Effects of damage-induced and developmental changes of white birch (Betula papyrifera Marsh.) on populations of birch casebearer (Coleophora serratella L.) (Lepidoptera: Coleophoridae)

Piercey-Normore, Michele D. (1993) Effects of damage-induced and developmental changes of white birch (Betula papyrifera Marsh.) on populations of birch casebearer (Coleophora serratella L.) (Lepidoptera: Coleophoridae). Masters thesis, Memorial University of Newfoundland.

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Abstract

Insects feeding on a plant may induce changes within the leaves which affect success of insects subsequently feeding on that plant. The objective of this study was to demonstrate if birch casebearer feeding on birch leaves induced changes in the tree that would deter subsequent feeding by the same insect species. -- White birch trees were divided into four treatment groups of five trees each. Treatments consisted of birch leaves being severely damaged by insect feeding, lightly damaged by insect feeding, mechanically damaged with no insects present, and control with neither type of damage. Comparisons were made among treatment groups for 1) changes in the leaves, 2) population size of the birch casebearer at various times of the season, and 3) effects of damage-induced leaf changes on larval size. Damage-induced changes in the leaves were evident in nitrogen and phosphorus levels between 1991 and 1992, long-shoot length and number of buds, and bud development and leaf senescence. These changes were likely a result of nutrient depletion by insect feeding the previous year, reducing the tree's ability to compensate for losses. Population size of the birch casebearer between treatment groups changed very little throughout 1991 and 1992 suggesting that moths did not move far from the site of pupation. Positive correlation between nitrogen levels and egg density suggested that female moths might be able to distinguish between high and low leaf nitrogen levels, though this could occur within the same tree. Since headcapsule widths of Instar II larvae did not differ significantly between treatment groups, it appeared that damage-induced changes of white birch had no measurable effect on larval size. -- Leaf developmental changes, measured as water potential, water content, and fresh and dry leaf weights, were compared with seasonal changes in plant and insect life history stages. Egg hatch coincided with second leaf flush. Since eggs were laid on old leaves, it was suggested that Instar I larvae took advantage of nutrients being mobilized out of the older leaves and moving into younger leaves. -- The study showed no evidence for damage-induced leaf changes affecting success of the birch casebearer. However, there was speculation that the unusual life history pattern of the birch casebearer was adapted so that Instar I and II larvae could take advantage of mobilized leaf nutrients, lower water contents, and water potentials late in the season. Instar III and IV larvae, with faster growth, could take advantage of high leaf nutrients early in the season.

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