Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2003
Publication Date: 6/20/2004
Citation: White, W.H., Reagan, T.E., Smith, J.W., Salazar, J.A. 2004. Refuge Releases of Cotesia flavipes (Hymenoptera: Braconidae) Into the Louisiana Sugarcane Ecosystem. Environmental Entomology. 33(3):627-632. Interpretive Summary: With respect to total economic value, sugarcane is the most important row-crop grown in Louisiana and the sugarcane borer is the most important insect pest of sugarcane in Louisiana. To control the borer, growers presently must rely heavily on insecticides, a practice both expensive and environmentally disruptive. One alternative to applying insecticides is to introduce a very small wasp from the tropics into Louisiana sugarcane fields where it will sting and kill sugarcane borers. USDA researchers have demonstrated that the wasp can find and kill sugarcane borers during the summer when the borers are feeding on the stalks of sugarcane; however, the wasp fails to survive from year to year. The method is not practical if the wasp has to be reintroduced every year. The tropical wasp was carefully monitored to determine if it is able to survive the freezing winters of Louisiana. The researchers found that the wasp can survive the winter; however, in the spring when it needs to feed on the sugarcane borer to survive, the wasp appears to be unable to find the sugarcane borers because they are in sugarcane plant tissues below ground level. The cotesia wasp is effectively used in the tropics to control sugarcane borers; however, it does not appear to be able to adapt to the environmental conditions of Louisiana. Entomologists are seeking other insects that can survive in Louisiana and help control the sugarcane borer without the use of insecticides.
Technical Abstract: After repeated failures to establish Cotesia flavipes (Cameron) as a parasitoid of the sugarcane borer, Diatraea saccharalis (F.), in Louisiana sugarcane fields (interspecific hybrids of Saccharum spp.), four release refuges were identified as sites for an intensive study of the crop, host, and parasitoid interaction for a full crop cycle. These refuges were maintained from June 2001 - June 2002 with minimal disturbance to encourage the establishment of C. flavipes and to identify if this management approach might be used to introduce C. flavipes throughout the Louisiana sugarcane agroecosystem. Refuges were managed in a manner such that: 1) sugarcane borer larvae were abundant as hosts for the parasitoid, 2) predation of parasitoids by red imported fire-ant, Solenopsis invicta (Buren), was minimized, 3) host and parasitoid were not exposed to insecticide applications that might occur in sugarcane fields to control economically damaging sugarcane borer infestations, 4) a perceived critical mass of parasitoids was maintained through repeated releases, and 5) the sugarcane was not harvested to enhance overwintering opportunities for C. flavipes. Cotesia flavipes was successfully recovered in all established refuges, with parasitism of sugarcane borer larvae averaging 11% from ablated stalks infested with hosts and placed in refuges, and 20% from naturally infested stalks during the period from June 2001 to June 2002. Parasitoids were successful in preventing economic damage (< or = 10% bored internodes) at only one of the four refuges - with two refuges heavily damaged (29% bored internodes). We demonstrated for the first time that C. flavipes could overwinter in Louisiana; however, parasitoids were not collected during May of the following spring. The ability of the parasitoid to utilize first-generation sugarcane borer larvae is the limiting factor preventing establishment of C. flavipes in Louisiana sugarcane. In May, the sugarcane stalks have not formed internodes, which may preclude important host finding, and host acceptance cues such as tunnel entrance, silk in the entrance. Unlike sugarcane produced in other areas, sugarcane in Louisiana is a uniformly young crop following harvest and therefore no suitable sites are available to perpetuate parasitoid populations during the critical time before internode formation.