Infection characteristics of Solenopsis invicta virus 2 in the red imported fire ant, Solenopsis invicta

Solenopsis invicta virus 2 (SINV-2) is the second virus identified from the fire ant, S. invicta Buren. SINV-2 is unique among positive-strand RNA viruses from insects by possessing four cistrons in a monopartite genome. Fire ant colonies testing positive for SINV-2 by RT-PCR did not exhibit any discernable symptoms. RT-PCR-based surveys for SINV-2 among 688 fire ant mounds in Alachua County, Florida, sampled during the period January, 2006 through December, 2007 showed that the prevalence of SINV-2 among nests ranged from 1.6% to 16.4%. Unlike S. invicta virus 1, no seasonal-associated prevalence was observed with regard to SINV-2 infection among fire ant colonies. No social form specificity was evident; SINV-2 was found in both monogyne and polygyne S. invicta ants. Real-time quantitative PCR experiments showed that SINV-2 genome equivalents per individual ant ranged from 1.9 × 10⁷ in. pupae to 4.3 × 10¹¹ in. inseminated queens. The SINV-2 infection was detected in all ant stages examined (eggs, larvae, pupae, workers, and queens). Tissue tropism studies indicated that the alimentary canal (specifically the midgut) is most likely the susceptible tissue. SINV-2 was successfully transmitted to uninfected S. invicta ants by feeding a partially purified homogenate of SINV-2-infected ants. The SINV-2 transmission rate ranged from 30% to 80%, and both positive (genomic) and negative (replicative) SINV-2 RNA strands accumulated in recipient ants over the course of the experiment. These results indicated that SINV-2 replicates within S. invicta.     

Expressed sequence tags from the red imported fire ant, Solenopsis invicta: annotation and utilization for discovery of viruses

An expression library was created and 2304 clones sequenced from a monogyne colony of Solenopsis invicta. The primary intention of the project was to utilize homologous gene identification to facilitate discovery of viruses infecting this ant pest that could potentially be used in pest management. Additional genes were identified from the ant host and associated pathogens that serve as an important resource for studying these organisms. After assembly and removal of mitochondrial and poor quality sequences, 1054 unique sequences were yielded and deposited into the GenBank database under Accession Nos. EH412746 through EH413799. At least nine expressed sequence tags (ESTs) were identified as possessing microsatellite motifs and 15 ESTs exhibited significant homology with microsporidian genes. These sequences most likely originated from Thelohania solenopsae, a well-characterized microsporidian that infects S. invicta. Six ESTs exhibited significant homology with single-stranded RNA viruses (3B4, 3F6, 11F1, 12G12, 14D5, and 24C10). Subsequent analysis of these putative viral ESTs revealed that 3B4 was most likely a ribosomal gene of S. invicta, 11F1 was a single-stranded RNA (ssRNA) virus contaminant introduced into the colony from the cricket food source, 12G12 appeared to be a plant-infecting tenuivirus also introduced into the colony as a field contaminant, and 3F6, 14D5, and 24C10 were all from a unique ssRNA virus found to infect S. invicta. The sequencing project illustrates the utility of this method for discovery of viruses and pathogens that may otherwise go undiscovered.     

Culture-independent identification of gut bacteria in fourth-instar red imported fire ant, Solenopsis invicta Buren, larvae

