Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 5, 2003
Publication Date: March 1, 2003
Citation: Tipping, P.W., Center, T.D. 2003. CYRTOBAGOUS SALVINIAE (COLEOPTERA: CURCULIONIDAE) SUCCESSFULLY OVERWINTERS IN TEXAS AND LOUISIANA. Florida Entomologist. 86(1):92-93.2003. Interpretive Summary: Salvinia molesta D. S. Mitchell, an invasive floating fern, has invaded 12 states in the U.S. and is now well established in Texas and Louisiana. This plant quickly colonizes the surface of slow moving, fresh water bodies causing severe ecological and economical problems. Successful biological control programs targeting this weed have been conducted in at least 13 countries worldwide using a small weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae). After additional host range testing confirmed it's specificity to S. molesta, a general release permit was obtained for this species in a designated area in eastern Texas and western Louisiana. The first releases were conducted during October 10-11, 2001 when a total of 880 C. salviniae adults was released at four sites. Subsequent visits to these sites plus four control sites were conducted in December 2001 and March 2002. Further sampling was halted during the winter and resumed on March 25-27, 2002. Two of the four release sites yielded adult C. salviniae during hand searches with three and four adults found at those sites. It is unknown if these weevils were the original adults or progeny from the October, 2001 release. It is noteworthy, therefore, that adults of C. salviniae were able to persist or propagate over a period of 166 days despite temperatures that reached as low as -9.1 C and -7.1 C at Toledo Bend reservoir and Lake Texana, respectively. The former site is the most northern and the latter the most southern site.
Technical Abstract: A biological control project targeting giant salviniae, Salvinia molesta, passed an important milestone, namely, the survival of the introduced biological control agent, Cyrtobagous salviniae, over the winter of 2001-2002 at two sites in Texas and Louisiana. Initially, the insects were released in October 2001 and surveys in March 2002 yielded adults in two of the original four sites: Toledo Bend reservoir in Louisiana and Lake Texana in Texas. This insect is originally from southeastern Brazil. The area around Toledo Bend reservoir experienced 26 days during October 2001 through March 2002 when the minimum air temperatures were below 0 C. In contrast, only 7 days had minimal air temperatures below 0 C in the Lake Texana area. These temperatures were probably not maintained for long; in every case the daily maximum temperature was above 0 C. Other research demonstrated that S. molesta was killed when its buds were exposed to temperatures less than -3 C for 2-3 h. In many locations at these two sites, the plants were in coves and backwater areas sheltered from direct winds and protected by overhanging vegetation from the shoreline or adjacent floating plants like water hyacinth, Eichhornia crassipes (Mart.) Solms. These conditions likely buffered any negative temperature effects on the plants and insects. As expected, water temperatures lagged behind the colder air temperatures. This finding indicates that the Brazilian `type' of C. salviniae may survive the winter climate where S. molesta is extant in Texas and Louisiana. It may also indicate that the weevil is in the process of establishing sustainable populations in these areas.