Chemical tools to distinguish the fire ant species Solenopsis invicta and S. saevissima (Formicidae: Myrmicinae) in Southeast Brazil

Morphologically similar fire ants Solenopsis invicta and Solenopsis saevissima are broadly sympatric in southeastern Brazil. Chemistry from venom (2,6-dialkyl piperidine alkaloids) and cuticular hydrocarbons have been reported as potentially important tools for differentiating Solenopsis species. We have analysed two chemical classes in widely separated populations of S. invicta and S. saevissima and find that both piperidine alkaloids and cuticular hydrocarbons separate the two species. Piperidine alkaloids clustered S. invicta but not S. saevissima. Cuticular hydrocarbons strongly clustered both S. invicta and S. saevissima. One population morphologically identified as S. invicta presented piperidine alkaloids and cuticular hydrocarbons markedly different from either species. The distinctive piperidine alkaloid differences among populations of S. saevissima and the marked difference in piperidine alkaloid and hydrocarbon profiles of the anomalous population of S. invicta suggest undescribed species fire ant in southeastern Brazil.     

Indirect effects of phorid fly parasitoids on the mechanisms of interspecific competition among ants

Indirect effects, which occur when the impact of one species upon another requires the existence of an intermediary species, are apparently very common and may be of greater magnitude than direct effects. Behaviorally mediated indirect effects occur when one species affects the behavior of a second, which in turn affects how that species interacts with a third. I studied behaviorally mediated indirect effects on the mechanisms of competition in two congeneric fire ant species in the presence and absence of parasitoid phorid flies, which parasitized only one ant species. In observational and experimental field studies, the presence of native Texas phorid flies in the genus Pseudacteon decreased food retrieval by their host, Solenopsis geminata (F.), by as much as 50%. In the presence of phorid flies, many S. geminata workers assumed a stationary, curled defensive posture and did not forage. Although the phorid parasitoids had a relatively large effect on exploitative competition, there was no measurable effect on interference competition. Fierce interspecific aggression was observed between S. geminata and S. invicta Buren, and the presence of phorids had no effect on the outcome of these contests. The indirect effects of Pseudacteon parasitoids on Solenopsis fire ant resource retrieval appear to be larger than the direct effect of mortality. Some aspects of the foraging behavior of these Solenopsis species may be, in part, evolutionary adaptations to phorid parasitoid pressure. Because of the relatively large indirect effects, South American Pseudacteon phorids may be promising biocontrol agents of imported fire ants, S. invicta, in the USA. In a laboratory study, a single South American Pseudacteon female was able to significantly decrease food retrieval rates of a North American population of the imported fire ant, S. invicta. Received: 11 May 1998 / Accepted: 18 April 1999     

The Guianese population of the fire ant Solenopsis saevissima is unicolonial

In this study, conducted in French Guiana, a part of the native range of the fire ant Solenopsis saevissima, we compared the cuticular hydrocarbon profiles of media workers with previous results based on intraspecific aggressiveness tests. We noted a strong congruence between the two studies permitting us to delimit 2 supercolonies extending over large distances (up to 54 km), a phenomenon known as unicoloniality. Solenopsis geminata workers, taken as an out‐group for cluster analyses, have a very different cuticular hydrocarbon profile. Because S. saevissima has been reported outside its native range, our conclusion is that this species has the potential to become invasive because unicoloniality (i.e., the main attribute for ants to become invasive) was shown at least for the Guianese population.     

DNA barcoding of the fire ant genus Solenopsis Westwood (Hymenoptera: Formicidae) from the Riyadh region,the Kingdom of Saudi Arabia