Red imported fire ants (RIFA), Solenopsis invicta Buren, are medical, urban, and agricultural pests from South America. They are successful invaders due to their preference for disturbed habitats, high reproductive rates, and the ability to feed on a wide variety of food items (omnivorous). Fourth-instar larvae are used by the colony to digest solid food and then regurgitate it for consumption by workers and queens. Larvae are an ideal source of investigations of endosymbiotic bacteria possibly involved in nutrient distributions. Our study utilized 16S rDNA sequencing to describe the composition of the bacterial community in fourth-instar ant larvae in order to identify possible endosymbiotic bacteria present therein. The 16S rRNA gene was directly amplified from mixed-population DNA of whole fire ant larval guts and cloned into Escherichia coli. Bacterial communities from three geographically separated RIFA colonies were examined. Sequenced bacterial clones from guts were determined to be predominantly from the phylum Proteobacteria and the family Enterobacteriaceae. Our results did not detect the presence of endosymbiotic bacteria in the guts of RIFA larvae among the colonies. In addition, minimal species overlap was found when bacterial inventories were compared among colonies. Thus, bacteria coadapted with red imported fire ant larvae were not detected. Identified bacteria were not closely affiliated with endosymbiotic bacteria common in other insect species. Bacteria communities appeared to be unique to each geographical location and were determined by the foods consumed by the ants.     

Defensiveness of the fire ant, Solenopsis invicta, is increased during colony rafting

Colonies of the fire ant, Solenopsis invicta, can survive flood conditions by forming a raft of ants that floats on the water’s surface until the flood recedes or higher ground is found. Having been forced from the protection of their subterranean nests, rafting colonies are totally exposed and are without retreat. I tested the hypothesis that rafting S. invicta colonies would compensate for their elevated vulnerability by increasing their defensiveness. I measured defensiveness using the amount of venom workers delivered per sting (venom dose), since the repellent effects (i.e., pain and tissue damage) of fire-ant venom are dose-dependent. In the laboratory I assayed colony defensiveness before and after flooding colonies from their nests with water. Colonies were consistently and significantly more defensive while rafting (i.e., each colony’s workers delivered higher venom doses when their colony was rafting than they did when it was assayed pre-flood). The larger venom doses of rafting colonies may reduce their chances of being damaged by encounters with other animals by reducing the duration of such encounters through increased repellency. Encounters with S. invicta during flood conditions have the potential to be unusually dangerous; large concentrations of workers are exposed and available for defense, and they deliver significantly larger venom doses when they sting. Received 29 March 2005; revised 20 June 2005; accepted 24 June 2005.     

Isolation, characterization, and molecular identification of bacteria from the red imported fire ant (Solenopsis invicta) midgut

Bacteria were isolated and cultured from the red imported fire ant (Solenopsis invicta) midgut. The small-subunit ribosomal RNA gene, (16s rRNA gene, approximately 1500 bp) was amplified from bacterial genomic DNA using the polymerase chain reaction and consensus sequence primers. Restriction fragment length polymorphism analysis revealed 10 unique profiles, indicating that at least 10 different bacteria are present in red imported fire ant midguts. The 16s rRNA gene sequence was determined for these isolates and queried against the NCBI genetic database. The results identified all isolates to at least the genus level. Antibiotic resistance profiles and biochemical activities were also determined for these species. This work provides the basis for a wider characterization of bacterial distributions in fire ant colonies and provides strains suitable for genetic manipulation to develop novel methods of fire ant control.     

Solenopsis invicta virus-1 tissue tropism and intra-colony infection rate in the red imported fire ant: a quantitative PCR-based study

Quantitative real-time PCR was employed to measure the Solenopsis invicta virus 1 (SINV-1) load in tissues, individuals, and among colonies of the red imported fire ant, S. invicta Buren. Among tissues examined from SINV-1-infected adults and larvae, the alimentary canal (specifically the midgut) consistently had the highest number of SINV-1 genome copies (91.1 and 99.9%, respectively). Negative staining of a supernatant of the gut homogenate demonstrated the presence of spherical virus particles with a diameter of 30-35 nm, consistent with SINV-1. The number of SINV-1 genome copies in infected larvae and workers from the same queenright colonies were similar to each other. In other words, the infection rate was consistent among both developmental stages. No significant differences were observed in SINV-1 genome copy number among infected colonies sampled during the winter and summer. Although the SINV-1 infection rate of summer-collected mounds was previously shown to be six-times higher than winter-collected mounds, the intra-colony infection rate appears to be unaffected by season. Perhaps less inter-mound interaction during the winter months among S. invicta restricts spread of the virus. A positive correlation between intra-colony infection rate and mean SINV-1 genome copy number per ant was also observed. Based on these results, it is likely that SINV-1 replicates in gut epithelia of S. invicta and virus is shed into the gut lumen where it may be transmitted to nestmates by trophallaxis.     

