Weevils Listronotus marginicollis and L. cinnamomeus that feed on Limnobium and Myriophyllum in Argentina.

The weevil Listronotus (=Hyperodes) cinnamomeus (Hustache) appeared to be host specific on frogbit, Limnobium stoloniferum (G.F.W. Meyer) Griseb. In the field, we collected it only from L. stoloniferum. In the laboratory, adults fed only on L. stoloniferum and slightly on 4 other test plants, among 22 plant species tested. The adults fed on the leaves and the larvae mined the leaves and pupated in the petiole. Populations reached I adult per 3 or 4 plants during the summer. The weevil Listronotus marginicollis (Hustache) appeared to be host specific on parrotfeather, Myriophyllum aquaticum (Velloso) Verde (=M. brasiliense). In the field, we collected it only from M. aquaticum. In the laboratory, adults fed heavily on M. aquaticum, moderately on L. stoloniferum, and slightly on 12 other test plants among 43 plant species tested. The adults fed on the leaves of M. aquaticum and often killed the terminal bud. The larvae tunnelled in the stem, both above and below the waterline; 79% of the stems were damaged in one area. Some species of aquatic macrophytes of the genera Limnobium (frogbit) and Myriophyllum (watermilfoil, parrotfeather) are aquatic weeds of economic importance in the southeastern United States (Weldon et al. 1969). These genera have closely-related species native in southern South America. One of them, M. aquaticum (Velloso) Verde (=M. brasiliense Camb.), was introduced into the United States from South America. Cabrera (1965, 1968) recorded 1 species of Hydromystria (now =Limnobium stoloniferum (G.F.W. Meyer) Griseb.) and 2 species of Myriophyllum (M. aquaticum and M. elatinoides Gaudichaud) from Buenos Aires Province, Argentina. We report here our observations and tests on the biologies and host ranges of two weevils that we found attacking these plants in Argentina. These are the weevils Listronotus marginicollis (Hustache) on Myriophyllum and L. cinnamomeus (Hustache) on Limnobium. Neither of these weevils are known to occur outside of South America. We made observations and tests to determine if these weevils might be candidates for biological control of Myriophyllum and Limnobium in the United States. The tests were made from 1972 to 1975 during the course of our main project on biological control of waterhyacinth Eichhornia crassipes (Mart.) Solms (DeLoach and Cordo 1976; DeLoach et al. ' Coleoptera: Curculionidae. 2 Accepted for publication February 12, 1982. 3 Present address of thejunior author: Grassland, Soil and Water Research Laboratory, ARS, USDA, P.O. Box 748, Temple, TX 76503. 4 C. W. O'Brien, Florida A&M University, Tallahassee, FL 32307.