The ant genus Solenopsis Westwood, 1840 is the largest in Myrmicinae subfamily having almost 200 described species worldwide. They are commonly distributed in the tropics and temperate areas of the world. Some invasive Solenopsis species are very dreadful. We have already reported a fire ant species, Solenopsis saudiensis Sharaf & Aldawood, 2011, identified using traditional morphometric approaches of species identification. Present study was carried out to develop DNA Barcoding to identify Solenopsis saudiensis and to elucidate genetic structure of the various S. saudiensis populations across their distribution range in Riyadh, Saudi Arabia. The comparison of DNA barcodes showed no genetic diversity among six populations and a queen from S. saudiensis analyzed from the Riyadh region. This genetic resemblance probably reflects their adaptation toward a specific habitat, thus constituting a single and strong gene pool. Our comprehensive field survey did not provide any evidence of Solenopsis species except S. saudiensis in the Riyadh region. Solenopsis saudiensis populations were only found around date palm trees indicating their strong association with date palm groves. Moreover, S. saudiensis has 83–86% sequence identity to other Solenopsis spp. from other parts of the world. Interestingly, the highest sequence identity of (86%) was with that of Solenopsis molesta Say, 1836, the thief ant, from the USA. This study provides a working laboratory procedure and a reference library for the identification of Solenopsis saudiensis.     

Bacterial Diversity in <Emphasis Type="Italic">Solenopsis invicta</Emphasis> and <Emphasis Type="Italic">Solenopsis geminata</Emphasis> Ant Colonies Characterized by 16S amplicon 454 Pyrosequencing

Social insects harbor diverse assemblages of bacterial microbes, which may play a crucial role in the success or failure of biological invasions. The invasive fire ant Solenopsis invicta (Formicidae, Hymenoptera) is a model system for understanding the dynamics of invasive social insects and their biological control. However, little is known about microbes as biotic factors influencing the success or failure of ant invasions. This pilot study is the first attempt to characterize and compare microbial communities associated with the introduced S. invicta and the native Solenopsis geminata in the USA. Using 16S amplicon 454 pyrosequencing, bacterial communities of workers, brood, and soil from nest walls were compared between neighboring S. invicta and S. geminata colonies at Brackenridge Field Laboratory, Austin, Texas, with the aim of identifying potential pathogenic, commensal, or mutualistic microbial associates. Two samples of S. geminata workers showed high counts of Spiroplasma bacteria, a known pathogen or mutualist of other insects. A subsequent analysis using PCR and sequencing confirmed the presence of Spiroplasma in additional colonies of both Solenopsis species. Wolbachia was found in one alate sample of S. geminata, while one brood sample of S. invicta had a high count of Lactococcus. As expected, ant samples from both species showed much lower microbial diversity than the surrounding soil. Both ant species had similar overall bacterial diversities, although little overlap in specific microbes. To properly characterize a single bacterial community associated with a Solenopsis ant sample, rarefaction analyses indicate that it is necessary to obtain 5,000–10,000 sequences. Overall, 16S amplicon 454 pyrosequencing appears to be a cost-effective approach to screen whole microbial diversity associated with invasive ant species.     

Post-Release Host-Specificity Testing of Pseudacteon tricuspis, a Phorid Parasitoid of Solenopsis Invicta Fire Ants

Inherent in any biological control program is the risk of nontarget effects. Pseudacteon tricuspisBorgmeier, a parasitoid phorid fly, has been introduced to the United States from South America as a potential biocontrol agent of the red imported fire ant, Solenopsis invictaBuren. We conducted tests of host specificity on introduced populations of P. tricuspis, which are attracted to alarm pheromones released by their hosts during events such as mound disturbances and interspecific interactions. We monitored disturbed mounds of S. invicta and its close congener, S. geminata(F.), during the expansion of P. tricuspis across north Florida and after populations had been established for ~3 years. We also tested host acceptance in established populations of P. tricuspis by offering trays containing S. invicta, S. geminata, and 14 additional ant species representing 12 different non-Solenopsis genera. Although P. tricuspiswas commonly observed to hover over and attempt to oviposit on S. invicta, we never observed any parasitization attempts on any other ant species. As predicted by laboratory tests, released populations of P. tricuspis appear to be highly host specific and pose no obvious threat to nontarget species.     

New Family,Genus, and Species of Microsporida (Protozoa: Microsporida) from the Tropical Fire Ant,Solenopsis geminata (Fabricius) (Insecta: Formicidae)*

SYNOPSIS. A new species of Microsporida, Burenella dimorpha sp. n., representing a new family, Burenellidae fam. n. and genus, is described on the basis of light- and electron-microscope observations. The family is characterized by 2 sequences of sporogony, each sequence having morphologically different sporonts and spores. The parasite infects the tropical fire ant, Solenopsis geminata (Fabricius), producing distinct pathologic manifestations (clearing of the cuticle and eye malformation) and death in the pupal stage of development. Transmission of the infection per os to healthy S. geminata, to the Southern fire ant, Solenopsis xyloni McCook, and to the red and black imported fire ants, Solenopsis invicta Buren and Solenopsis richteri Forel, is reported.     

