Canadian Forest Service Publications
Increased mortality or the Swaine jack pine sawfly, and foliar nitrogen concentrations after urea fertilization. 1973. Smirnoff, W.A.; Bernier, B. Canadian Journal of Forest Research 3(1): 112-121.
Available from: Laurentian Forestry Centre
Catalog ID: 16079
Mortality of the Swaine jack-pine sawfly larvae (Neodiprion swainei Midd.) introduced as colonies on jack-pine (Pinus banksiana Lamb.) foliage was measured in untreated and urea-traited plots of natural forest. Following applications of urea (400 kg N/ha) repeated in two successive years, natural mortality increased from 40 to 70% after 4 weeks, from 33 to 51% after 6 weeks, and from 18 to 36% after 4 weeks for larvae introduced as 1st instar, 2nd instar, and 3rd instar, respectively. This was accompanied by a marked reduction in foliage consumption as revealed by direct measurements or by the weight of frass collected. With 3rd-instar larvae sprayed with a suspension of the virus Borrelinavirus swainei (Smirnoff), viral infection developed much more rapidly in larvae placed on fertilized trees, mortality reaching 100%, double that measured on unfertilized trees. Single applications of urea at lower rates (100 and 200 kg N/ha) revealed a trend of increasing mortality for both unsprayed and virus-sprayed larvae with increasing urea application rate and increasing nitrogen concentration in the needles. Changes in the nitrogenous composition of needle tissue are considered an important factor in the increased larval mortality.
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