Resource choice in Cuscuta europaea.

Individual stems with growing tips of dodder (Cuscuta europaea) were transplanted onto host plants (hawthorn) of varying nutritional status. The parasite was more likely to coil on ("accept") hosts of high nutritional status and grow away from ("reject") hosts of poor quality. Dodder exhibits this acceptance/rejection response before taking up any food from the host, so it is possible to dissociate active choice from the passive effects of growth and mortality. Probability of acceptance is gauged to expected reward.