Alpha diversity, population dynamics and interactions of ant assemblages were studied in a pecan orchard located in Mumford, Texas. The assemblages included the invasive species Solenopsis invicta Buren, known as the red imported fire ant (RIFA). The study addressed the major question of what is the response of the ant assemblage to the reduction of RIFA following insecticide applications (bait and contact insecticide) and the impact of these on individual species. To address this question three treatments were established in a 16 hectare area in the orchard. The treatments were randomly assigned in 1.33 hectare blocks with four replications and periodically monitored. Treatments were: 1) insect growth regulator (IGR) bait treatment (ExtinguishTM, active compound is 0.5% s-methoprene) applied twice in 2000 and once in 2001; 2) the contact insecticide chlorpyrifos (LorsbanTM) applied on tree trunks four times in 2000 and once in 2001; and 3) untreated Control. Blocks were sampled using pitfall traps, baited vials, direct sampling, and colony counts. Data were analyzed by using ANOVA-GLM with the LSD multiple comparison test to compare the effect of treatment on the ant assemblage (using the Shannon index) and the effect on individual species. Additionally, data obtained from Control plots were used to compare sampling techniques and to determine what method is most efficient for collecting ants in this agroecosystem. Shannon indices were estimated for each method and compared. The ant assemblage consisted of 16 ant species. S. invicta was the most abundant followed by Paratrechina sp. and Monomorium minimum. The IGR treatment consistently reduced RIFA (77%). Native ants were found to coexist with RIFA in the Control and chlorpyrifos plots at lower densities and maintained higher densities in IGR plots. Chlorpyrifos trunk treatment did not have a significant impact on RIFA or native ant densities. The native ant, Dorymyrmex flavus, was greater in IGR plots following RIFA reduction and higher densities were found to persist for more than two years after the last IGR treatment. During this period, D. flavus was observed carrying large numbers of dead RIFA, some taken inside the nest, and some disarticulated RIFA taken out of the nest. RIFA remains were accumulated in D. flavus middens, further indication of an important interaction between these two species. These results indicate D. flavus resisted reinvasion by RIFA.

Receptors that transport vitellogenin into oocytes are of vital importance to egg-laying species because they promote oocyte development. In this study, we describe the cloning of the first hymenopteran vitellogenin receptor (VgR) cDNA. Using reverse transcription polymerase chain reaction (RT-PCR) and both 5’- and 3’- rapid amplification of cDNA ends (RACE), cDNA fragments encompassing the entire coding region of a putative VgR from fire ant (= SiVgR) were cloned and sequenced. The complete SiVgR cDNA has a length of 5764 bp encoding a 1782-residue protein with a predicted molecular mass of 201.3 kDa. The deduced amino acid sequence of the SiVgR revealed that it encoded a protein belonging to the low-density lipoprotein receptor superfamily. The number and arrangement of modular domains of SiVgR are the same as those of mosquito and fruit fly VgRs, except there are only four Class A cysteine-rich repeats in the first ligand binding domain of SiVgR compared to five in the mosquito and fruit fly. The deduced amino acid sequence of the SiVgR exhibited 35% and 31% identity to those of the mosquito and fruit fly VgRs, respectively. Northern blot analysis demonstrated that the 7.4-kb SiVgR mRNA was present only in Northern blot analysis demonstrated that the 7.4-kb SiVgR mRNA was present only in ovaries of reproductive females − both alates (virgins) and queens (mated) and was more abundant in alates. The developmental profile of transcriptional expression was determined by semiquantitative RT-PCR. It showed that the SiVgR transcript increased 6-fold from 0- to 10-days after mating, then remained constant through 30 days. It also showed that the SiVgR transcripts increased with age in alate virgin females. The transcriptional expression of the SiVgR was up-regulated more than two-fold by methoprene, a juvenile hormone analog, as determined by using an in vitro system. This suggested the SiVgR gene is JH regulated.

Thelohania solenopsae Knell, Alan, and Hazard is an internal microsporidian that parasitizes the red imported fire ant, Solenopsis invicta Buren. This experiment studied the invasive interactions between the native United States ant, Monomorium minimum (Buckley), and S. invicta colonies infected with T. solenopsae and S. invicta colonies free of parasites. This study utilized S. invicta colonies of 100, 300, 600, 800, and 1000 workers to determine the ability of 1000 M. minimum workers to invade each S. invicta colony size. There was a significant difference in the time for M. minimum to invade S. invicta when comparing S. invicta colonies of 1000 workers infected with T. solenopsae to S. invicta colonies that were uninfected. It was also determined that there was a significant difference in the time for M. minimum to invade smaller uninfected S. invicta colonies as opposed to larger uninfected S. invicta colonies. There was no significant difference in the ability of M. minimum to invade smaller S. invicta colonies infected with T. solenopsae as opposed to larger infected S. invicta colonies. It was therefore concluded that S. invicta colonies infected with T. solenopsae were not able to defend their colony or prevent competing ants from invading as well as uninfected S. invicta colonies. This study also demonstrated that M. minimum is a significantly more invasive species when compared to S. invicta, invading S. invicta territories in every situation and doing so in a significantly shorter period of time than S. invicta colonies invaded M. minimum colonies.

