Submitted to: Society for Invertebrate Pathology Annual Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/18/2002
Publication Date: 8/18/2002
Citation: REBELO, M.T., BECNEL, J.J., CENTER, T.D. IMPACT OF A NEW SPECIES OF MICROSPORIDIA ON TWO WEEVILS, NEOCHETINA EICHHORNIAE AND N. BRUCHI, BIOLOGICAL CONTROL AGENTS OF WATER HYACINTH (EICHHORNIA CRASSIPES). PROCEEDINGS OF THE ANNUAL MTG OF THE SOCIETY FOR INVERTEBRATE PATHOLOGY. 2002.p.70.
Technical Abstract: Water hyacinth (Eichhornia crassipes) is an exotic aquatic weed that clogs natural waterways, displaces native vegetation and degrades wildlife habitat. Two closely related South American weevils, Neochetina eichhorniae Warner and N. bruchi Hustache were first introduced into Florida in 1972 and 1974, respectively, and from there worldwide to other countries to control this plant. The success of these introductions has been variable with the reasons for poor performance or failure to establish being unclear. We suspected that entomopathogenic organisms, particularly a new microsporidian species found in Florida, might be at fault. We therefore evaluated this microsporidia to determine it's impact on these biological control agents. Infections in N. eichhorniae were typically found to be systemic with the mid-gut, Malpighian tubules, and fat body heavily infected. Infections in N. bruchi are typically restricted to the mid-gut. Development of the microsporidium is completely haplokaryotic producing large sporogonial plasmodia and eventually sporophorous vesicles containing up to 50 uninucleate spores. Morphological and molecular studies are in progress to determine the taxonomic placement of this species. Field and laboratory studies to determine the natural infection levels of this new microsporidium and the impact of microsporidiosis on the survival and reproductive capacity of the Neochetina spp. were conducted with adults collected from 5 sites in South Florida over a 2-year period (2000-2001). N. eichhorniae adults had higher levels of microsporidia infection than N. bruchi both on a yearly basis (average of 9.3% vs. 4.4%; n=1300) and a seasonal basis (winter: 10.4% vs. 3.6%; spring: 9.2% vs. 4%; summer: 9.6% vs. 6.4%, and fall: 8% vs. 3.6%). The sublethal effects associated with this pathogen when compared to healthy adults (n=25 in each group) were expressed by 1) lower fertility rates where N. eichhorniae produced an average of 51.0±48.1 eggs when infected vs. 135.2±18.5 when healthy, while infected N. bruchi produced an average of 44.6±20.4 eggs vs. 159.0±14.9 when healthy and 2) a shorter life span in infected adults (72.9±40.4 days in N. eichhorniae and 63.9±34.7 days in N. bruchi ) when compared with healthy ones (102.3±27.0 days in N. eichhorniae and 94.8±19.2 days in N. bruchi). This new information on the presence and adverse impact of this pathogen (which decreased the survival of both weevil species by 30% and reduced their reproductive capacity by 72% in N. bruchi and 62% in N. eichhorniae) demonstrates the importance of selecting disease-free weevils for introductions into new regions to control this aquatic weed and suggests that this might be an important consideration in all biological control programs .