Preliminary evaluation of Megamelus scutellaris Berg (Hemiptera: Delphacidae), a candidate for biological control of waterhyacinth

The planthopper Megamelus scutellaris (Hemiptera: Delphacidae) is a potentially valuable insect for biological control of waterhyacinth (Eichhornia crassipes (Mart.) Solms.: Pontederiaceae), a serious aquatic weed in many tropical and subtropical countries. Field surveys done in South America revealed that this insect is sympatric with waterhyacinth throughout the native range of the plant, from Peru to as far south as Buenos Aires Province, Argentina. The host range of this insect was preliminarily evaluated, as was its ability to damage the plant, in order to determine whether further study was warranted. Feeding was compared, using a preference index, among leaf disks of test plants in two multiple-choice experiments: one with and one without members of the family Pontederiaceae. A similar no-choice experiment employed various species of Pontederiaceae along with rice and maize. A paired oviposition choice experiment was done by caging gravid females on E. crassipes and Pontederia cordata plants and then counting eggs deposited as well as oviposition scars. The ability of the insect to damage waterhyacinth was assessed in a greenhouse by inoculating a single waterhyacinth plant with none, 10, or 20 adult planthoppers. The planthopper effect was measured by comparing plant biomass (dry weight) among treatments after 1 month. All of these studies suggested that M. scutellaris is host specific and has the ability to damage waterhyacinth. Some feeding and development occurred on other species in the family Pontederiaceae which may have been laboratory artifacts, but which mandates a cautious, further evaluation of this planthopper prior to its use as a classical biological control agent.