Summary: Plant genotype and induced responses affect resistance
to herbivores on evening primrose (Oenothera biennis)
ROSANNA J. MCGUIRE and MARC T. J. JOHNSON Department of Botany, University
of Toronto, Canada
Abstract. 1. Although both genotype and induced responses affect a plant's
resistance to herbivores, little is known about their relative and interactive effects.
This study examined how plant genotype of a native plant (Oenothera biennis) and
induced plant responses to herbivory affect resistance to, and interactions among,
2. In a field experiment, genetic and environmental variation among habitats
led to variation in the amount of early season damage and plant quality. The
pattern of variation in early season infestation by spittlebugs (Philaenus spumar-
ius, a piercingsucking herbivore) negatively correlated with oviposition prefer-
ence by a later feeding specialist weevil (Tyloderma foveolatum, a leaf-chewer).
3. To determine if plant genotype and induced responses to herbivory might be
responsible for these field patterns, we performed no-choice and choice bioassays
using four genotypes of O. biennis that varied in resistance. Plants were induced
by either spittlebugs or weevils and assays measured the responses of the same
specialist weevil as well as a generalist caterpillar (Spodoptera exigua).
4. Resistance to adult weevils was largely unaffected by plant genotype, while