|
Description:
|
The floating aquatic weeds common salvinia (Salvinia minima Baker ) and giant
salvinia (Salvinia molesta Mitchell ) degrade aquatic systems through fast , mat forming
growth . The Salvinia specialist weevil Cyrtobagous salviniae Calder and Sands has
been used to reduce the severity of giant salvinia infestations and associated with
reduced severity of common salvinia infestations . Genetically , morphologically and
biologically distinct strains of C . salviniae exist , but their relative potential for success as
biological control agents of Salvinia species has not been evaluated . This thesis (1 )
describes a recirculating water system designed for conducting such studies and (2 )
reports the results of C . salviniae strain comparisons .
A recirculating water system with a high degree of replication and minimal
variation in water flow , temperature and light intensity was used for laboratory
experiments using sixty -day temperature profiles averaging 31 .4 , 26 .5 and 8 .0ºC
derived from surface water temperatures measured at lakes in expected range of Salvinia
species in the North America . Larval and adult population numbers of two C . salviniae strains (Australia and Florida ) were determined for each temperature profile along with
feeding induced plant necrosis on both Salvinia species . Australia C . salviniae had
lower survivorship rates to adulthood on common salvinia than did Florida C . salviniae
at the 31 .4 and 26 .5ºC temperature profiles . Neither strain reproduced , and no
significant between -strain differences in plant necrosis were detected at the 8 .0ºC
temperature profile . At 31 .4ºC there were no significant differences in adult counts ,
larval counts or plant damage between the two strains on giant salvinia . At 26 .5ºC ,
however , significantly fewer larvae were collected from initially released adults and
significantly less plant necrosis was associated with weevil feeding by Florida strain
compared to Australia strain weevils . These results may have arisen from comparing
Australia weevils from a growing colony to Florida weevils from a declining colony .
Overall , the results indicate that only Florida C . salviniae should be released against
common salvinia . Florida C . salviniae may be equally suitable to Australia C . salviniae
for releases against giant salvinia , but further study is needed to fully assess the potential
for using Florida C . salviniae against giant salvinia . |