Progress 06/20/07 to 09/30/09
Outputs
OUTPUTS: The intracellular microsporidian parasite, Thelohania solenopsae, shows promise as a biological control pathogen against the red imported fire ant (RIFA), Solenopsis invicta. However, the horizontal transmission of the parasite is not well characterized, and understanding of the various routes of transmission is important to the further development of this ant pathogen as a biological control agent in a bait formulation. The experimental transfer of parasite spores was simulated in ant colony feeding trials by developing semi-solid nutrient substrates that incorporated appropriately sized fluorescent microspheres (1.8 to 7.2 um in size) as surrogates for the various sized spores. A selection of microsphere-ladened semi-solid lipid, protein and carbohydrate substrates were evaluated in feeding trials of monogyne and polygyne RIFA colonies with and without parasite infection. All ant castes and stages as well as the "midden piles" (ant trash piles) were evaluated for the presence of fluorescent microspheres in these ant colony feeding trials. The importance of the meconium from pupating larvae was evaluated by examining the meconia of larvae from experimentally fed colonies for the presence of fluorescent microspheres. The importance of midden pile in transfer of parasites was also evaluated by transferring microsphere-ladened midden piles to uninfected colonies and subsequently analyzed for the spread of the spheres through the colony. To further evaluate the various nutrient substrates as baits, the viability of Thelohania spores in nutrient substrates was tested over a 10 week period. PARTICIPANTS: PI: Karen Snowden, Associate Professor, Department of Veterinary Pathobiology, College of Veterinary Medicine, Texas A&M University CoInvestigator: S. Bradleigh Vinson, Professor, Department of Entomology, College of Agriculture and Life Sciences, Texas A&M University Training opportunity: PhD student and subsequent Postdoctoral Fellow: Sonia Kjos (PhD Entomology, Texas A&M University) TARGET AUDIENCES: Not relevant to this project. PROJECT MODIFICATIONS: Not relevant to this project.
Impacts
A number of recipes of semi-solid substrates were evaluated as a bait matrix. Three semi-solid substrates composed of carbohydrate, lipid or protein were tested in bait feeding simulations using four sizes of fluorescent microspheres (1, 2.2, 3.7 and 6 um spheres) to represent the various sizes of Thelohania spores. Uniform distribution of microspheres in the baits was determined by repeated sampling of the substrates. Field collected RIFA colonies were characterized as monogyne/polygyne and as Thelohania positive or negative and maintained in experimental conditions. Colonies were starved for 24 hours and then provided the microsphere substrate baits for 3 days. Subsequently, adults of all castes and 4th instar larvae were evaluated for the presence of microspheres. The lipid substrate bait was most success in disbursing microspheres to colonies (n = 6) even though the average consumption rate of the bait (35.5%) was the lowest of the 3 substrates. Both reproductive and non-reproductive 4th stage larvae contained the high number of microspheres of all sizes. Female alates and dealates/queens sporadically contained lower numbers of microspheres of all sizes. Workers contained no microspheres. In colonies (n = 6) fed the protein substrate bait, the average bait consumption rate was much higher (80%). Both reproductive and non-reproductive 4th stage larvae contained microspheres of all sizes at lower levels and on a less consistent basis. No adult ants contained microspheres. The average bait consumption for colonies (n = 8) fed the carbohydrate substrate baits was also high (80%), however microspheres of all sizes were only found sporadically at low levels in reproductive and non-reproductive larvae. The microsphere distribution and nutrient substrate consumption appear to be similar in monogyne and polygyne colonies, and the presence or absence of Thelohania parasites does not appear to influence microsphere distribution or nutrient substrate consumption. Fourth instar larvae near pupation were removed from colonies fed the microsphere substrate baits and allowed to pupate. Microspheres of all sizes were present in meconia in varying numbers, so we believe that this is a possible route of horizontal transmission of Thelohania through the ant colony. Regardless of the substrate, variable numbers of microspheres of all sizes were found in midden piles of substrate-fed colonies at multiple time points. Midden piles of colonies fed the lipid substrate bait showed the most consistent presence of spheres in high numbers. To evaluate the viability of Thelohania spores in a simulated bait, spores were incorporated into carbohydrate and protein substrates and evaluated for spore viability over a 10 week period. Spores showed a slight decrease in viability starting at 7 weeks. These results are encouraging, suggesting that the parasites should be stable in a bait formulation that could be developed on a commercial basis. Clearly, the semi-solid lipid substrate containing microspheres as a model indicates that a lipid substrate matrix is the optimum choice for continued development of a Thelohania-containing bait.