Inclusion/exclusion field experiments demonstrated that the red imported fire ant, Solenopsis invicta Buren, did not affect the abundance of 49 groups of insects and spiders collected in pitfall traps. However, arthropod diversity was significantly greater (H' = 2.829) in exclusion plots relative to inclusion plots (H' = 2.763). Moreover, this study demonstrated that S. invicta can have an important impact upon cotton arthropod communities, including key predator species. Densities of ground beetles (Carabidae), spiders, lacewings (Chrysoperla spp.), and minute pirate bugs (Orius spp.) were significantly lower in the presence of S. invicta. However, populations of aphidophagous insects such as Hippodamia spp. and Scymnus spp. increased with cotton aphid (Aphis gossypii Glover) density early in the season. Abundance of cotton aphids was ca. 5x greater in inclusion plots, likely due to protection and tending by S. invicta. This increase was observed early in the season, though aphid populations did not reach economic levels. Predation of sentinel bollworm [Helicoverpa zea (Boddie)] and beet armyworm (Spodoptera exigua Hubner) eggs increased 20-30%, when S. invicta was present. Most predation of sentinel beet armyworm egg masses, measured via direct nocturnal observations, was due to S. invicta (68%) and cotton fleahopper [Pseudatomoscelis seriatus (Reuter)] (21%) in plots with S. invicta, and by the mite Abrolophus sp. (52%), spiders (13%) and minute pirate bug (13%) in plots without S. invicta. The frequencies of minute pirate bug, cotton fleahopper, S. invicta and native ants in beat bucket samples did not accurately reflect the frequency with which they were observed feeding on sentinel noctuid eggs. Overall, the results of these studies demonstrated that S. invicta was associated with declines in the abundances of minute pirate bug, spiders, and lacewing and with an increment in cotton aphid populations, though they did not reach the economic threshold. Moreover, S. invicta significantly increased predation of bollworm and beet armyworm eggs. All together, the results suggested that S. invicta has a net positive impact on cotton pest management.

Thesis(M.S.)--Auburn University, 2005. / Abstract. Includes bibliographic references.

Understanding of mechanisms that limit the abundance and distribution of species is central to ecology. The failure of mechanisms to regulate populations can result in population outbreaks. There have been two outbreaks of house mice in the past decade in central Florida. In my study, I examine the efficacy of landscape management in the form of mowing and plowed soil barriers to limit or prevent outbreaks of house mice in a former agricultural area. House mouse populations were highly variable, but were unaffected by mowing or plowed soil barriers. Red imported fire ants were ubiquitous in the study area regardless of land management treatments. Control of fire ants did not result in more house mice on treated plots.

The red imported fire ant, Solenopsis invicta, is an abundant and aggressive component of early-successional communities in the southeastern United States. After disturbance, it rapidly invades new habitats, and once there, it has strong competitive and predatory effects on the existing arthropod community. In upland coastal plain pine forests at the Savannah River Site in South Carolina, I conducted two studies of fire ant ecology. In my first study (chapter 1), I investigated the way in which fire ants colonize early-successional road and powerline cuts through forests, and I tested whether some of these linear habitats provided better fire ant habitat than others. I found that fire ant mound density (#/ha) was similar in narrow dirt roads and in wider roads with the same intermediate level of mowing disturbance, and that density was lower in wide powerline cuts where the vegetation is only removed every five years. Furthermore, mound density was greatest near the edges of cleared roads and powerline cuts and was also greater on the northern sides of roads and powerline cuts where there was less shading from the adjacent forest. Results from this study suggest that allowing increased shading from adjacent forest vegetation, especially along northern roadside edges, would limit the suitability of road and powerline cuts as fire ant habitat, thereby slowing invasion. In my second study (chapter 2), I examined the impact of fire ants on arthropod and plant species in early-successional forest gaps. In a tritrophic system, I tested whether the top-down effect of insect herbivore consumption by fire ants was strong enough to cascade through two trophic levels and improve plant growth and fitness. I compared this potential effect to that of other arthropod predators in the community. I found that fire ants controlled the level of tissue damage to plant leaves by herbivores, but that the damage was not severe enough to influence plant growth or fitness. Fire ants had stronger negative interactions with insect herbivores than other predators in the community, and for this reason, fire ants can be considered keystone predators. This project provides further evidence that fire ants successfully invade even small patches of early-successional habitat that exist within larger matrices of uninhabitable, late-successional forest, and that once there, they have a dramatic effect on the arthropod community. Restricting the amount of early-successional habitat within southeastern forests, either as permanent road and powerline cuts or as temporary gaps, would limit the potential for strong and detrimental effects by the invasive fire ant. / Master of Science

