1a.Objectives (from AD-416)
To seek and identify natural enemies of Cabomba carloniniana (Fanworth) for potential use as biological control agents.

1b.Approach (from AD-416)
In conjunction with CSIRO, the program will involve delineating the range of Cabomba in South America, particularly northern Argentina and adjancent countries; collecting and curating flora and fauna specimens; maintaining specimen data base; preparing and shipping specimens for identification to CSIRO; studying the biology of selected species; and conducting host range studies in the field and the laboratory.

3.Progress Report
Rearing techniques under lab conditions were improved. Plants are grown in three 1,000-litre glass pools equipped with four sugar/yeast CO2 generators. However, as the size and profusion of plants in the tanks do not allow observations on the weevil Hidrotimetes natans, individual observations and rearing of the weevil are carried out in 3-liter jars, and 8-liter clear polycarbonate cylinders.

Flower buds and primordia, and young roots were collected and preserved to determine hybridization and evaluate fertility of each population, and karyotype. The objective of this study is to determine if there are population structure traits or hybridization events that may help explain cabomba’s weedy behavior.

Three new Cabomba sites have been found in Argentina, outside the usual range, two in the province of Formosa, and one in northern Buenos Aires. None of the samples collected in these sites, however, had insect natural enemies, so the Iberá wetlands, in Corrientes, remains as the most rich and reliable collecting area. So far H. natans larvae have been found only in C. caroliniana; so are the vast majority of adults, although a few (< 3%) can also be found on E. najas and Utricularia platensis, the other submerged plants coexisting with cabomba, growing mixed with it in the field.

Adults of H. natans have been released in tanks with Egeria densa and Potamogeton spp. for non choice tests. No larvae or pupae were ever observed, nor was adult feeding. This and field evidence of other aquatic plants co-occurring with C. caroliniana, confirm the specificity of this weevil.

Field ecology studies were conducted and a succession between C. caroliniana and E. naias was observed in the submerged plant community in the Cabomba environments. This succession is not season dependant, as thought before, and does not follow the same pattern in nearby sites. The underlying causes of these dynamics are still unknown.

Methods used for the monitoring of this subordinate project included periodic phone calls and e-mail exchanges with Mic Julien (Commonwealth Scientific and Industrial Research Organization (CSIRO) Entomology European Laboratory, Montpellier, France) and Shon Schooler (CSIRO Entomology, Indooroopilly, Australia). Also, three quarterly reports were prepared and delivered to the funding agency.