Integrated pest management concepts for red imported fire ants Solenopsis invicta (Hymenoptera: Formicidae)

Management of imported fire ant species has evolved since their accidental introduction into the United States and currently uses integrated pest management concepts to design, implement, and evaluate suppression programs. Although eradication is the management goal in certain isolated infestation sites, localized goals vary dramatically in larger infestations where reinvasion of treated areas is likely. These goals are influenced by regulatory policies, medical liabilities, ecological impact, and/or economic considerations. Tactics employed in fire ant management programs presented here include cultural and biological control options along with judicious use of site‐specific insecticide products. In addition, program design considerations that include management goal(s), action level(s), ant form (monogyne or polygyne), presence of nontarget ant species, size of treatment area, seasonality, implementation cost, and environmental impact are also presented. Optimally, elegant IPM programs are target specific, threshold driven, environmentally friendly and cost‐effective.     

广东省草皮种植场和城市草坪红火蚁发生为害程度调查

[背景]在防控红火蚁的工作中,有效控制该虫传播途径、降低传播风险是预防的关键。随草皮调运传播是红火蚁扩散的重要方式之一。[方法]采用活蚁巢密度、诱集比率、诱集工蚁数量、发生率等多个指标,调查评价了广东省主要草皮种植地区广州石基、广州增城、深圳南山、惠州博罗等草皮种植场和城市绿化草坪红火蚁发生程度。[结果]广东省草皮种植场红火蚁发生普遍,携带该虫扩散传播的风险极大。不同地区草皮种植场红火蚁发生程度存在明显差异。惠州博罗草场红火蚁发生程度最重,活蚁巢密度、诱集比率、诱集工蚁数量和发生率分别为0．0085个·m^-2、56．75％、16．80头·个^-1和83．60％;深圳南山发生程度最轻,各项指标分别为0．0011个·m^-2、9．62％、0．92头·个^-1和24．50％。城市绿化草坪红火蚁发生较为普遍。调查的3个城市中惠州发生程度最重,活蚁巢密度、诱集比率、诱集工蚁数量和发生率等均最高,分别为0．0149个·m2、10．46％、14．30头·个-1和62．86％。不同品种草坪草红火蚁发生程度不同,以假俭草最高,以上4个指标分别为0．0140个·100m^-2、6．85％、5．57头·个^-1和51．43％。城区类型不同红火蚁发生程度不同,老城区红火蚁发生较轻,新城区较重,发生点常在移植草坪、绿化苗木区域。[结论与意义[广东省主要草皮种植区和城市草坪红火蚁发生均较为普遍,运输携带该虫传播的风险极大,研究结果可为加强草皮检疫、防止携带红火蚁传播提供依据。     

Ethyl formate fumigation for the disinfestation of red imported fire ants Solenopsis invicta Buren

The red imported fire ant, Solenopsis invicta Buren, is a serious invasive pest of quarantine significance. Potential establishment of this ant is of great concern in S. invicta free countries such as South Korea, where there have been multiple recent interceptions. The majority of those detections have been concentrated around main port areas of imported common trade containers, suggesting that disinfestation of the containers, in addition to inspection and disinfestation of containers with agricultural commodities, is necessary for the prevention of S. invicta introduction. So far, however, no regulations and protocols are in place for inspection, detection, and disinfestation of S. invicta in such containers. As a first step toward supporting such regulation, we investigated whether S. invicta could be effectively controlled using ethyl formate, a methyl bromide alternative. Ethyl formate fumigation treatment was effective in controlling 99.9% of S. invicta workers and female alates at 46.1 and 37.7 g h m⁻³ at 13 °C and 23 °C respectively. Our results provide evidence to support its use to disinfest S. invicta in containers. We discuss additional factors that need to be considered to develop disinfestation protocols for S. invicta in commerce shipping containers.     

