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Pistia stratiotes L. (Araceae) is an important weed in many waterways worldwide. The South American weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae) and the planthopper Lepidelphax pistiae Remes Lenicov (Hemiptera: Delphacidae) are specific herbivores of P. stratiotes. Both species, plus the oligophagous moth Samea multiplicalis Guenee (Lepidoptera: Crambidae), were released in a P. stratiotes-infested lake in the suburbs of Buenos Aires, Argentina, where previous sampling indicated that specific herbivores were absent. The weevil and the planthopper established and covered the whole lake in under two months. The moth may have also established but its numbers were very low and erratic. Plant cover, biomass per square metre, and individual plant size decreased markedly within a year after the release of the insects. Concomitantly, other floating macrophytes appeared in the lake. Insect abundance was related to mean monthly temperature and light hours, but not the other insect speci...

Pistia stratiotes L. (Araceae) is an important weed in many waterways around the world. The South American weevil Neohydronomus affinis Hustache (Coleoptera: Curculionidae) is a successful biocontrol agent for this weed but additional agents are needed for some areas. The planthopper Lepidelphax pistiae Remes Lenicov (Hemiptera: Delphacidae) is a specific herbivore of P. stratiotes and is highly damaging in laboratory conditions. A field experiment was designed to evaluate the damage potential of L. pistiae compared to N. affinis and to assess the potential for competition between the two herbivores. Both herbivore species were reared inside floating cages on a P. stratiotes-infested lake. Plant growth indices assessed were clonation levels, biomass and plant diameter. The growth indices of plants exposed to the herbivores, individually and combined, were comparable, and significantly lower than in the control treatments. Population levels of N. affinis inside the cages were not significantly different when alone or together with L. pistae. Conversely, the density of L. pistiae was significantly lower in combination with the weevil. This suggests that L. pistiae is a damaging herbivore that will not reduce the biological control effectiveness of N. affinis.

The delphacid Lepidelphax pistiae was found on water lettuce in Argentina. Nymphs and adults did not survive past seven days on 29 species of test plants, and no progeny were produced. In contrast, survival and reproduction were high on water lettuce. Results suggest that L. pistiae is monospecific to water lettuce. Fil: Cabrera Walsh, Guillermo José. Fundación para el Estudio de Especies Invasivas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Maestro, Mariano. Fundación para el Estudio de Especies Invasivas; Argentina Fil: Sosa, Alejandro Joaquín. Fundación para el Estudio de Especies Invasivas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Tipping, Philip W.. United States Department of Agriculture; Argentina. United States Department of Agriculture. Agricultural Research Service. Invasive Plant Research Laboratory; Estados Unidos