Identification and action of juvenile hormone III from sexually mature alate females of the red imported fire ant,Solenopsis invicta

Analysis of extracts of hemolymph obtained from sexually mature alate females of Solenopsis invicta from monogyne colonies resulted in identification of juvenile hormone III (JH III). The average amount of JH III was 0.32±0.04 pmol/μmolof hemolymph. Topical application of 0.038 pmol of JH III was sufficient to stimulate alates to shed their wings in the presence of the queen. The time in which alates were induced to dealate decreased linearly with increasing concentrations of JH III from 0.038 to 3.8 pmol. However, higher JH III concentrations deviated from linearity and did not reach dealation times comparable with those that occur after mating flights. Thus, it appears that the mechanism of dealation that occurs when female alates are out of the influence of their queen is different from the one associated with mating flights. Application of 0.42 μmol of precocene II inhibited dealation of alates in queenless colonies. However, this inhibition was reversed after applying 38 pmol JH III to precocene-treated alates. The sizes of corpora allata (CA) from sexuals treated with JH III did not differ from those of controls. However, the sizes of CA were reduced in alates treated with precocene II. The results indicated that JH was important to dealation.     

几种饵料对红火蚁觅食的引诱作用

在荒地类型生境中测定花生酱、猫饲料、狗饲料、花生油、面包及蜂蜜等几种常见饵料对红火蚁的引诱作用。结果表明:面包、狗饲料、猫饲料和花生酱对红火蚁引诱力较强,花生油次之,蜂蜜最低;选择性试验结果表明红火蚁对供试的几种饵料无明显选择性。     

介绍红火蚁的野外采集和实验室饲养的方法

介绍了红火蚁Solenopsis invictaBuren的田间采集、蚁群分离和实验室饲养和操作方法及红火蚁人工饲料的制备,结合实验室饲养经验描述了日常红火蚁饲养所需设备和器具,简述红火蚁饲养的关键技术和注意事项。为开展红火蚁的生物学、生态学和药剂筛选提供切实可行的方法。     

带土园艺植物传播红火蚁的风险调查

调查了广东广州、深圳40余个苗木花卉场74种带土园艺植物上红火蚁Solenopsis invicta Buren发生情况。调查结果表明,桉树苗、海枣、垂叶榕、黄金香柳、小叶榕、狗尾草、罗汉松等17种植物上红火蚁发生比率超过1%,是高风险带土植物。不同生产环境、不同栽培方式中盆/钵/袋栽红火蚁发生高于地面栽培方式,露天置于砂土、泥土、碎石上红火蚁发生风险较高,置于水泥地上的风险较低。提出了降低带土园艺植物传播红火蚁的管理措施。     

Source of alate excitant pheromones in the red imported fire antSolenopsis invicta (Hymenoptera: Formicidae)

At the onset of mating flights inSolenopsis invicta, workers swarm excitedly over the mound as alates prepare to fly. Previous studies demonstrated that this excitement is stimulated by the male and female alates. We investigated the glandular source(s) of pheromones produced by the alates that cause excitement. The only common female and male alate body part that elicited excitement when crushed was the head. Within the head, excised mandibular glands were found to be responsible for worker excitement. Fire ant workers are very sensitive to external stimuli and some excitement was elicited by crushed female gasters and male thoraces, but the response was never as significant as with crushed heads. Tests with summer and winter alates revealed similar results, except that gasters of winter female alates had a greater excitant effect than did gasters of summer female alates. This may be due to the production of attractant pheromones by the poison glands of overwintering female alates. We conclude that the mandibular gland is the source of alate excitant pheromones.     

