Research on the Control Cover against Solenopsis invicta and Rapid Extinguishment of Its Epidemic

Based on the biological characteristics of Solenopsis invicta and the structural characteristics of its ant nest,a fast and efficient closed treatment device was developed.Compared with the simple chemical treatment commonly used at present,the developed treatment device(the ant nest control cover)is a fast and efficient method to exterminate S.invicta in 7 d,featured by short course,quick results and good effect.

New Evidence for the Hypothesis of Reducing Natural Enemy Pressure of Eupatorium adenophorum: Solenopsis invicta Competing with Doxrylus orientalis to Feed on E. adenophorum

Natural enemy insects are important factors in regulating plant invasion. The interactions between multiple insect species resulting from invasive plants remain poorly understood despite their potential. We observed notorious invasive plants Eupatorium adenophorum Sprengel were competedly fed by Solenopsis invicta Buren (Hymenoptera: Formicidae) and Dorylus orientalis Westwood (Hymenoptera: Formicidae) beside the scientific research base of Kunming University. It was first observed that D. orientalis was eating the epidermis, cortex, phloem and other root and stem tissues of E. adenophorum in soil. Two months later, it was observed that S. invicta ate the epidermis, cortex, phloem and other aboveground stem tissues of E. adenophorum. S. invicta attacked D. orientalis and displaced their living space by causing the later dead, injured, or even disabled. This phenomenon suggested that local herbivorous insects have adapted to E. adenophorum well, which will intensify the naturalization process of E. adenophorum in local habitats. In a homogeneous garden planting experiment of E. adenophorum conducted at the experimental base of Kunming University, the biomass of the introduced (China) populations of E. adenophorum was lower than that of the native (Mexico) populations, although there was no statistically significant difference. These results indicate a possible positive correlation between the increase in natural enemy pressure and the decrease in fitness of E. adenophorum.

Insecticide induction of O-demethylase activity and expression of cytochrome P450 genes in the red imported fire ant (Solenopsis invicta Buren)

The red imported fire ant （Solenopsis invicta） is a global major invasive pest, and has caused significant economic, social and environmental impacts since its invasion to mainland of China in 2004. To date, chemical control has been the most effective measure. However, the long-term use of chemicals would lead to an unexpected rebound. To understand the risks and explore the mechanisms of detoxification or induction to insecticides in S. invicta, the O-demethylase activity and expression of cytochrome P450 genes of workers and queens, and the effects of chlorpyrifos and fipronil exposure in workers were investigated. Biochemical assays showed the O-demethylase activity of cytochrome P450 was significantly higher in workers than in queens （1.66-fold）, and was significantly induced in workers exposed to chlorpyrifos and fipronil, reaching a maximum （3.00- and 1.95-fold） at 48 h and then decreasing dramatically compared to controls （exposed to acetone counter- part）. The relative expression levels of 12 cytochrome P450 expressed sequence tags （ESTs） in workers were significantly higher than in queens （from 2.3- to 36.4-fold）. Multiple cytochrome P450 genes （except 9E4） were co-up-regulated （from 1.5- to 2.86-fold） in workers exposed to fipronil. These results indicated that the increased O-demethylase activity may result from the increased transcription levels of cytochrome P450 related to detoxification of insecticides in S. invicta. It appears that cytochrome P450 plays an important role in enhanced metabolic detoxification of insecticides. At the same time, it also provides the theoretical basis for resistance management and rational usage of insecticides to control S. invicta.

A global study of transcriptome dynamics in the venom gland of Solenopsis invicta Buren during laboratory rearing

Venom plays several important roles in the life of the fire ant,Solenopsis invicta Buren.Laboratory rearing significantly affected the toxin component of S.invicta.However,the molecular mechanism of the change of venomous components when kept in the laboratory is unclear.In this study,RNA sequencing technique(RNA-Seq)was performed to explore differentially expressed genes in the venom gland of S.invicta at 0,10,and 60 days after laboratory rearing.The RNA-Seq results showed that the expression of a large number of genes changed.The DEGs were involved in multiple pathways,including proteolysis,serine-type endopeptidase,and allergen.Furthermore,RNA-Seq and qRT-PCR data revealed that the expression of some genes related to proteolysis and allergen significantly decreased.Thus,our data generated new data relating to toxin-component and the transcriptome dynamics in the venom gland of S.invicta during laboratory rearing.

Control Effects of Three Poisonous Baits on Solenopsis invicta Buren

The field control effects of different concentrations of indoxacarb baits,fipronil baits and chlorfenapyr baits on Solenopsis invicta was evaluated. The results showed that at 21 post administration,the control effects of 0. 04% indoxacarb on nests and worker ants reached 100%; the control effect of 0. 02% and0. 06% indoxacarb on active nests and worker ants were 87. 50% and 100%,respectively; 0. 000 25% and 0. 000 5% fipronil and 0. 05% chlorfenapyr also had significant control effects on active nests and worker ants. At 30 d post administration,the decline rates of ant colony grade treated by 0. 04% and 0. 06% indoxacarb,0. 000 25% fipronil and 0. 05% chlorfenapyr were 100%,100%,91. 44% and 98. 11%,respectively,and the comprehensive control effect reached 97. 18%.

