Megamelus scutellaris (Hemiptera: Delphacidae), a biocontrol agent of water hyacinth, is not sufficiently specific for release in Australia

Abstract

Water hyacinth Eichhornia crassipes (Pontederiaceae) is one of the world's worst invasive species, responsible for damaging aquatic systems in many warmer parts of the globe including north America, Africa, Asia and Australia. The planthopper Megamelus scutellaris Berg (Delphacidae) has been released in USA and approved for release in South Africa for biocontrol of water hyacinth. We assessed this agent for suitability for release in Australia and found that a related native aquatic plant, Monochoria cyanea (Pontederiaceae) is within the fundamental host range of this insect. Adult survival, oviposition and development of nymphs to adult was equally high on M. cyanea as on the target species, although the quality of these next generation adults was lower than those reared on the target species. This demonstrates that M. scutellaris is not sufficiently specific for release in Australia. Nymphal development to adults occurred only in very low numbers on the three other Australian species of Monochoria. M. cyanea only occurs in Australia so M. scutellaris is still a possible water hyacinth biocontrol candidate for other regions depending on the results of assessment of the risk to local species of Monochoria. This study demonstrates the effectiveness of modern biocontrol agent assessment and reinforces the importance of testing of local non-target species.