Effect of fertilization of balsam fir trees on spruce budworm nutrition and development
Spruce budworm (Choristoneurafumiferana Clem.) larvae were reared on field-grown balsam fir (Abiesbalsamea (L.) Mill.) trees variously treated with nitrogen, potassium, and phosphorous fertilizers. Treatment with high nitrogen had a significant effect on terminal shoot growth, the caloric value, the concentrations of total sugar, starch, crude fat, nitrogen, chlorophyll, and moisture, and the calories per milligram protein in maturing current-year needles, the budworm's food. Concomitantly, high nitrogen increased male and female pupal weight. Ammonium acetate had less effect than urea or calcium nitrate on both tree and budworm responses, and low urea had less effect than high urea. High potassium, particularly in the presence of low urea, negatively affected some tree and budworm responses. Larval survival was increased only by calcium nitrate application. Of all the foliar parameters, the calories per milligram protein and the nitrogen concentration were best correlated with pupal weight. Female pupal weight was positively correlated with number of F1 larvae per female moth. The results support the hypothesis that food quality can significantly affect budworm population dynamics.