PITCHER DIMORPHISM, PREY COMPOSITION AND THE MECHANISMS OF PREY ATTRACTION IN THE PITCHER PLANT NEPENTHES RAFFLESIANA IN BORNEO

1 The pitcher plant Nepenthes rafflesiana Jack produces dimorphic pitc her types. Upper pitchers catch more flying prey than lower pitchers. The most important single prey group in both pitcher forms was Formici dae. 2 Both pitcher forms possess ultraviolet (UV) patterns which were associated with the site of the major nectaries, causing it to stand out in contrast to the adjacent area. Manipulation of these patterns i n upper pitchers confirmed their role in the attraction of prey. 3 Upp er pitchers produce a fragrance which is attractive to flying prey. Th e combination of visual and olfactory cues accounted for the greater p rey attraction of upper over lower pitchers. This is confirmed by the pitchers of N. rafflesiana var. elongata, which possess neither UV pat terns nor fragrance, and catch significantly less prey than the typica l form. 4 Lower pitchers resting at ground level, where densities of p otential invertebrate prey are highest, are less than optimally attrac tive. This may reduce the amount of prey caught, thus preventing overl oading and consequent putrefaction of the contents, and death of the p itchers.