The temporal-spatial expression and functional analysis of three gustatory receptor genes in Solenopsis invicta using sweet and bitter compounds

The insect gustatory system participates in identifying potential food sources and avoiding toxic compounds.During this process,gustatory receptors(GRs)recognize feeding stimulant and deterrent compounds.However,the GRs involved in recognizing stimulant and deterrent compounds in the red imported fire ant,Solenopsis invicta,remain unknown.Therefore,we conducted a study on the genes SinvGR1,SinvGR32b,and SinvGR28a to investigate the roles of GRs in detecting feeding stimulant and deterrent compounds.In this current study,we found that sucrose and fructose are feeding stimulants and the bitter compound quinine is a feeding deterrent.The fire ant workers showed significant behavior changes to avoid the bitter taste in feeding stimulant compounds.Reverse transcription quantitative real-time polymerase chain reaction results from developmental stages showed that the SinvGR1,SinvGR32b,and SinvGR28a genes were highly expressed in fire ant workers.Tissue-specific expression profiles indicated that SinvGR1,SinvGR32b,and SinvGR28a were specifically expressed in the antennae and foreleg tarsi of workers,whereas SinvGR32b gene transcripts were also highly accumulated in the male antennae.Furthermore,the silencing of SinvGRI or SinvGR32b alone and the co-silencing of both genes disrupted worker stimulation and feeding on sucrose and fructose.The results also showed that SinvGR28a is required for avoiding quinine,as workers with knockdown of the SinvGR28a gene failed to avoid and fed on quinine.This study first identified stimulant and deterrent compounds of fire ant workers and then the GRs involved in the taste recognition of these compounds.This study could provide potential target gustatory genes for the control of the fire ant.

Developmental DNA methyltransferase expression in the fire ant Solenopsis invicta

DNA methylation is accomplished in animals by 2 classes of enzymes known as DNA methyltransferases, DNMT3 and DNMT 1, which perform de novo methylation and maintenance methylation, respectively. Several studies of hymenopteran eusocial insects suggest that DNA methylation is capable of influencing developmental plasticity. However, fundamental questions remain about the patterning of DNA methylation during the course of insect development. In this study, we performed quantitative real-time PCR （qPCR） on transcripts from the single-copy orthologs of DNMT1 and DNMT3 in the red imported fire ant, Solenopsis invicta. In particular, we assessed the expression of S. invicta Dnmtl and Dnmt3 mRNA during 7 stages of worker development, among behaviorally distinct adults, and among male and female gonads. Dnmt3 was most highly expressed during embryonic development, whereas Dnmtl was similarly expressed throughout the course of develop- ment. Moreover, Dnmtl and Dnmt3 were highly expressed in testes and ovaries. Neither Dnmt was significantly differentially expressed among heads of behaviorally distinct adult castes. Our results support the hypothesis that extensive patterning of DNA methylation occurs during gametogenesis and embryogenesis in the insect order Hymenoptera.

Potential range expansion of the red imported fire ant(Solenopsis invicta) in China under climate change

The red imported fire ant（RIFA, Solenopsis invicta）, a notorious invasive insect, has received considerable attention owing to its impacts on native biodiversity, agriculture, and human health. Under global warming, the inhabitable area of the RIFA may be enlarged. However, few studies have focused on the potential range expansion of the RIFA in East Asia. Using a process-based physiological model, we simulated the potential range of the RIFA in China based on gridded temperature datasets for the current（2004–2012） and future（2090–2100） climates under Representative Concentration Pathway（RCP） 4.5 and RCP 8.5. It was found that the southeastern part of China（below 32°N） is suitable for RIFA proliferation. The present distribution area of the RIFA corresponds well with the potential range simulated by the model. In the RCP 4.5 and RCP 8.5 warming scenarios, the inhabitable area of the RIFA along the northern boundary would on average extend 101.3±85.7（mean±SD） and 701.2±156.9 km, respectively, by the end of the 21 st century. Therefore, future climate change would significantly affect the inhabitable area of the RIFA. Our results provide the basis for local quarantine officials to curtail accidental introductions of this insect, especially in the certain and possible infestation zones.

Invasion history of Solenopsis invicta （Hymenoptera： Formicidae） in Fujian, China based on mitochondrial DNA and its implications in development of a control strategy

One of the most invasive species worldwide, Solenopsis invicta Buren, has been described in China since 2003. Recent studies have suggested that China populations are the result of introductions from the USA; however, detailed molecular studies need to be performed in order to understand the expansion and potential multiple introductions from other countries into China. As there were populations of red imported fire ant, S. invicta in different areas and with different methods of introduction, mitochondrial cytochrome oxidase Ⅰ gene was used as a marker from 12 populations in four cities in Fujian Province, China, to determine the relationship of invasion among these populations. The three most common haplotypes previously describe in invasive populations of S. invicta： H5, H22 and H36, were found in Fujian. However, frequencies in each city were different. For instance, three populations from Longyan city which invaded with waste plastics, shared haplotype H5. Populations from Xiamen city and Jinjiang city which dispersed with nursery stock, sward and scrap leather, shared haplotype H22. The population from Nanyan village of Xinluo district, Longyan city, bore haplotype H36. Mitochondrial data reveals that the invasion history of S. invicta in Fujian Province is complex, including multiple invasions probably from other provinces within China. Security measures to prevent S. invicta spreading within China are as important as from overseas.

