Submitted to: Biological Control
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/12/2004
Publication Date: 12/8/2004
Citation: Tipping, P.W., Center, T.D. 2004. INFLUENCE OF PLANT SIZE AND SPECIES ON THE PREFERENCES OF CYRTOBAGOUS SALVINIAE ADULTS FROM TWO POPULATIONS. Biological Control. 32:263-268.2005. Interpretive Summary: Giant and common salvinia are serious aquatic weeds which threaten fresh water wetlands throughout the southeastern and western US. Giant salvinia is considered to be a greater problem than common salvinia. Herbicides and mechanical controls are largely ineffective and expensive. Biological control is one tactic which may provide sustainable control at a landscape level. A small weevil, Cyrtobagous salviniae, is available for use but there have been several questions about which population of weevil (Brazil or Florida) is best for a particular salvinia species. Weevils from both populations are identical except for size where adults from Brazil are larger than adults from Florida. The Brazil weevils selected plants on the basis of size, not species. Florida adults also selected plants this way, although they were less sensitive to plant size than the Brazil weevils. Either population of weevil would be appropriate for use in a biological control project targeting giant salvinia.
Technical Abstract: Adults from two populations (Brazil and Florida) of Cyrtobagous salviniae were bioassayed to determine if they exhibited a preference for either Salvinia minima or S. molesta. Adults did not discriminate between host species in initial tests that evaluated the tertiary growth form. Further tests which compared two growth forms (primary and tertiary) as well as plant species, found that adults from the Brazil population consistently preferred larger (tertiary) plants without regard for host species. Weevils from the Florida population showed a similar, but less distinct, pattern of preference. Although adults from the Florida population survived equally well and experienced a similar pre-oviposition period on both plant species, they laid more eggs in S. molesta. Adults from the two populations differ in size: Brazil weevils are larger, which may explain their sensitivity to plant size as compared with the smaller Florida adults. Narrower rhizomes in S. minima may restrict usage of this species by the larger weevils, whereas smaller larvae may be better able to burrow in a wider range of plant sizes. Both weevil populations should be suitable biological control agents for use in programs targeting S. molesta.