Publications
- Snowden K and SB Vinson. 2008. "Simulation of horizontal transmission of Thelohania solenopsae in the Red Imported Fire Ant (Solenopsis invicta) using fluorescent microspheres in nutrient substrates" Imported Fire Ant and Invasive Ant Conference, Mar 24-26, 2008. Charleston, South Carolina
|
Progress 01/01/08 to 12/31/08
Outputs
OUTPUTS: Collaborative research with Dr. Bradleigh Vinson (ENTO, COALS) continues, working with the development of the microsporidian parasite, Thelohania solenopsae as a potential biological control agent against the red imported fire ant, Solenopsis invicta. To determine how parasites are horizontally transmitted within a colony, a model system using 4 sizes of fluorescent microspheres in various nutrient substrates was developed. The microspheres simulated the various sized parasite spores that have been identified for this parasite. Feeding trials were conducted in monogyne (single reproductive queen) and polygyne (multiple reproductive queens)colony forms. The role of the male ant in parasite transmission was explored by tracking fluorescent microspheres in male alate ants. Additionally the male reproductive organs were examined by Calcofluor M2R fluorescent staining and microscopy to evaluate the presence of parasites in those organs. PARTICIPANTS: collaborative work continues between the PI (Snowden) and Dr. S. Bradleigh Vinson (ENTO, COALS). TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
A model system using 4 sizes of fluorescent microspheres in various nutrient substrates was used to simulate horizontal transmission of parasite spores within the ant colony. In feeding trials, all sizes of microspheres were found in larvae, workers and queens. The lipid-based nutrient substrate was the preferred substrate. No differences were noted between microsphere distribution in monogyne vs polygyne colonies. No differences were noted between microsphere distribution in parasite infected and uninfected colonies. These data continue to support the research hypothesis that this parasite has potential as a biological control agent administered through a commercial bait product containing parasite spores. However, these data do not clarify the biological reasons for the multiple types of spores. The different sized microspheres do not segregate into various developmental stages or ant castes, as was anticipated. Therefore, the various parasite spore types are not differentially important in horizontal parasite transmission, or the nutrient substrates with microspheres are not an effective model of parasite transmission of various sized spores. The reproductive tract of male alate ants were examined microscopically, and parasite spores were associated with that organ. This observation suggests that the male ant may contribute to parasite transmission via the reproductive tract during mating. This possible previously undocumented route of parasite transmission should be confirmed.
Publications
- No publications reported this period
|
Progress 01/01/07 to 12/31/07
Outputs
OUTPUTS: The collaborative research effort with Dr. Bradleigh Vinson (Professor) Department of Entomology, College of Agriculture and Life Sciences, TAMU, continues working on the development of the microsporidian parasite, Thelohania solenopsae, as a potential biological control agent against the red imported fire ant, Solenopsis invicta (RIFA). A model of horizontal transmission for the parasite has been developed. To simulate parasite spore transmission, appropriately sized fluorescent microspheres have been incorporated into lipid, protein or carbohydrate nutrient substrates and fed to parasite infected or uninfected monogyne or polygyne RIFA colonies. To date, the semi-solid lipid substrate is most efficient in distributing the microspheres in the ant colonies, suggesting that this substrate would be the best choice in bait development. Although experiments are in progress, parasite infection status or the mono/polygyne status of individually tested colonies does not appear to
influence nutrient uptake or bead distribution, suggesting that this approach towards bait development is broadly applicable.
PARTICIPANTS: Dr. S. Bradleigh Vinson (Professor) Department of Entomology, College of Agriculture and Life Sciences, Texas A&M University Dr. Asha Rao (Post-doctoral Research Associate) Deparment of Entomology, College of Agriculture and Life Sciences, Texas A&M University
Impacts
Research data generated during this period continue to support our long-term goal of developing Thelohania solenopsae as a biological control agent that has the potential as a commercial bait product that can augment or substitute for pesticide use in fire ant control.
Publications
- No publications reported this period
|
|