Neotropical rolled-leaf beetles (Chrysomelidae: Hispinae: tribes Cephaloleiini and Arescini) are specialist herbivores that live and feed in immature rolled leaves of their host plants (Order Zingiberales). As a first step towards understanding the evolution of this ancient plant-insect interaction, we investigated how leaf characteristics influence the rate of colonization of Pleiostachya pruinosa (Zingiberales: Marantaceae) by its specialist rolled-leaf beetle Cephaloleia fenestrata. The leaves normally colonized by the beetles are both young (newly emerged) and in a rolled configuration. Leaf configuration is correlated with leaf age, since leaves unroll as they mature, so we used experimental manipulations to ask whether configuration and age are independently important for colonization. We manipulated the configuration of both mature and young P. pruinosa leaves so that they were either rolled tightly to a small diameter, rolled more loosely to a larger diameter, or completely unrolled. Leaves were checked after 24 hours for colonization by C. fenestrata.
Results/Conclusions
Leaf configuration and leaf age both significantly influenced the probability of leaf colonization. There was essentially no colonization on mature leaves (only 1 out of 168 mature leaves were colonized), whether rolled or not. On young leaves, beetle colonization was highly dependent on leaf configuration. Rate of colonization was highest on tightly rolled leaves (50% of 82 leaves colonized), less on loosely rolled leaves (18.1% of 55 leaves), and absent on experimentally unrolled leaves (0 of 56 leaves). This pattern of colonization indicates that C. fenestrata discriminates between leaves on the basis of both leaf age and physical configuration. There are several hypotheses to explain C. fenestrata’s preference for leaves that are both tightly rolled and young, including selection on the beetles to (1) occupy enemy-free space, (2) find the highest quality food resources, and (3) optimize the ratio of time spent in leaf rolls relative to time spent dispersing.