The nature of Thelohania solenopsae (Microsporidia) cysts in abdomens of red imported fire ants, Solenopsis invicta

Sixty four percent of Solenopsis invicta workers infected with Thelohania solenopsis contained 1-6 "cysts" ranging from 70 to 260 microm in diameter. Light and electron microscope analyses showed that cysts are hypertrophied adipocytes transformed by the parasites, each cyst presumably forming from a single cell. In the first step of the pathogenesis, Nosema-like spores functioning in autoinfection are produced; a diplokaryotic sequence leading to their formation causes fat body hypertrophy. When meiosis occurs, it switches parasite development to production of octospores and/or megaspores. Adipocytes become 2-4xlarger than normal in conjunction with intensive parasite multiplication and octospore maturation. Infected cells eventually lose their cellular organization and are converted into reservoirs for spores. There were no manifestations of cellular immunity, such as encapsulation or nodule formation. Similarly, there were no signs of specialized host-parasite interaction that might be interpreted as xenoma-like complexes. The role of the cysts in the parasite's life cycle is unclear. They may represent a defensive reaction of the host sacrificing the infected cells to segregate the infection. Alternatively, the cyst may help protect spores from environmental hazards and provide a concentrated infectious dose to aid horizontal transmission of the microsporidium. We propose to refer to hypertrophied adipocytes filled with T. solenospsae spores as "sporocytosacs", not "cysts."     

Decreased small mammal and on-host tick abundance in association with invasive red imported fire ants (Solenopsis invicta)

Invasive species may impact pathogen transmission by altering the distributions and interactions among native vertebrate reservoir hosts and arthropod vectors. Here, we examined the direct and indirect effects of the red imported fire ant (Solenopsis invicta) on the native tick, small mammal and pathogen community in southeast Texas. Using a replicated large-scale field manipulation study, we show that small mammals were more abundant on treatment plots where S. invicta populations were experimentally reduced. Our analysis of ticks on small mammal hosts demonstrated a threefold increase in the ticks caught per unit effort on treatment relative to control plots, and elevated tick loads (a 27-fold increase) on one common rodent species. We detected only one known human pathogen (Rickettsia parkeri), present in 1.4% of larvae and 6.7% of nymph on-host Amblyomma maculatum samples but with no significant difference between treatment and control plots. Given that host and vector population dynamics are key drivers of pathogen transmission, the reduced small mammal and tick abundance associated with S. invicta may alter pathogen transmission dynamics over broader spatial scales.     

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.     

Evidence of social facilitation and inhibition in digging behavior of red imported fire ants,Solenopsis invicta

Dear Editor:Except during few events in their life cycles,such as nuptial swarm and mass migration,red imported fire ants,Solenopsis invicta Buren,avoid being exposed to the open air by living in a unique nest system.The nest provides the colony with a controlled environment and an abundance of foraging tunnels,critical for the survival of an ant colony by reducing the risk of desiccation and predation.     

Pathogenicity of individual isolates of entomopathogenic fungi affects feeding preference of red imported fire ants Solenopsis invicta

Seven isolates of entomopathogenic fungi, Isaria fumosorosea (IFCF-H and IFCF-L), Beauveria bassiana s.l. (Bb02 and Bb04) and Metarhizium anisopliae s.l. (Ma01, SM076 and M09), were selected for their pathogenicity against Solenopsis invicta as well as feeding preference of S. invicta. When ants were treated with a conidial suspension at a concentration of 1 × 10⁸ conidia/ml, the median lethal times (LT₅₀) of IFCF-H, IFCF-L, Bb02, Bb04, Ma01, SM076 and M09 were 3.4, 162.6, 7.3, 2.8, 3.8, 7.3 and 2.7 days, respectively, after 10 days. The median lethal concentrations (LC₅₀) on the 10th day after inoculation were 1.20 × 10⁷, 1.56 × 10¹⁰, 4.23 × 10⁷, 3.04 × 10⁶, 6.13 × 10⁶, 2.90 × 10⁷ and 9.90 × 10⁵ conidia/ml, respectively. Furthermore, S. invicta consumed significantly less solution flavoured with Bb04 conidia than the control, which was demonstrated by the lowest preference index (PREF = 0.09). S. invicta did not have a significant feeding preference for other fungal isolates. The pathogenicity (LC₅₀) of fungal isolates was not significantly correlated (R² = 0.013) with the PREF of S. invicta. However, in the paired-choice experiments between different virulent isolates belonging to the same genera, S. invicta tended to select the solution flavoured with conidia of relatively lower pathogenic isolates such as IFCF-L, Bb02 and SM076. We conclude that the pathogenicity of congeneric fungi may affect the feeding preference of S. invicta. Red imported fire ants might adjust their feeding response to entomopathogenic fungi based on the profile of microbial volatile organic compounds.     

