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United States Department of Agriculture

Agricultural Research Service


item White, S
item Tipping, Philip
item Becnel, James

Submitted to: Biological Control
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/24/2006
Publication Date: 6/15/2007
Citation: White, S.E., Tipping, P.W., Becnel, J.J. 2007. First isolation of a Helicosporidium sp. (Chlorophyta: Trebouxiophyceae) from the biological control agent Cyrtobagous salviniae (Coleoptera: Curculionidae). Biological Control. 40:243-245.

Interpretive Summary: Classical biological control of weeds involves the controlled reunification of natural enemies and the host plant which has usually become a serious weed in their new range. Insects are the most frequently used natural enemies and, once their host range has been determined and permits gained, they are released on the target weed. However, as part of the controlled release, the biological control organisms must be screened to avoid introducing unwanted organisms like diseases or nematodes which may reduce the effectiveness of the agent or, less likely, cause problems to non-target species. In the course of routine quarantine screening, we detected a new species of Helicosporidium in a shipment of Cyrtobagous salviniae from South Africa. The insect is perhaps the most successful aquatic weed biological control agent, repeatedly controlling giant salvinia on multiple continents. This type of organism is actually a type of parasitic algae which has unknown effects on C. salviniae. By intercepting this pathogen, we were able to release disease-free agents which went on to successfully control giant salvinia in Texas and Louisiana.

Technical Abstract: Cyrtobagous salviniae (Coleoptera: Curculionidae) is a weevil that has been introduced into at least 16 countries as a biological control agent for the floating fern, Salvinia molesta. Screening in Florida of C. salviniae imported from South Africa found a pathogen identified as a previously unknown species of Helicosporidium (Chlorophyta: Trebouxiophyceae). Fresh cysts measured 5.1 x 4.8 ìm and ultrastructural examination demonstrated the presence of three ovoid cells surrounded by a filamentous cell. Cysts of this pathogen were isolated and transmitted to the alternate hosts Helicoverpa zea and Anopheles quadrimaculatus. This is the first report of a pathogen from Cyrtobagous salviniae and demonstrates the need for and value of screening and monitoring biological control agents for pathogens prior to introduction. Releasing healthy C. salviniae not only enhances the chances for successful control of S. molesta but also reduces the risk for the inadvertent introduction of pathogens that may have undesirable and unexpected impacts on native fauna.

Last Modified: 06/22/2017
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