How safe is the grasshopper Cornops aquaticum for release on water hyacinth in South Africa?
The grasshopper Cornops aquaticum is currently being considered as a natural enemy for water hyacinth (Eichhornia crassipes) in South Africa. Both adults and nymphs are very damaging to water hyacinth plants. The laboratory host range was determined through nymphal and adult no-choice trials. Test plants were selected on relatedness to water hyacinth, similarity in habitat and on economic importance. Full nymphal development was recorded on Heteranthera callifolia, Pontederia cordata (pickerelweed) and Canna indica (canna) under quarantine laboratory conditions. Pickerelweed and canna are introduced species and are potentially invasive in South Africa, and are therefore of no conservation concern. Of the other native African Pontederiaceae, E. natans supported development of the grasshopper nymphs, but the lack of emergent leaf material suggests that the plant will not sustain a population, and Monochoria africana did not support full development of the nymphs. The adult females were not able to oviposit on the thin petioles of H. callifolia and only one eggpacket was recorded on M. africana, suggesting these two species are not at risk. Results from the region of origin show that Cornops aquaticum is an oligophagous insect on the Pontederiaceae family of plants, with a strong preference for water hyacinth. In South Africa, we intend to conduct further nymphal and adult choice trials which will better represent the field situation to further quantify the risk to native Pontederiaceae.