Demographic and performance effects of alternative host use in a Neotropical treehopper (Hemiptera: Membracidae)

Abstract

The mechanisms which promote divergence in populations of phytophagous insects using alternative hosts depend on the characterization of hosts as different selective scenarios and the modeling of the demographic dynamics of the insect on those hosts. In the Bolivian Yungas forests, the treehopper Alchisme grossa (Hemiptera: Membracidae) utilizes two sympatric Solanaceae hosts, Brugmansia suaveolens and Solanum ursinum. On both hosts, females take care of nymphs during their development and adults use almost exclusively their natal host species. We characterized: 1) the performance of families (mother and nymphs) on both hosts, 2) maternal care across families and hosts, 3) biotic (herbivory, predators and parasites) and abiotic (temperature, relative humidity and luminosity) conditions across hosts and 4) demographic parameters of cohorts living under natural conditions on both hosts using matrix population modelling. The life cycle was longer on B. suaveolens than on S. ursinum. Microenvironmental abiotic and biotic traits differed between hosts. Nevertheless, performance did not differ between hosts and no differences between hosts were found in demographic parameters. None of the environmental variables explained the demographic parameters. Females performed maternal care with the same intensity on both hosts. Taken together with published data on the system, these results suggest that individuals of A. grossa in this study belong to a single population. Colonization of one of these hosts might be a recent event and evolutionary processes that promote ecological adaptation and hence demographic or performance differences have not yet become noticeable.