In the search for specific natural enemies to control two invasive aquatic plants (IAP) from South America, Ludwigia grandiflora subsp. hexapetala (Onagraceae) and Myriophyllum aquaticum (Haloragaceae), taxonomic challenges associated with two Lysathia Bechyné, 1959 (Chrysomelidae; Alticini) species had to be resolved. Lysathia flavipes (Boheman, 1859) exhibits significant morphological variation, causes heavy damage to both IAPs, and may represent more than one species due to the phylogenetic gap between hosts. Additionally, an undescribed Lysathia species (previously published as Lysathia sp.), sourced from Brazil, has been successfully used as a control agent for M. aquaticum in South Africa since 1994. An integrative taxonomic approach combining genetic and morphological analyses was employed. A lectotype and paralectotypes for Graptodera flavipes Boheman, 1859 are here designated. Phylogenetic studies revealed that L. flavipes had greater genetic and morphological variation than originally described, and no evidence suggested that L. flavipes represented a species complex associated with its host plants. As a result, the species description was expanded. On the other hand, genetic and morphological differences such as body size, colouration, and genital structures further supported the description of Lysathia cilliersae Cabrera, sp. nov. and its differentiation from other closely related species, including L. flavipes and L. ludoviciana (Fall, 1910). Specimens of L. cilliersaesp. nov. collected in Misiones, Argentina, matched those from South Africa. Genetic sequences correlated with morphological vouchers, images, and illustrations of morphology and genitalia, as well as new distribution records, are provided. This research contributes to the taxonomic knowledge of the Lysathia genus and supports accurate species identification in applied entomological contexts, such as biological control programmes.

Taosa longula Remes Lenicov (Hemiptera: Dictyopharidae), a planthopper native to South America, is a candidate for the biological control of water hyacinth, Eichhornia crassipes (Mart.) Solms-Laubach (Pontederiaceae), a serious weed worldwide. Biological control requires agents that are not only specific but also effective. Damage caused by sap-sucking insects is difficult to assess. In this work we designed an experimental and analytical procedure to evaluate the potential damage of T. longula on water hyacinth. The damage that T. longula causes to the clonal reproduction, biomass production, and growth of water hyacinth was studied through a paired greenhouse trial with floating cages. The performance of the plant, starting from two plants per treatment, was evaluated at different insect densities (5, 10, 15 and 20 nymphs per cage) until all the nymphs moulted to adults. The tests showed that individual growth and biomass production of water hyacinth was reduced due to the effect of the insect feeding above five nymphs per cage. The number of new plants produced by clonal reproduction was only significantly different above 15 nymphs per cage. These results suggest that this planthopper could be an effective agent for the biological control of water hyacinth.

In the search for insects as biological control agents for the water primrose, the delphacid Pissonotus paraguayensis (Delphacidae) was found on Ludwigia grandiflora subsp. hexapetala (Onagraceae) in a wetland of Central East Argentina. The morphology of the unknown females (brachypterous and macropterous) and immature stages are described and illustrated. Adults and nymphs were collected in wetlands of Del Plata River Basin, from Buenos Aires to the northeastern part of Argentina. A rearing methodology was developed to perform biological studies. Both winged forms and structural features of the female genitalia are described for the first time at the genus level. Eggs and immature stages are described and keyed; fifth nymphal instars may be easily recognised by the yellowish colouration, blackish on dorsal of head, thorax and abdomen with conspicuous yellowish pits, ventrally only darkened on base of frons extended to lower level of eyes and dorsal surface of antennomeres I and II, and legs with distinctive black marks at femoro-tibial joint and apex. The geographical distribution is updated, expanding its range into Argentina, making Buenos Aires the southernmost limit of the genus in America. Biological information of the species is also reported here: life cycle, fecundity, oviposition behaviour, and host plant. Field observations showed that P. paraguayensis breeds, feeds, and causes damage to L. g. subsp. hexapetala. This delphacid presents a certain degree of specificity to the Ludwigia species in the Jussiaea section in host specificity tests. More studies are required to test this species as a potential biological control agent.

The aim of this paper is to shed light on the boundaries of two sympatric species of Cuernavaca, C. inexacta and C. longula, to enable further ecological studies. Species in this genus are associated with water hyacinths in wetlands of Northeastern Argentina (Paraná-Paraguay waterway system) and the Peruvian Amazon. This work lists new host records for Cuernavaca, which include Pontederia crassipes, P. cordata, P. subovata and P. rotundifolia (Pontederiaceae). A redescription for C. inexacta with new diagnostic genitalic features is also provided, as well as an updated identification key and a distribution map. The genus is distributed throughout Central and South America, reaching north and central Argentina in its southernmost distribution.