Submitted to: Biocontrol
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/16/2005
Publication Date: 10/16/2006
Citation: Madeira, P.T., Tipping, P.W., Gandolfo, D., Center, T.D., Van, T.K., O'Brien, C. 2006. Molecular and morphological examination of cyrtobagous sp. collected from argentina, paraguay, brazil, australia, and florida. Biocontrol. 51:679-701 Interpretive Summary: Giant salvinia, Salvinia molesta, is established in the United States and has become a nuisance in Texas and Louisiana, forming thick mats which interfere with navigation and sport activities. Nuisance populations of giant salvinia have been controlled in many foreign countries, including Australia, by the use of the weevil, Cyrtobagous salviniae. This weevil has long been established on common salvinia, Salvinia minima, in Florida. This lab began the collection and release of the Florida weevil onto giant salvinia. However, following a preliminary molecular analysis of the Florida and Australian weevil, it appeared that the Florida weevil might be a different species from the Australian weevil (which originated in Brazil). Therefore, because of its past success, the Australian weevil was imported and released for biological control instead. However, the molecular analysis lacked a yardstick to compare the sequence differences between the two types. A sampling trip was organized to collect the Cyrtobagous salviniae weevil from its home range in Brazil, Argentina, and Paraguay. Samples of the very closely related (cryptic) species Cyrtobagous singularis were also collected to act as the yardstick. Results indicated that sequence differences between the two species were about 5X as great as the differences between the Florida and the Australian/Brazilian Cyrtobagous salviniae or between the Argentinian/Paraguayan and the Australian/Brazilian Cyrtobagous salviniae. This indicates that the Florida and Australian/Brazilian weevils probably are still the same species. A molecular tool is also presented which could be used to distinguish field populations of the 2 Cyrtobagous salviniae types.
Technical Abstract: Two members of the floating fern genus Salvinia (Salviniaceae), S. minima Baker and S. molesta Mitchell, have established in the United States. Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), long established on Florida S. minima, was released in Texas and Louisiana as a biocontrol agent for both species. Subsequently, mitochondrial sequence analysis (D2 expansion domain - 28S rRNA) suggested the Florida and Brazilian (used worldwide for biocontrol) C. salviniae might constitute cryptic species. In response, the Brazilian weevil was imported from Australia and released instead onto S. molesta. We sampled C. singularis Hustache and C. salviniae from their native ranges in Brazil, Argentina, and Paraguay and sequenced them (mitochondrial 28S rRNA D2 expansion domain) along with Australian and Florida samples. The genetic distance between C. singularis and C. salviniae samples is much greater (almost 5X) than the distance between either the Florida and Brazilian samples or the Brazilian and Argentinian/ Paraguayan C. salviniae samples. Since C. singularis and C. salviniae are cryptic species, the Florida and Brazilian populations (or for that matter Brazilian and Argentinian/Paraguayan) could reasonably be described as demes or ecotypes. Occurrence data indicates that, in parts of their ranges, C. salviniae and C. singularis are not only sympatric but also feed on the same species at the same site. While species preferences probably occur within local demes, both species seem capable of adapting to whichever Salvinia species is available. Finally, a polymerase chain reaction (PCR) primer was developed capable of distinguishing the Florida and Brazilian/Australian types.