Molecular diversity of the microsporidium Kneallhazia solenopsae reveals an expanded host range among fire ants in North America

Kneallhazia solenopsae is a pathogenic microsporidium that infects the fire ants Solenopsis invicta and Solenopsis richteri in South America and the USA. In this study, we analyzed the prevalence and molecular diversity of K. solenopsae in fire ants from North and South America. We report the first empirical evidence of K. solenopsae infections in the tropical fire ant, Solenopsis geminata, and S. geminata × Solenopsis xyloni hybrids, revealing an expanded host range for this microsporidium. We also analyzed the molecular diversity at the 16S ribosomal RNA gene in K. solenopsae from the ant hosts S.invicta, S. richteri, S. geminata and S. geminata × S. xyloni hybrids from North America, Argentina and Brazil. We found 22 16S haplotypes. One of these haplotypes (WD_1) appears to be widely distributed, and is found in S. invicta from the USA and S. geminata from southern Mexico. Phylogenetic analyses of 16S sequences revealed that K. solenopsae haplotypes fall into one of two major clades that are differentiated by 2-3%. In some cases, multiple K. solenopsae haplotypes per colony were found, suggesting either an incomplete homogenization among gene copies within the 16S gene cluster or multiple K. solenopsae variants simultaneously infecting host colonies.     

The effects of hydramethylnon on the tropical fire ant, <Emphasis Type="Italic">Solenopsis geminata</Emphasis> (Hymenoptera: Formicidae), and non-target arthropods on Spit Island,Midway Atoll,Hawaii

Invasive ants can cause major disruptions in native ecosystems. Ant eradication methods without significant non-target effects are needed to stop incipient invasions and to aid in ecosystem restoration. Successful ant eradications are rare and there is very little understanding of the effects of ant eradication methods, such as the use of formicides, on non-target species. Here we attempted to control and possibly eradicate the invasive tropical fire ant, Solenopsis geminata, from a small islet using the formicide Maxforce^® (active ingredient: hydramethylnon), and to quantify the non-target effects on an almost exclusively alien ground-dwelling arthropod community. S. geminata abundance was reduced and the species was not detected on bait cards for 12 months post-treatment. The abundance of another non-target invasive ant that was primarily detected in pitfall traps, Tetramoruim bicarinatum, declined in pitfall traps following treatment, but seemed to be excluded from bait cards by S. geminata. Total ant abundance did not return to original levels until more than 12 months post-treatment. Populations of alien cockroaches (Order Blattaria) and crickets (Orthoptera: Gryllidae) were negatively affected by the treatment. We conclude that Maxforce^® can be used to control small infestations of S. geminata and T. bicarinatum effectively; however we recommend it be used cautiously due to the potential ecological cost to non-target species. Use in areas where infestations are small and isolated will maximize the likelihood of success while minimizing non-target effects.     

Composition of harvested seeds and seed selection by the invasive tropical fire ant, <Emphasis Type="Italic">Solenopsis geminata</Emphasis> (Hymenoptera: Formicidae) in Taiwan

Solenopsis geminata (F.) is an invasive ant that is widely distributed in weedy areas and agricultural fields in Taiwan. Previous studies have found that S. geminata harvests the seeds of numerous plants. In the present study, we further investigated the composition of harvested seeds in ant nests and seed selection by workers. The seed caches in S. geminata nests sampled in eight areas in Taiwan suggest that the seeds harvested by workers were diverse and belonged to 52 plant species in 17 plant families. Twenty-three species (44%) belong to the family Gramineae, and most of the seeds weighed from 0.02 to 2.29 mg, which might suggest that these are the main seeds harvested by S. geminata from their habitat. Ten common species with similar seed weights were used to compare the seed preferences of workers from two experimental sites. The results suggest that the seed preference was different between the two experimental sites. The seeds of Casuarina equisetifolia showed the most obvious difference in seed removal speed, which might suggest that S. geminata potentially prefers the encountered seed species in the habitat. The various plant species in the ant nests and seed preference suggest that fire ants easily accept newly encountered plant species. As more than half of the plant species (52%) and the total seed number (63%) belonged to exotic species, the role of S. geminata might be negative because it tends to harvest exotic seeds and has a high opportunity to improve the establishment of exotic seedlings.     

