Phytochemical basis of learning inRhagoletis pomonella and other herbivorous insects.

Examples of phytochemically-based learning of host preference in herbivorous insects are reviewed in the context of traditionally important issues: the number and kinds of chemicals involved; which sensory modalities are affected; whether peripheral or central nervous processing is altered; and whether learning is associative or not. A fifth issue addressed here- whether experience enhances a feeding or ovipositing insect's propensity to accept familiar chemical stimuli or to reject novel chemical stimuli-has been ignored in previous studies. Following the review, evidence is presented indicating that female apple maggot flies (Ragoletis pomonella) learn to reject both novel physical and novel chemical stimuli.