Colonization by herbivores of Heliconia spp. plants (Zingiberales: Heliconiaceae)

The leaf-top herbivore guild of Heliconia spp. is a particularly good subject for the examination of host colonization because individuals may be monitored easily for extended periods of time. Studies of the guild on H. imbricata in Costa Rica and on H. latispatha in Ecuador reveal substantial variation in the rates of colonization among plants. The variation is explained best by the insects' response to environmental conditions, in particular, light and moisture. THE STIMULI PROMOTING HOST CHOICE by herbivorous insects are relatively unknown (e.g., Futuyma and Gould 1979; Fox and Morrow 1981; Rausher 1981; Dethier 1982). Recent attempts to correlate patterns of herbivore choice with taxonomic and ecological groupings of plants are indecisive (Futyuma and Gould 1979, Holloway and Hebert 1979, Fox and Morrow 1981). Most baffling is the variation in herbivore accrual among individual plants within a population: why should herbivore individuals be clumped on certain plants? Suggestions advanced for intra-specific herbivore choice include plant secondary chemistry (Cooper-Driver et al. 1977), plant nutrient content (Myers and Post 1981), herbivore aggregation pheromones (Howe et al. 1976), and environmental conditions (Maiorana 1981). Colonization of the tropical rain forest monocots Heliconia imbricata (0. Ktze.) Baker and H. latispatha Benth. by some herbivorous insects provides insight into this problem. THE LEAF-TOP HERBIVORE GUILD The herbivores that feed upon surfaces of leaves of Heliconia spp. live beneath accumulated debris, and feed upon the epidermis of the host plants' large, horizontallyheld leaves. Detritus of leaves and of other plant parts from trees above Heliconia plants retains moisture even when the uncovered portions of leaves dry between rains. Debris forms patches of habitat for the insects. Both larvae and adults of the insects disperse among the patches of debris. The most common herbivores in leaf-top debris on H. imbricata in Costa Rica are larvae and adults of Cheirispa dorsata Baly (Coleoptera: Chrysomelidae), larvae of Cephaloleia consanguinea Baly (Coleoptera: Chrysomelidae), and the larvae of an unidentified lepidoteran (Fig. 1). Searches of debris upon large numbers of other plant species near colonies of the leaftop guild at La Selva have revealed either species different from those of H. imbricata or no arthropods at all. Other Heliconia species of similar size often accommodate one or two of the species of this guild, but C. consanguinea is specific to H. imbricata (Strong 1977a, b; 1982). At La Selva, H. imbricata is by far the most abundant Heliconia species. Likewise, H. latispatha is the most common Heliconia species at Rio Palenque, Ecuador. There, I have found the leaf-top herbivore guild to include the larvae of two unidentified chrysomelid beetles, one very similar in size and appearance to C. consanguinea, and larvae of an unidentified lepidopteran.