Manipulating tropical fire ants to reduce the coffee berry borer

1. The coffee berry borer Hypothenemus hampei (Coleoptera, Curculionidae) (Ferrari) is the most important pest of coffee production worldwide. 2. The hypothesis that the tropical fire ant, Solenopsis geminata Westwood, indirectly protects the coffee berry borer by suppressing other ant species that are the coffee berry borer's primary predators was tested. 3. It was found that removing S. geminata from coffee plots significantly increased the disappearance of adult coffee berry borer beetles from coffee berries compared with control plots. An average of 6% of beetles disappeared from plots with S. geminata whereas 23% of beetles disappeared from plots from which S. geminata was removed. This pattern was observed on two shade coffee farms with marked differences in ant species composition, one in the rainforest in central Costa Rica and one in the cloudforest in northwest Costa Rica. 4. If the results of this small‐scale study can be replicated on the farm level, then S. geminata suppression may represent a new management technique for the coffee berry borer throughout Central and South America.     

Traits allowing some ant species to nest syntopically with the fire ant Solenopsis saevissima in its native range

Supercolonies of the red fire ant Solenopsis saevissima (Smith) develop in disturbed environments and likely alter the ant community in the native range of the species. For example, in French Guiana only 8 ant species were repeatedly noted as nesting in close vicinity to its mounds. Here, we verified if a shared set of biological, ecological, and behavioral traits might explain how these 8 species are able to nest in the presence of S. saevissima. We did not find this to be the case. We did find, however, that all of them are able to live in disturbed habitats. It is likely that over the course of evolution each of these species acquired the capacity to live syntopically with S. saevissima through its own set of traits, where colony size (4 species develop large colonies), cuticular compounds which do not trigger aggressiveness (6 species) and submissive behaviors (4 species) complement each other.     

Ecological interactions of Pseudacteon parasitoids and Solenopsis ant hosts: environmental correlates of activity and effects on competitive hierarchies

1. Solenopsis (Hymenoptera: Formicidae) fire ants are host to Pseudacteon (Diptera: Phoridae) parasitoids. The activity of S. geminata (F.) hosts and relative abundance of Pseudacteon phorids, along with five environmental variables, were measured at weekly intervals over an 8‐month period at two sites. 2. Pseudacteon relative abundances often varied greatly from week to week, and were only weakly positively correlated with S. geminata activity. 3. A quadratic function of soil temperature was the single best predictor of ant activity at both sites, explaining 32 and 73% of the variation in ant activity. A linear function of soil moisture was the single best predictor of phorid relative abundance at one site (r² = 0.23) whereas no measured variables were significant predictors of phorid relative abundance at the other site. 4. Interspecific interactions at 600 baits were monitored at a third site to document dominance hierarchies and determine whether the presence of Pseudacteon phorids mediated interspecific interactions in their host, S. geminata. 5. Solenopsis geminata was near the top of dominance hierarchies, which did not diverge greatly from a linear pattern. Three species (S. geminata, S. invicta Buren, and Crematogaster laeviuscula Mayr) won the majority of their interspecific interactions and appear to be co‐dominants at this microhabitat‐rich site. 6. Overall, the presence of phorids had no significant effect on the outcome of interspecific contests involving S. geminata and all other ant species grouped together. Phorids may have contributed to some of the S. geminata losses against other co‐dominant species.     