研究红火蚁工蚁活动性的新方法-刻度图示法

应用一种新方法--刻度图示法研究红火蚁工蚁Solenopsis invicta Buren群体活动性规律,结果表明,标尺上红火蚁最高爬升高度、平均爬升高度、工蚁恢复平静时间、工蚁累计数量均随着蚁巢体积增大而增大,通过分析建立红火蚁工蚁活动性程度各指标值与蚁巢大小关系多个模型.     

蚁丘被破坏程度对红火蚁蚁群迁移的影响

本文调查研究了蚁丘被破坏的程度对红火蚁Solenopsis invicta Buren蚁群迁移的影响。结果表明,蚁巢地表部分被破坏可导致红火蚁蚁群发生分巢、搬巢等现象,蚁群的移巢比率随着蚁丘被破坏程度的增大而增大。当蚁丘体积被破坏75%时分巢比率最高,为14.44%;被破坏100%时搬巢比率、移巢比率均最高,分别为16.27%、27.00%。红火蚁蚁丘被破坏程度(D)与蚁群迁移比率(M)之间关系模型为M=4.3443+25.474D-3.4857D2。蚁丘受到破坏后,蚁群迁移距离平均为4.3m,迁移方向是随机的。     

Characteristics of 11 polymorphic microsatellite markers in the red imported fire ant, Solenopsis invicta Buren

We have characterized 11 polymorphic microsatellite loci in the invasive ant Solenopsis invicta. Primer pairs were evaluated on fire ants collected from monogyne mounds in Lauderdale County, Mississippi. The observed and effective number of alleles ranged from two to six and from 1.31 to 2.64, respectively. The observed and expected heterozygosity values ranged from 0.1613 to 0.7826 and from 0.1491 to 0.6242, respectively. The polymorphism information content of the microsatellites ranged from 0.1482 to 0.6208. Probability tests indicated significant deviations from the Hardy-Weinberg equilibrium at three loci. Pairwise tests did not detect linkage disequilibrium between any pair of loci.     

Population genetic structure of the red imported fire ant, <Emphasis Type="Italic">Solenopsis invicta</Emphasis>, in Taiwan

We generated and analyzed microsatellite genotypic data and mtDNA sequence data from the fire ant Solenopsis invicta collected from two separate infested areas (Taoyuan and Chiayi) in Taiwan to infer the population and colony structure of these recently established populations. These genetic analyses revealed the following patterns: 1) Relatedness among worker nestmates was significantly greater than zero for both social forms from both populations; 2) No significant isolation by distance was found among nests within each social form from either population; 3) Significant mtDNA but no nuclear differentiation occurs between sympatric social forms in Taoyuan; 4) Molecular signatures of genetic bottlenecks associated with recent introductions are evident in both populations; and 5) The two sampled populations, Taoyuan and Chiayi, are highly genetically differentiated at both the nuclear or mtDNA genomes and most likely derive from two separate introductions into Taiwan. While results from these analyses generally were consistent with predictions based on the known biology of these ants and similar studies of S. invicta in the U.S.A. and South America, some patterns likely reflect the recent introduction and human-mediated inadvertent transport of ants in Taiwan. This is the first study to investigate the population and colony structure of fire ants in Taiwan and results from our study represent an important contribution to the ongoing efforts aimed at eradicating this invasive pest in Taiwan. Received 18 June 2007; revised 11 October 2007; accepted 17 October 2007.     

The labial gland system of larvae of the imported fire ant,Solenopsis invicta Buren

Summary The authors describe the ultrastructure of the labial gland system in imported fire ant larvae, Solenopsis invicta Buren and present an enzyme analysis of enzymes in labial-gland secretions and midgut contents. The tubes of the labial gland produce and secrete a proteinaceous substance rich in digestive enzymes. The narrow cells of the reservoir of the gland have little or no secretory function but the lumen stores the proteinaceous secretion. The labial-gland enzymes include proteases and amylases, which function in extraintestinal digestion of solid food placed on the anteroventral body region of 4th-instar larvae by adult workers. The midgut contains proteases, amylases, and upases. Lipids appear to be predigested by the workers before being fed to the larvae.Approved as TA 15262 by the Director of the Texas Agricultural Experiment Station in cooperation with ARS/USDA. Supported by the Texas Department of Agriculure interagency agreement IAC-0487 (78-79)We would like to thank Rosemary Kamas, Dr. John Mirenda, and Mike Strand for their help in dissections of larvae and Dr. Howard Williams for his advice and suggestions     

