units that provide simpler but reasonably accurate predictors of gallmaker impact at the whole-tree scale. We identified such a sampling unit: gallmaker density in first-order current-year shoots of a mid-crown branch explained 81% of the variance in total infestation among trees.

Plain Language Summary

Insects often damage host plants in predictable patterns that are typically driven by some underlying factor or combination of factors (for example, quality of resource, predator avoidance, etc.) These patterns, if accurately identified, allow us to develop simple sampling units to predict the insect damage at the plant level. A simple sampling unit allows for a more rapid assessment of insect damage at a larger scale, thereby improving decision-making strategies for pest management. We identified this link between the patterns of gall distribution by the balsam gall midge in young, balsam fir stands in central New Brunswick. Our results indicate that one south-facing, mid-crown terminal shoot cluster will predict gall densities on a whole tree. This sampling unit will be used in future research to develop a sampling plan for balsam gall midge in young, balsam fir stands.