Ants of the Genus Solenopsis Westwood 1840 (Hymenoptera: Formicidae) in the Arabian Peninsula with Description of a New Species,Solenopsis elhawagryi

Ants of the genus Solenopsis Westwood in the Arabian Peninsula are revised. Six species are treated: Solenopsis elhawagryi Sharaf & Aldawood sp. n., S. geminata (Fabricius, 1804), S. omana Collingwood & Agosti, 1996, S. saudiensis Sharaf & Aldawood, 2011, S. sumara Collingwood & Agosti, 1996, and S. zingibara Collingwood & Agosti, 1996. Solenopsis elhawagryi is described from Beljorashi Governorate, Al Baha Province, Saudi Arabia, based on worker castes and the queen with notes on this species biology and ecology. Solenopsis sumara workers are redescribed and illustrated for the first time and a lectotype is designated. An identification key to the Arabian and Egyptian species is provided with scanning electron micrographs to facilitate species recognition.     

Organic linings in nests of the fire ants Solenopsis electra Forel and Solenopsis nr. macdonaghi Santschi from Argentina

Although fire ants have been extensively studied, not much has been published about the structure and building material of their nests and even less on the lining of chamber walls. Nests built in unconsolidated sandy soils of Solenopsis electra and Solenopsis nr. macdonaghi, studied in La Pampa and Chubut (Argentina), respectively, show organic linings, which are reported herein for the first time. It is hypothesized that these organic linings may be of fecal origin, since there is no organic rich horizon in those soils. Apart from its significance as regards ant architecture and nest function, the presence of organic linings in ant nests is important for interpreting fossil nests, which have been often assigned to termites based on the presence of organic linings.     

Booms,busts and population collapses in invasive ants

The abundance of many invasive species can vary substantially over time, with dramatic population declines and local extinctions frequently observed in a wide range of taxa. We highlight population crashes of invasive ants, which are some of the most widespread and damaging invasive animals. Population collapse or substantial declines have been observed in nearly all of the major invasive ant species including the yellow crazy ant (Anoplolepis gracilipes), Argentine ants (Linepithema humile), big-headed or coastal brown ant (Pheidole megacephala), the tropical fire ant (Solenopsis geminata), red imported fire ants (Solenopsis invicta), and the little fire ant or electric ant (Wasmannia auropunctata). These declines frequently attract little attention, especially compared with their initial invasion phase. Suggested mechanisms for population collapse include pathogens or parasites, changes in the food availability, or even long-term effects of the reproductive biology of invasive ants. A critical component of the collapses may be a reduction in the densities of the invasive ant species, which are often competitively weak in low abundance. We propose that mechanisms causing a reduction in invasive ant abundance may initiate a local extinction vortex. Declines in abundance likely reduce the invasive ant’s competitive ability, resource acquisition and defense capability. These reductions could further reduce the abundance of an invasive ant species, and so on. Management of invasive ants through the use of pesticides is expensive, potentially ecologically harmful, and can be ineffective. We argue that pesticide use may even have the potential to forestall natural population declines and collapses. We propose that in order to better manage these invasive ants, we need to understand and capitalize on features of their population dynamics that promote population collapse.     

Reproduction by virgin queen fire ants in queenless colonies: Comparative study of three taxa (Solenopsis richteri,hybridS. invicta/richteri,S. geminata) (Hymenoptera: Formicidae)

Summary In the fire ant,Solenopsis invicta, some winged virgin queens are known to shed their wings (dealate) upon removal of the mated mother queen. These virgin queens then develop their ovaries and begin to lay eggs, thereby foregoing the option of leaving on mating flights and attempting to found their own colonies. Such a response of virgin queens to queenlessness has not been reported for other ants. In order to determine if virgin queens of some other fire ants (subgenusSolenopsis) would respond in the same way, experiments were conducted onS. richteri, hybridS. invicta/richteri andS. geminata, a member of a species complex different from that of the other taxa. Just as inS. invicta, virgin queens ofS. richteri and the hybrid dealated and began to lay eggs within days of the removal of the queen. In addition, workers executed many of the reproductively active virgin queens, a phenomenon also found inS. invicta. In contrast, virgin queens ofS. geminata did not dealate or quickly begin to lay eggs upon separation from the queen. Reasons for the variability in the response of virgin queens of the different species may be 1) higher probability of reproductive success for unmated dealated queens compared to normal claustral founding inS. invicta andS. richteri linked to relatively frequent loss of the mother queen; or 2) phylogenetic constraint.     

Fire ants: What do rural and urban areas show us about occurrence, diversity,and ancestral state reconstruction?

