The semi-aquatic grasshopper Cornops aquaticum (Bruner, 1906) is native to South America, with a distribution from the Argentinian pampas to the Gulf of Mexico, and is currently being proposed as a biological control agent for the invasive water hyacinth (Eichhornia crassipes) in South Africa. This study reports results of a neutral molecular marker (microsatellites) study on C. aquaticum within its native range. The data were analysed for levels of diversity and structure within/between South American populations, and correlations between host plant, geography and environmental/climatic variables were investigated. We found no evidence to support associations between host plant use and microsatellite genotypes (hypothesis 1). High levels of gene flow and weak genetic clustering of populations indicate a lack of differentiation, therefore an interaction between climate and local genotype (hypothesis 2) seems unlikely. Our results suggest that C. aquaticum may not have ''tightly'' coevolved with its host Eichhornia spp. (Pontederiaceae) as originally thought, and that instar variation might be due to the effect of local climate on phenotype (hypothesis 3) or possibly a locally adaptive trait.

The semiaquatic grasshopper Cornops aquaticum is native to South America, with a distribution as far south as the Argentinean pampas and as far north as the Gulf of Mexico. This grasshopper is being proposed as a form of biological control agent for the invasive aquatic macrophyte (Eichhornia crassipes) in South Africa. The results of a molecular study (six microsatellite loci) conducted on 11 C. aquaticum populations is presented. Unlike in contiguous mainland South American populations, we found genetic diversity to be lowest in a South African quarantine population, with reduced values in two other isolated populations from South America. In addition, F-st/R-st/analysis of molecular variance and Bayesian cluster analysis suggested high levels of connectivity between mainland populations. The implications of these findings and their relationship to those of a recent morphological study suggest that the suitability of C. aquaticum as a form of biocontrol might be unpredictable at best