红火蚁的社会型及其相关基因Gp-9的研究综述

红火蚁Solenopsis invicta Buren的蚁巢具有2种基本的社会组织形态:单后型和多后型。蚁巢中蚁后的数量是由工蚁和蚁后的基因型共同决定的。红火蚁的Gp-9基因编码一种气味结合蛋白并控制这种社会多态性的表达。Gp-9基因的发现首次证明单个基因在昆虫复杂的社会行为中起关键的作用。从红火蚁的社会型特征、Gp-9基因与不同社会型的关系以及Gp-9基因的相关研究对该领域的研究进展进行综述。     

Prevalence and impact of the microsporidium Thelohania solenopsae (Microsporidia) on wild populations of red imported fire ants, Solenopsis invicta, in Louisiana

We surveyed 165 sites to determine the ecological factors that might influence the distribution and prevalence of Thelohania solenopsae, and its effect on the demography of the red imported fire ant (Solenopsis invicta) in Louisiana. The microsporidium was found in 9.9% of colonies and at 16% of sites. Its distribution was clumped within the state with the majority of infected colonies and sites occurring in two infection patches. The proportion of polygyne colonies was a strong (positive) predictor of the proportion of infected colonies at a site. Infected monogyne colonies, however, still accounted for nearly 20% of infected colonies, a much higher proportion than anticipated. Several other factors, including the numbers of colonies at a site, precipitation, proximity to commercial waterways and ports, and type of habitat were also retained in the multiple logistic regression model describing T. solenopsae prevalence. The microsporidium appears to adversely affect the occurrence of brood, and possibly the size of S. invicta colonies and the mass of workers. It, however, was not included in the multiple regression model of the number of colonies or the density of ants at a site. Although our findings do not imply causation, they have identified several variables that might influence the epizootiology of T. solenopsae. Future work should concentrate on experimentally manipulating these variables to confirm these relationships.     

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."     

Enzyme polymorphisms in the fire ant,Solenopsis invicta (hymenoptera: formicidae)

A survey of allozyme variability in the fire ant, Solenopsis invicta Buren, was conducted using samples collected throughout the species' range in North America. A substantial amount of variability was found, although heterozygosity estimates were considerably less than estimates for diploid non-hymenopterous species. The presence of this variability raises the possibility of multiple introductions of this ant to North America. Although based on a limited sample, our data indicate no differences in variability between individuals from monogynous and polygynous populations or between individuals from the Mobile, Alabama area (presumed point of introduction) and outside the area. Individuals from polygynous colonies shared all detected alleles with individuals from monogynous colonies indicating the lack of long-term reproductive isolation between the two types of populations.     

Light and electron microscope study of Thelohania solenopsae n. sp. (Microsporida: Protozoa) in the red imported fire ant,Solenopsis invicta

A new species of Microsporida, Thelohania solenopsae, is described from the red imported fire ant, Solenopsis invicta. The Thelohania infections are localized in the fat body of workers. Meronts causing infections of progeny are found in the ovaries of queens. Spores occur only in adult ants and only vegetative stages are present in larvae and pupae. Both uninucleate octospores (eight spores within a pansporoblast membrane) and binucleate free spores (spores developing in isolation) are formed.     

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.     

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.     

Characterization of vitellogenin in the red imported fire ant, Solenopsis invicta (Hymenoptera: Apocrita: Formicidae)

Vitellin (VN) and vitellogenin (VG) profiles were analyzed in monogyne and polygyne colonies of the red imported fire ant, Solenopsis invicta. Non-denaturing and SDS-polyacrylamide gel electrophoresis (PAGE) analyses indicated that the native VN was likely 350 kDa and comprised of two subunits in the molecular size range of 170-185 kDa. SDS-PAGE of hemolymph showed that the relative mobilities and subunit patterns of VG and VN were similar. VG was present in the hemolymph of reproductive queens; alate, virgin queens; and workers, but not in males. Anti-VN, prepared from polygyne egg homogenates, reacted with egg homogenates and with hemolymph VG from reproductive, monogyne and polygyne queens and alate, virgin polygyne queens. Analysis of circulating VG and ovarian development in alate, virgin queens showed that low levels of VG appeared by five days following adult eclosion, but egg development was not observed until seven weeks. VG was evident in newly inseminated queens, and increased steadily for the first three weeks following dealation. VG levels declined slightly near eclosion of the first workers (= nanitics) and dropped sharply after nanitic emergence at five weeks following dealation. Oocyte maturation peaked at days 15-25 following dealation, but otherwise remained low but steady. These studies provide the basis for future investigations into endocrine regulations of vitellogenesis in S. invicta queens.     

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.     

Transmission of Vairimorpha invictae (Microsporidia: Burenellidae) infections between red imported fire ant (Hymenoptera: Formicidae) colonies

Red imported fire ant, Solenopsis invicta, colonies were successfully infected with the microsporidium Vairimorpha invictae by introducing live larvae, pupae, or dead adults from V. invictae-infected field colonies collected in Argentina. Introductions with 4th instar larvae or non-melanized pupae obtained from infected field colonies, resulted in infection of 40% of the inoculated colonies. Introductions of 4th instars or melanized pupae produced from colonies that were initially infected in the laboratory, resulted in infections of 83% of the colonies, thus perpetuating the infection in other colonies. Infection was detected in 2 of 6 colonies after introducing adult worker caste ants that had died with V. invictae. The average number of adults and the volume of immature ants per colony were significantly lower in the infected than in the control colonies. Infected colonies had 86% fewer adults per colony and 82% less immature ants than the controls. A portion of the 16S rRNA gene of the V. invictae identified from these studies was amplified, cloned, and sequenced; the 1251 nucleotide amplicon was 100% identical to the 16S rRNA gene sequence recorded previously in the GenBank database, thus verifying the species as V. invictae. This is the first report of the artificial transmission of this pathogen to uninfected ant colonies, and demonstration of its ability to hinder growth in individual colonies.     

EAG and behavioral responses of workers of the red imported fire ant,Solenopsis invicta Buren (Hymenoptera: Formicidae) to its trail pheromones

[目的]测定红火蚊Solenopsis invicta Buren工蚊对其跟踪信息素的触角电位(EAG)及行为反应.[方法]解剖红火蚁工蚁的杜氏腺,用正己烷溶剂提取其分泌的跟踪信息素进行气相色谱-质谱(GC-MS)分析,并测定了红火蚁工蚁对杜氏腺提取物、工蚁提取物和合成的法尼烯混合物的EAG和招募行为反应.[结果]通过与合成的法尼烯混合物的气相色谱(GC)保留时间和质谱图比对,发现杜氏腺提取物的主要成分并不是Z,E-α-法尼烯.EAG测定结果表明,红火蚁工蚁对杜氏腺提取物、工蚁提取物及100 μg的法尼烯混合物均有较强的EAG反应,其次为10μg和1 μg的法尼烯混合物.在招募行为测定中,杜氏腺提取物和工蚁提取物招募作用明显,而10,1,0.1和0.01 μg法尼烯混合物的作用均不显著.[结论]Z,E-α-法尼烯不是红火蚁跟踪信息素的主要成分;红火蚁工蚁对杜氏腺提取物、工蚁提取物有较强的EAG反应和明显的招募行为反应.