Canadian Forest Service Publications
Wing wear and body size measurements of adult spruce budworms captured at light traps: inference on seasonal patterns related to reproduction. 2015. Rhainds, M. Applied Entomology and Zoology 50: 477-485.
Issued by: Atlantic Forestry Centre
Catalog ID: 39616
CFS Availability: PDF (download)
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Adult spruce budworms, Choristoneura fumiferana Clemens (Lepidoptera: Tortricidae), were captured at light traps in New Brunswick (NB) in 2012, Québec (QC) in 2013, and Newfoundland (NL) in 2014; population densities were low in NB–NL, and moderate in QC. Morphological parameters (wing score index, wing length, dry weight, residual fecundity) were estimated for thousands of adults. A very large number of budworms were captured during the night of 15–16 July 2013. The heavy weight and low proportion of eggs laid by these females suggest a synchronized, pulsed emergence of local adults rather than mass immigration. Variation in sex ratio and adult morphology suggest that populations were ‘closed’ at all locations (resident moths ⋙ immigrants), as indicated by an increasing proportion of females over time (protandrous emergence) and declining weight over time (reflective of the ageing of adults). The small size of adults in QC relative to NB–NL suggests that inverse-density dependent fecundity affects population dynamics early in the transition between endemic and epidemic phases. Wing wear provides a useful proxy for the age of adults: individuals with fresh wings (limited wear) were heavier than those with damaged wings, which likely reflects the metabolic costs of survival and (for females) the accruing proportion of eggs laid over time.
Plain Language Summary
A laboratory experiment was designed to evaluate factors affecting wing wear in spruce budworms; wing wear is equivalent to a fixed rate of wing damage that accrues with age and activity of adults. Adults with different wing wear condition, ranked from 1 (extremely damaged wings) and 10 (near mint wings at emergence), were pinned on a board and photographed to allow field assessments of wing wear among field collected adults.