Higher densities of S. invicta in the United States relative to South America are explained mainly by the absence of natural enemies and low interspecific competition (IC). Despite advances in S. invicta management, broadcast insecticide baits remain as the primary tool for effective control. I studied interspecific interactions of ants and the use of baits on the management of S. invicta to test the following hypotheses: 1) relative abundance of native ants increases ~25% for bait treated sites compared to untreated, 2) behavioral dominance by S. invicta decreases ~10% in bait treated sites compared to untreated, and, 3) foraging by S. invicta on insecticide baits is higher ~10% in low native ant densities areas compared to high densities. Experiments were conducted on three sites with different densities of native ants (low, medium, high), but with similar densities of S. invicta. An enhanced BACI (Before/After-Control/Impact) design was used. Experimental units consisted of 0.4 ha plots. Three treatments were randomly assigned to units and replicated four times; 1) Slow acting bait, 2) Fast acting bait, 3) Untreated Control. Samples and observations were collected for several weeks before/after the treatments to account for temporal variation and to determine rates of reinvasion. Ants were monitored using pitfalls and food lures. Interspecific competition was determined by applying placebo bait. Results indicate that different management methods did not impact resident ants when they are at low and medium densities and that S. invicta is greatly affected; at high native ant density, competition for these baits is observed affecting both natives and S. invicta. Reinvasion of S. invicta was reduced in areas of low and medium native ant densities previously treated with baits and native ant abundance increased by ~25%. At high native ant densities, reinvasion of S. invicta was similar to Control sites. I conclude: 1) properly used, baits can help in recovery of native ant species that then compete with S. invicta; however, rote re-treatments may have a negative impact on restored populations. 2) “bait failures” may be due to interspecific competition when initial native ant densities are high. Preliminary management considerations and recommendations are presented.

Ants are capable of building close associations with plants, insects, fungi and bacteria. Symbionts can provide essential nutrients to their insect host, however, the development of new molecular tools has allowed the discovery of new microorganisms that manipulate insect reproduction, development and even provide defense against parasitoids and pathogens. In this study we investigated the presence of bacteria inside the Red Imported Fire Ant midgut using molecular tools and transmission electron microscopy. The midgut bacteria were also characterized by their morphology, biochemical activity, and antibiotic resistance profile. After isolation, culture, and characterization of these bacteria, the molecular analysis revealed ten unique profiles which were identified to at least the genus level, Enterococcus sp./durans, Klebsiella ornithinolytica, Kluyvera cryocrescens, Lactococ-cus garvieae, Pseudomonas aeruginosa, Achromobacter xylosoxidans, Bacillus pumilus, Listeria innucua, Serratia marcescens, and an uncultured bacterium from the Entero-bacteriaceae. New SEM and TEM techniques revealed a possible functional association of endosymbiotic bacteria with the insect host, and it also showed the absence of bacteriocytes in the epithelial cells of the midgut. The PCR results, from the bacteria abundance and distribution studies, showed that Enterococcus sp., Kluyvera cryocres-cens and Lactococcus garvieae are the most abundant species, but they are not consistently found in all sites throughout the southeastern United States. Kluyvera cryocrescens, Serratia marcescens, and an uncultured bacterium (isolate #38: Enterobacteriaceae) were genetically modified with the plasmid vector pZeoDsRed and successfully reintroduced into fire ant colonies. Strong fluorescence of DsRed was detected up to seven days after introduction. The transformed bacteria can still be rescued after pupal emergence; however most were passed out in the meconium. We further demonstrated that nurses contributed to the spread of the transformed bacteria within the colony by feeding the meconium to naive larvae. Although the role of midgut bacteria in the fire ant is still unknown, we have no indication that they cause any pathology. Studies emphasizing the role of these bacteria in fire ant physiology are still ongoing. These results are the foundation for a fire ant biological control program using endosymbiotic bacteria as vectors to introduce foreign genes that express proteins with insecticidal properties.

I examined the impacts of the invasive red imported fire ant (RIFA, Solenopsis invicta) on native ants (Monomorium minimum, Paratrechina sp., S. krockowi, Pheidole metallescens, Forelius pruinosus, and Camponotus americanus) and litter removal in a post oak savannah community in central Texas. The study site was divided into 3 adjacent areas, and ant-toxic bait was used, along with additional colonies of RIFA, to establish 3 different densities of RIFA (naturally occurring, low, and high). I surveyed the ants in the 3 density areas and calculated the catch per unit effort for each species. Litter baits were placed in the 3 density areas for 14 12-hour trials. The masses of the litter removed were measured, and means were calculated for each speciesdensity/ trial/date/period/bait combination. The average amounts of litter removed by RIFA and native ant were different in the 3 density areas (0.42 g, 0.0 g, and 0.75 g for RIFA in the natural RIFA density area, low RIFA density area, and high RIFA density area, respectively; 0.0 g, 0.16 g, and 0.15 g for native ants in the natural RIFA density area, low RIFA density area, and high RIFA density area, respectively), indicating that RIFA does have an effect on native ant habitat use.