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 in South Africa. Both the adults and the nymphs are very damaging to water hyacinth plants. The laboratory host range was determined through nymphal and adult no-choice trials. The 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, Eichhornia 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 Heteranthera callifolia and only one eggpacket was recorded on Monochoria africana, suggesting these two species are not at risk. Results from the region of origin show that C. 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. WATER hyacinth is considered to be the most important aquatic weed in the world (Center 1994; Wright and Purcell 1995). In South Africa, it was first recorded in the early 1900s. Since then the weed has become invasive throughout southern Africa, mainly as a result of human activities (Jacot Guillarmod 1979). Attempts to control the weed have led to different control options being developed, including herbicidal control, mechanical control and biological control. In South Africa, the biological control program has been in place since 1974, with an interruption of 8 years between 1977 and 1985 (Hill and Cilliers 1999). In the course of the program, five arthropod natural enemies were released against the weed: Neochetina eichhorniae, Neochetina bruchi, Orthogalumna terebrantis, Eccritotarsus catarinensis and Niphograpta albiguttalis. Even with these species released there is a perception that, in South Africa, the correct ‘suite’ of insects to biologically control the weed has not been introduced. As a result, additional natural enemies are being sought for control of water hyacinth. In this paper we discuss the suitability of Cornops aquaticum, a grasshopper species, for release in southern Africa. Information from the Literature Cornops aquaticum was identified by Perkins (1974) as being one of the most damaging insects associated with water hyacinth in the plant’s region of origin. However, it appears that fears regarding this insect’s host specifi* Weeds Research Division, Plant Protection Research Institute, Agricultural Research Council, Private Bag X134, Pretoria, 0001, South Africa. Email: Rietho@plant2.agric. za