研究红火蚁工蚁活动性的新方法—刻度图示法

应用一种新方法——刻度图示法研究红火蚁工蚁Solenopsis invicta Buren群体活动性规律,结果表明,标尺上红火蚁最高爬升高度、平均爬升高度、工蚁恢复平静时间、工蚁累计数量均随着蚁巢体积增大而增大,通过分析建立红火蚁工蚁活动性程度各指标值与蚁巢大小关系多个模型。     

氟磺酰胺复配毒饵对红火蚁的田间防治效果

在深圳市龙岗区和宝安区对氟磺酰胺复配毒饵进行药效评价,试验结果表明,施药后3～15d,龙岗实验区蚁巢周围均有死亡工蚁陆续出现。第7d时,0.75%氟磺酰胺复配毒饵防治效果为16.99%,第28d时防治效果达47.43%,在试验结束的第140d时防治效果达97.93%;对照药剂0.5%氟磺酰胺毒饵对红火蚁Solenopsis invicta Buren的防除效果迅速,在第7d防治效果达50%以上。在宝安实验区,蚁巢的防治效果也随施药后时间的延长而增加,第28d的防治效果为51.65%,试验结束时防治效果达到94.72%;对照药剂0.5%氟磺酰胺毒饵42d防治效果达最大值为92.88%。上述结果显示,0.75%氟磺酰胺复配毒饵具有较快压低红火蚁种群密度,持效控制实验区红火蚁种群的特点。     

Sources of spores for the possible horizontal transmission of Thelohania solenopsae (Microspora: Thelohaniidae) in the red imported fire ants, Solenopsis invicta

We screened adult and larval secretions and midden piles for the presence of Thelohania solenopsae spores to decipher potential sources for the horizontal transmission of the pathogen in fire ants. Hemolymph samples from both adult and larvae were also screened to rule out hemolymph contamination of samples. In adults, Thelohania spores were found in the crop and the fecal fluids, although only free spores were found in the fecal fluids of adults. In fourth instar larvae, both free and octospores were seen in midgut and the meconium samples. All of the midden pile samples had T. solenopsae spores of both types. Based on these results, we theorize that the pathogen may be horizontally transmitted within a colony by the removal and sharing of meconium of prepupating fourth instar larvae by adult workers and by the adult fecal droppings, and intercolonially by contamination of midden piles or brood raiding.     

Modelling the potential spread of Solenopsis invicta Buren (Hymenoptera: Formicidae) (red imported fire ant) in Australia

Abstract  Quantifying the potential spread and density of an invading organism enables decision-makers to determine the most appropriate response to incursions. We present two linked models that estimate the spread of Solenopsis invicta Buren (red imported fire ant) in Australia based on limited data gathered after its discovery in Brisbane in 2001. A stochastic cellular automaton determines spread within a location (100 km by 100 km) and this is coupled with a model that simulates human-mediated movement of S. invicta to new locations. In the absence of any control measures, the models predict that S. invicta could cover 763 000–4 066 000 km² by the year 2035 and be found at 200 separate locations around Australia by 2017–2027, depending on the rate of spread. These estimated rates of expansion (assuming no control efforts were in place) are higher than those experienced in the USA in the 1940s during the early invasion phases in that country. Active control efforts and quarantine controls in the USA (including a concerted eradication attempt in the 1960s) may have slowed spread. Further, milder winters, the presence of the polygynous social form, increased trade and human mobility in Australia in 2000s compared with the USA in 1940s could contribute to faster range expansion.