Dispersion patterns of eggs and larvae of the weevilNeochetina eichhorniaeWarner within waterhyacinth shoots were examined in two field studies. In whole-plant dissections, eggs were rarely found in the youngest, uppermost leaves but were common in mature leaves. Late instars occurred more frequently in older leaves, usually concentrated in the basal portion of the petiole. As instar increased, increasing proportions occurred within the stem (rhizome). In a second study, plants were first grown in small pools for varying durations, then transplanted to a field site. Leaf age accounted for 83% of among age-class variation in average number of eggs per leaf, and more eggs were found in older leaves. Time in the field accounted for 89% of variation in average number of larvae per leaf when standardized to percentages of the total found at each harvest. Dispersion of eggs seemed to be influenced by leaf age but dispersion of larvae was strongly influenced by exposure duration. Selection of leaves for oviposition by female weevils may be based upon distribution of secondary metabolic compounds or nutrients, or both. Leaf senescense and ultimate sloughing of the leaf from the shoot could be a significant source of mortality to eggs and possibly larvae. Ontogeny and leaf dynamics are important driving forces in dispersion of the relatively immobile insects within waterhyacinth shoots. Third instars, however, seem able to move easily within the shoot and are less affected by leaf dynamics. Movement by larvae to petiole bases probably maximizes their chances of staying with the shoot if the leaf detaches.