Comparative effectiveness of light-microscopic techniques and PCR in detecting Thelohania solenopsae (Microsporidia) infections in red imported fire ants (Solenopsis invicta)

The main goal of this study was to compare the effectiveness of three staining techniques (calcofluor white M2R, Giemsa and modified trichrome), and the polymerase chain reaction (PCR) in detecting the microsporidium Thelohania solenopsae in red imported fire ants (Solenopsis invicta). The effect of the number of ants in a sample on the sensitivity of the staining techniques and the PCR, and the effect of three DNA extraction protocols on the sensitivity of PCR were also examined. In the first protocol, the ants were macerated and the crude homogenate was used immediately in the PCR. In the second protocol, the homogenate was placed on a special membrane (FTA card) that traps DNA, which is subsequently used in the PCR. In the third protocol, the DNA was purified from the homogenate by traditional phenol-chloroform extraction. Except for PCR using FTA cards, the sensitivity (number of samples positive for T. solenopsae) of all detection techniques increased with the number of ants in the sample. Overall, Giemsa was the least sensitive of all detection techniques. Calcofluor was more sensitive than modified trichrome with ants from one site and was equally as sensitive as PCR with crude DNA or a FTA card with ants from both sites. Trichrome staining was equally as sensitive as PCR with a FTA card at both sites, but it was less sensitive than PCR with crude DNA at one site. PCR on FTA cards was less sensitive than PCR with crude DNA for ants from one site but not the other. There was no difference whether crude or phenol-chloroform purified DNA was used as template. In summary, the results of this study show that PCR based on a crude DNA solution is equal to or more sensitive in detecting T. solenopsae than the other detection techniques investigated, and that it can be used as a reliable diagnostic tool for screening field samples of S. invicta for T. solenopsae. Nevertheless, ant smear stained with calcofluor or modified trichrome should be used to buttress findings from PCR.     

广东吴川红火蚁消长规律

采用系统调查的方法研究广东吴川红火蚁Solenopsis invicta Buren蚁巢数量、蚁丘体积和工蚁的年度变化规律,结果表明1年之中红火蚁活动蚁巢密度出现2个高峰期,分别在6~8月和10~12月;4~7月和10~11月新增活动蚁巢数量较大;蚁巢自然消亡出现在多个时间,其中以9月最多。4~11月红火蚁工蚁活动旺盛,用诱饵诱集法监测,5、6月和10、11月红火蚁工蚁出现2个明显盛期,而陷阱法中工蚁数量为单峰型,高峰出现在7月。2种监测方法获得的工蚁数量间相关系数为0.88,达到极显著相关。气温、地表温度、5cm土壤温度与2种方法获得的工蚁数量间相关系数分别为0.88,0.88,0.86和0.93,0.94,0.95,均达极显著水平。红火蚁蚁丘体积4~6月、9~12月增大幅度较大,其中6月份蚁巢增长最为明显。     

