ABSTRACT
Phenotypic plasticity as defined by Pigliucci (2001) is, "the property of a given genotype to produce different phenotypes in response to distinct environmental conditions" implying a distinct predictable impact of certain environmental conditions rather than random noise. The non-genetic environmental induction of host plant preference (whether an increased 'specificity' or a change in 'rank order'; Courtney and Kibota 1990) is a classical example of phenotypic plasticity (Agrawal 2001). Phenotypic plasticity has been observed at least since the study of the genetic control of traits was begun in the early 20th century. However, the factors causing the differential expression of genotypes have remained a challenge in most systems. A key problem is the difficulty of separating the various environmental factors organisms encounter in nature from the genetic variability present in populations (Mousseau and Roff 1987, Mousseau et al. 2000). In some situations, environmentally induced (i.e. plastic) traits may even become fixed (genetically invariant) in populations via selection for stable expression of the trait under new conditions so that it no longer requires the original environmental stimulus (i.e. 'genetic assimilation'; Pigliucci and Murren 2003). Further complications arise when attempting to identify the environmental factors inducing the differential expression, and the mechanism(s) that facilitate this induction.
