Abstract
White spruce (Picea glauca (Moench) Voss) trees that are resistant or susceptible to spruce budworm (Choristoneura fumiferana (Clem.)) attack were identified in a southern Quebec plantation. Due to high mortality-induced selective pressures imposed by resistant trees on spruce budworm larvae, insects that survive on resistant trees exhibited greater biological performance than those on susceptible trees. We tested the hypothesis that this better biological performance is maintained across generations when progeny were subjected to nutritional stress. We collected pupae from resistant and susceptible trees (phenotype). Adults were reared under controlled laboratory conditions. Progeny were subsequently reared on two types of artificial diet (high vs. low quality). Low quality diet simulated food quality deterioration during outbreak conditions. Results confirmed that surviving insects collected from resistant trees have better performance than those from susceptible trees. Offspring performance (pupal mass, developmental time) was affected only by diet quality. These results suggest that adaptive advantages that would be acquired from parents fed on resistant trees are lost when progeny are exposed to nutritionally-imbalanced food, but the effects persist when larvae are fed a balanced diet. Offspring mortality, fecundity and fertility were positively influenced by parental origin (tree phenotype).
Highlights
Defense mechanisms in plants that confer resistance to herbivory [1] are closely implicated in the coevolution between insects and plants [2,3]
Female and male individuals that originated from resistant white spruce exhibited higher pupal mass, but lower fecundity than those coming from susceptible trees
Larvae of both sexes that were reared on the high quality diet had higher pupal masses (Figure 1e), shorter developmental times (Figure 1f) and lower mortality (Figure 1a) than those that were reared on the low quality diet
Summary
Defense mechanisms in plants that confer resistance to herbivory [1] are closely implicated in the coevolution between insects and plants [2,3]. These mechanisms represent important selection pressures that negatively affect insect performance variables, such as survival, fecundity, pupal mass and growth rate [4]. Host resistance may differ among tree species, among conspecifics and even within individual trees. This phenomenon can be illustrated with the relationship between spruce budworm and its hosts. Its main host tree is balsam fir, Abies balsamea (L.) Miller, followed by white spruce, Picea glauca (Moench) Voss, black spruce, P. mariana (Mill.) BSP, and red spruce, P. rubens
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