红火蚁不同品级个体的药剂敏感性研究

【目的】红火蚁Solenopsis invicta Buren不同品级的个体在群体生存中担负不同的功能。然而,红火蚁群体中不同品级个体的药剂敏感性还不清楚。【方法】本文采用点滴法测定了氟虫腈、高效氯氰菊酯和茚虫威三类不同药剂对红火蚁各品级个体的触杀毒力,以了解其药剂敏感性。【结果】研究结果显示,红火蚁对不同药剂的敏感性存在显著差异,对氟虫腈最为敏感,高效氯氰菊酯次之,而对茚虫威的敏感性最低,但不同品级个体的药剂敏感性规律却基本一致。有翅雌蚁、有翅雄蚁和蚁后的药剂敏感性最高,3个品级个体的药剂敏感性没有显著差异;除高效氯氰菊酯外,兵蚁的敏感性显著低于有翅蚁和蚁后,而工蚁又显著低于兵蚁。4龄幼蚁对供试的3种杀虫剂的敏感性非常低,致死中量分别为428.77 mg/kg、699.77 mg/kg和1 159.95 mg/kg,比对有翅雌蚁的致死中量高数百至数千倍。对毒力线斜率值的分析发现,同一品级内个体间对不同药剂的敏感性也存在显著差异,对氟虫腈的敏感性表现出品级内个体较大差异,特别是兵蚁和工蚁的敏感性差异最大,其斜率值分别为1.1和1.8,而对茚虫威的个体敏感性差异极小,其斜率值均≥4.7,且工蚁个体间表现出最高的同质性,其斜率值达7.8。【结论】同一品级的个体对不同药剂的敏感性差异没有一致规律,但基本上表现出个体差异较小的特点,特别是4龄幼蚁、有翅雄蚁和蚁后3个品级内个体的药剂敏感性差异较小,其斜率值均≥4.0。本研究的结果为田间防治红火蚁化学药剂的合理使用提供理论指导。     

我国大陆红火蚁入侵扩张趋势长期预测

红火蚁Solenopsis invicta Buren是一种严重危害农林业生产、生命健康、公共安全和生态环境的国际性重大外来入侵害虫。2004年9月中国大陆首次发现红火蚁,2021年12月该蚁已入侵了12个省区近500个县区。本研究根据中国大陆红火蚁入侵发生县区数量变化,结合潜在适生区域评价信息,建立了红火蚁入侵县区数量与入侵时间长度间关系模型,并对入侵县区数量变化趋势作出长期预测。当中国大陆红火蚁潜在入侵县区数量上限分别为1 400、1 500和1 600个时,入侵县区数量与入侵时间长度关系模型分别为N=1400/(1+e^{5.4048-0.1784T})、N=1500/(1+e^{5.4335-0.1757T})和N=1600/(1+e^{5.464-0.1734T})。基于以上模型的分析结果显示,我国红火蚁快速扩散传播从2009-2010年开始,快速扩张期可能持续26～28年,年平均新增县区41～52个/年,预测2035-2037年入侵县区数量增长速率将开始减缓,2...     

Sampling efficacy for the red imported fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Cost-effective detection of invasive ant colonies before establishment in new ranges is imperative for the protection of national borders and reducing their global impact. We examined the sampling efficiency of food-baits and pitfall traps (baited and nonbaited) in detecting isolated red imported fire ant (Solenopsis invicta Buren) nests in multiple environments in Gainesville, FL. Fire ants demonstrated a significantly higher preference for a mixed protein food type (hotdog or ground meat combined with sweet peanut butter) than for the sugar or water baits offered. Foraging distance success was a function of colony size, detection trap used, and surveillance duration. Colony gyne number did not influence detection success. Workers from small nests (0- to 15-cm mound diameter) traveled no >3 m to a food source, whereas large colonies (>30-cm mound diameter) traveled up to 17 m. Baited pitfall traps performed best at detecting incipient ant colonies followed by nonbaited pitfall traps then food baits, whereas food baits performed well when trying to detect large colonies. These results were used to create an interactive model in Microsoft Excel, whereby surveillance managers can alter trap type, density, and duration parameters to estimate the probability of detecting specified or unknown S. invicta colony sizes. This model will support decision makers who need to balance the sampling cost and risk of failure to detect fire ant colonies.     

Selective male mortality in the red imported fire ant, Solenopsis invicta

Males in polygyne populations of Solenopsis invicta are primarily sterile diploids and thought to not express the Gp-9 gene coding for a pheromone-binding protein affecting complex social behavior. We examined an aspect of the breeding system hitherto not considered--male Gp-9 genotypes in relation to sperm stored in queens. Four sites with varying frequencies of sympatric monogyne and polygyne colonies were sampled, including sexuals, workers, and broods from four colonies. Most queens were heterozygotes storing B sperm. Although predicted to be common, only 14 of 504 males were B or BB genotypes, suggesting strong selection. Increased frequency of polygyne colonies at each site paralleled increases in queens with b sperm (1.9-32.8%) and of noninseminated queens. The presence of both B and b sperm in 1.9-18.9% of queens, genotype profiles of colonies, and genotypes of offspring from individual queens suggest some frequency of multiple mating. The bb genotype, rather than an obligate, developmental lethal, was present in some queens and common in alates, workers, and brood. Selective mortality of sexuals may affect multiple aspects of the breeding system, including female-mediated dispersal, mating success, and gene flow.     

