Influence of plant size and species on preference of Cyrtobagous salviniae adults from two populations

Adults from two populations (Brazil and Florida) of Cyrtobagous salviniae were bioassayed to determine if they exhibited a preference for either Salvinia minima or Salvinia 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 were 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.