Spruce budworm growth, development and food utilization on young and old balsam fir trees

Abstract

Laboratory rearing of spruce budworm, Choristoneura fumiferana, in conjunction with field rearing, gravimetric analyses, a transfer experiment, and foliage chemical analyses at six dates during the period of budworm feeding activity indicated that the age of balsam fir, Abies balsamea, trees (70-year-old mature trees or 30-year-old juvenile trees) affected tree suitability for the spruce budworm via the chemical profile of the foliage. Insects reared on old trees had greater survival and pupal weight, shorter development times, and caused more defoliation than those reared on young trees. Young trees were more suitable for the development of young larvae (instars 2-5), while old trees were more suitable for the development of older, sixth-instar larvae. These results were confirmed by the laboratory transfer experiment. Young larvae fed foliage from young trees had higher relative growth rates (RGR), digestibility (AD), and efficiency of conversion of ingested foliage (ECI) than those fed foliage from old trees. These differences appeared to be related to the high N:tannins ratio, and the high contents of P present in young trees during the development of the young larvae. Old larvae fed foliage from old trees had higher relative growth rates, relative consumption rates (RCR), and digestibility of the foliage than those fed foliage from young trees. The high digestibility of the foliage of old trees was compensated for by a lower efficiency of conversion of digested food (ECD), which in turn resulted in no significant effect of tree age on the efficiency of conversion of ingested foliage by old larvae. The low relative consumption rate of old larvae fed foliage from young trees appeared to be related to the low N:tannins ratio, and the high contents of bornyl acetate, terpinolene, and °-3-carene present in young trees during the budworm sixth instar. Variations in these compounds in relation to tree age may serve as mechanisms of balsam fir resistance to spruce budworm by reducing the feeding rate of sixth instar larvae.

One and two years impact of commercial thinning on spruce budworm feeding ecology and host tree foliage production and chemistry

“…The dry weight of frass produced in each rearing sleeve cage was recorded, pupae were weighed, and moth emergence was monitored every half hour, 24 h a day. Results from a study on spruce budworm food utilization that combined laboratory and field rearing experiments indicated that the rearing technique used in the present study gives an accurate estimate of h s s production (Bauce et al 1994). On each 55-cm-long branch, the total amount of c m t -y e a r foliage produced (AFP), the amount of current-year foliage destroyed by the larvae (AFD) and the amount of residual current-year foliage remaining on each branch after budworm defoliation (ARF) were determined using Bauce et al (1994) methodology by (1) determining, for each tree, using two north-northwest facing midcrown uninfested branches, the number of needles per cm of current-year twigs, and the mean dry weight of a needle, (2) measuring on the budworm infested branches the total length of current-year twigs, (3) measuring the length of defoliated twigs, (4) converting cm of twigs in number of needles, and (5) converting number of needles in weight of foliage.…”

“…An additional 100 mg of dried foliage was extracted three times with 70% acetone containing 0.1% ascorbic acid (Dement and Mooney 1974;Wisdom et al 1987) and the resulting liquid phase was analyzed for total tannins using the technique of radial diffision in agar medium with BSA protein (Hagerman 1987), and for total phenolics using the Folin-Denis reaction (Swain and Hillis 1959). Two additional subsamples of fresh twigs were collected, placed in crimped seal vials and kept at-20°C until needles were analyzed for monoterpene contents using the methodology descri'oed in Bauce et al (1994). The experiment was repeated using different trees in 1993.…”

“…Compared to break because the stress caused by the treatment to the a s may trees with low ARF, trees with high ARF should be less w lrender them more vulnerable to the insect. The term ''v~lner-nerable to spruce budworm defoliation because they have ability" refers to the conditions which afiFmt the degree of dammore foliage to produce photosyntates (Bauce et al 1994). age sustained by trees once attacked (Witter 1985).…”

Croissance des branches et des tiges d'épinette noire :

“…Donc l'ensoleillement aurait une influence sur l'invasion d'une branche par la TBE. Mais une trop forte concentration de monoterpènes agiraient négativement sur la croissance des larves du 6 ème stade (Bauce et al, 1994). Aucune littérature n'a encore traité en détail, l'effet des monoterpènes sur la croissance des larves des premiers stades.…”

Effet d'une épidémie de la tordeuse des bourgeons de l'épinette sur la croissance de la tige et le développement racinaire des semis de sapin dans des sapinières boréales /

“…Malgré que les mécanismes n'en soient pas vraiment élucidés, la survie des semis de sapin sous le couvert forestier est meilleure que celle des sapins dominants (MacLean et Piene, 1994;Reams, 1988;Miller, 1977). Bauce et al (1994) ont trouvé que des variations de la qualité du feuillage des sapins reliées à l'âge de ceux-ci, peuvent expliquer la performance accrue des larves de la tordeuse se nourrissant sur les sapins de 70 ans comparativement aux sapins de 30 ans.…”