热处理对红火蚁工蚁的致死效果评估

热处理作为一种无污染、无残留、环境友好型防治措施,在红火蚁Solenopsis invicta Buren（Hymenoptera：Formicidae）防控中具有广阔的应用前景。然而,目前有关热处理对红火蚁防治效果的研究相对较少,致死温度和致死时间的最佳组合仍值得进一步探究。为此,本研究在实验室条件下,采用干热（45.5、46、46.5、47、47.5、48、49、50和51℃）和热水（41、41.5、42.5、43、45、46、47和48℃）处理红火蚁工蚁0.5~5 min,记录工蚁的击倒率、及处理后12 h的存活情况。结果显示,热处理温度越高、时间越长,红火蚁工蚁的击倒率和死亡率越高。干热处理过程中,48℃高温处理4 min、49℃高温处理3 min、50或51℃高温处理2 min均可杀死100%的工蚁。采用热水处理时,45或46℃热水处理5 min、48℃热水处理2 min便可杀死全部的工蚁。因此,作为一种安全、高效的物理防治措施,热处理可用于红火蚁的有效防控。     

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。     

Detection of magnetism in the red imported fire ant (Solenopsis invicta) using magnetic resonance imaging

Red imported fire ant (Solenopsis invicta) workers, queens, and alates were analyzed by magnetic resonance imaging (MRI) for the presence of natural magnetism. Images of ants showed distortion patterns similar to those of honey bees and monarch butterflies, both of which possess ferromagnetic material. The bipolar ring patterns of MRI indicated the presence in fire ants of small amounts of internal magnetic material, which may be used in orientation behaviors, as in the honey bees. Bioelectromagnetics 18:396–399, 1997. © 1997 Wiley-Liss, Inc.     

Genome complexity and organization in the red imported fire ant Solenopsis invicta Buren

The red imported fire ant Solenopsis invicta is the most destructive invading arthropod in the southern United States, yet little is known about its genome complexity and organization. Here we report the size, organization and GC content of S. invicta genome. DNA reassociation kinetics using S1 nuclease assay and a modified second-order kinetics model indicated that the S. invicta genome is approximately 0.62 picograms or 5.91 x 10(8) base pairs, composed of 36% unique, 41% moderately repetitive and 23% highly repetitive/foldback sequences. Comparison of the reassociation kinetics of short and long DNA fragments revealed that the sequence arrangement follows a pattern of short period interspersion, as in most organisms with relatively large genomes. Melting-temperature analysis showed that the GC content of the fire ant genomic DNA is 34.8%, similar to that of most eukaryotic organisms. The results reveal that the fire ant genome is much larger and more complex than those of a number of hymenopteran insects studied to date. Our study provides a foundation for further analysis and genetic manipulation of the S. invicta genome.     

Establishing guidelines to improve identification of fire ants Solenopsis xyloni and Solenopsis invicta

As red imported fire ant, Solenopsis invicta Buren, continues to expand its range into the southwestern United States, it can be easily confused with the native southern fire ant, Solenopsis xyloni McCook. Variability in the morphological characteristics commonly used to differentiate these ant species was quantified by examining the length of the clypeal tooth, striations of the mesopleuron, length of antennal scape, area of the petiolar process, number and size of mandibular teeth, and color by using both scanning electron and light microscopy. Given enough samples, the average values of each of these characteristics is different between the two species; however, significant morphological variability occurs in both S. xyloni and S. invicta populations, creating an area of overlap where either of the two species could exhibit similar characteristics. Better differentiation of these two species is achieved using a combination of characteristics, but morphological techniques are not dependable unless numerous ants from each population are analyzed by a taxonomist familiar with Solenopsis. For situations requiring a more accurate identification, such as before quarantining a county or a portion of a county, a molecular technique using mitochondrial DNA and polymerase chain reaction techniques was developed.