In South America, Solenopsis saevissima and S. invicta are the most common fire ants. Nests are founded in areas under anthropic interference like urban or rural areas, but S. invicta is found preferentially in those with the greatest anthropic interference. However, we do not know the rates at which they exist in anthropized areas next to high density of native vegetation. Areas with 60 to 90% of native Atlantic Forest were selected to verify the occurrence of both species in rural and urban areas. We investigated the molecular diversity and applied the reconstruction of the ancestral state analysis for each species. A total of 186 nests were analyzed and we found that the two species had the same proportion in the urban area. However, S. saevissima had a higher rate of prevalence in the rural area, in addition to having a greater number of haplotypes and ancestry associated with this type of habitat for the region. S. invicta had the same number of haplotypes in both rural and urban regions, and less haplotypic diversity. We conclude that S. saevissima is a species typically associated with rural areas and S. invicta, although present, is not dominant in urban areas. Keywords: Biodiversity, haplotype diversity, DNA barcoding, mtDNA     

COMPARATIVE BIOCHEMICAL GENETICS OF THREE FIRE ANT SPECIES IN NORTH AMERICA,WITH SPECIAL REFERENCE TO THE TWO SOCIAL FORMS OF SOLENOPSIS INVICTA (HYMENOPTERA: FORMICIDAE)

An electrophoretic study of the genetics of three fire ant species in North America was undertaken with the primary objective of further clarifying the genetic relationship between two social forms of Solenopsis invicta. Such social forms are common in many groups of ants and may, in some cases, represent significant intermediate stages in the speciation process. The monogyne and polygyne forms of S. invicta, while differing in a number of important biological traits, are genetically indistinguishable, in contrast to the substantial genetic differentiation observed between S. invicta and a second, closely related, introduced species, S. richteri. The native fire ant, S. geminata, is genetically the most distinct of the three species studied, in accord with its taxonomic placement in a different species complex. Hypotheses concerning the derivation of the polygyne form of S. invicta from the monogyne form which invoke their long-term reproductive isolation in South America and separate introductions to North America appear unfounded. Although S. invicta and S. richteri are known to hybridize in North America, our study provided no evidence of gene introgression between S. invicta and the native species, S. geminata, in areas where our samples were collected. Analyses of population structure in S. invicta failed to reveal significant differentiation of populations or local inbreeding. Levels of genetic diversity in the three species studied, although not significantly different, were in the order predicted from knowledge of the population biology and recent history of the taxa, with S. richteri exhibiting the least diversity, S. geminata the greatest, and S. invicta having an intermediate level.     

The ecological role of ants in two Mexican agroecosystems

Summary The development of the ant communities and their foraging dynamics were studied in two annual agroecosystems of the Mexican tropical lowlands: a forest milpa of corn, beans, and squash made by cutting and buring 40-year-old forest, and a field milpa of corn, beans, and squash made by plowing 1-year-old second growth. The ant community was sampled using tuna fish baits 26, 52, 110 and 353 days after planting. Although immediately after planting the same number of ant species occurred in each milpa type, thereafter the ant faunas diverged. The field milpa became completely dominated by the native fire ant, Solenopsis geminata, while the number of ant species in the forest milpa gradually increased over time, reaching eight species 110 days after planting and 14 species by 353 days. Initially S. geminata dominated the ant fauna in the forest milpa (occurring on 90% of the baits), but by 353 days planting it was found on only 26% of the occupied baits. Ant foraging efficiency, as measured by proportion of tuna baits occupied and the removal rates of dead Drosophila fly baits, was much higher (by a factor of 2 to 3) in the field than the forest milpa. This was caused by the extremely high density of S. geminata colonies in the field milpa. The simple Solenopsis-dominated community of the field milpa may be much more effective in biological control than the more diverse community of the forest milpa. Although S. geminata has potential negative impacts in annual agroecosystems (it stings, eats corn seeds, and guards homopterams), its overall impact appears to be beneficial. As forested areas of the lowland wet tropics are increasingly cut and converted to annual agriculture, the primary ant inhabitant of these highly disturbed environments, S. geminata, will necessarily play a much more significant ecological role in agroecosystems.