Eradication of Solenopsis invicta by pyriproxyfen at the Shihmen Reservoir in northern Taiwan

The aim of this study was to investigate the possibility of eradicating the red imported fire ant, Solenopsis invicta Buren, in the hot, humid and rainy conditions of northern Taiwan. Thirteen hectares of the Shihmen Reservoir have been infected with these ants, with a total of 1 578 mounds. Pyriproxyfen was applied at a rate of 2 kg/hectare each season, for a total of four seasons. Surveys using visual examination, bait traps, as well as the population index method showed that the brood, the reproductive ants, and the worker ants within the nests were all significantly reduced 1 month after the first application of pyriproxyfen. Four months after the initial application there were no more brood or reproductive ants. After 8 months there were no longer any active mounds left, and 12 months later there were no more worker ants. After monitoring for 1 more year, it was ascertained that the red imported fire ants were eradicated. The percentages of decrease after 2, 4 and 6 months of treatment were 57.4%, 80.5%, and 98.2%, respectively.

How do groups of red imported fire ants （Hymenoptera： Formicidae） feed on a droplet of sugar water？

Many previous studies have focused on the foraging behaviors and strategies of the red imported fire ants, Solenopsis invicta Buren on solid food or granular bait; little attention has been paid to how liquid sugar is fed upon. In the present study, behavioral responses ofS. invicta to 25% sucrose water droplets were observed. Five foraging patterns were identified in S. invicta colonies under laboratory conditions： （i） no feeding, no sucrose water feeding was observed; （ii） surround feeding, ants surrounded and fed along the edge of the sucrose droplet; （iii） stacked feeding, ants stacked and fed along the edge of the sucrose droplet; （iv） droplet-break feeding, ants broke the liquid droplet and sucked sucrose water that spread on surface of the substance or soil particles previously transported by ants; and （v） cover feeding, whole surface of the sucrose droplet was covered by layers of feeding ants. This is the first time cover feeding in S. invicta has been reported, which obviously requires more ants compared to the other patterns. In addition, individual ants were tracked in videos under laboratory conditions, and behavioral repertoires that led to stacking, covering and droplet-breaking were identified and described. The field investigation showed that surround feeding was most frequently performed by S. invicta foragers; however, cover feeding was not observed under field conditions during this study. Both laboratory and field studies showed colony-level variations in sugar-water feeding.

Advancement on techniques for the separation and maintenance of the red imported fire ant colonies

Advancement has recently been made on the techniques for separating and maintaining colonies of red imported fire ants, Solenopsis invicta Buren. A new brood rescue method significantly improved the efficiency in separating colony from mound soil. Furthermore, a new method was developed to separate brood from the colony using fire ant repellants. Finally, a cost-effective method was developed to coat containers with diluted Fluon （AGC Chemicals America, Inc, Moorestown, NJ, USA）, an aqueous polytetrafluoroethylene, to prevent housed ants from escaping a container. Usually the original Fluon solution is directly applied to the wall of the containers. Reduced concentrations of Fhion were found to be equally effective in preventing ant escape. The use of diluted Fluon solutions to coat the containers was recommended because of environmental and cost-saving benefits. Application of these new techniques can significantly reduce labor, cost and environmental contamination. This review paper collates all the new techniques in one reference which readers can use as a manual.

Red imported fire ants(Hymenoptera:Formicidae)cover inaccessible surfaces with particles to facilitate food search and transportation

Eusocial insects have evolved diverse particle-use behaviors.A previous study reported that red imported fire ants,Solenopsis invicta Buren,deposited soil particles on substances treated with essential balm,a fire ant repellent.We hypothesized that S.invicta modifies inaccessible surfaces by covering them with soil particles to facilitate food search and transportation.Here,laboratory experiments were conducted to study the particle-covering behavior of.S.invicta in response to viscose surfaces or surfaces treated with essential balm or liquid paraffin in the presence of real food(sausage)or non-food objects(acrylic plates).S.invicta workers deposited significantly more soil particles on these three types of treated surfaces than on untreated surfaces.In addition,significantly more particles were relocated on viscose and parafTin-smeared surfaces in the presence of food than in the presence of non-food objects.The particle-covering behavior on viscose surfaces was also observed in the field.Interestingly,when no soil particles were available,ants searched and transported food on viscose surfaces only if the surfaces were artificially covered with sufficient quantities of soil particles but could not do so on viscose surfaces without soil particles or with insutTicient quantities of soil particles.In addition,ants actively relocated particles to cover viscose surfaces if the transportation distance was within 200 mm,whereas significantly fewer particles were relocated at longer transportation distances(400 mm).Our study provides a novel example of particle use by fire ants during foraging.