Monomorium Pharaonis Research Articles

Multilocus genetic characterization of two ant vectors (Group II "Dirty 22" species) known to contaminate food and food products and spread foodborne pathogens.

The U.S. Food and Drug Administration utilizes the presence of filth and extraneous materials as one of the criteria for implementing regulatory actions and assessing adulteration of food products of public health importance. Twenty-two prevalent pest species (also known as the ''Dirty 22'' species) have been considered by this agency as possible vehicles for the spread of foodborne diseases, and the presence of these species is considered an indicator of unsanitary conditions in food processing and storage facilities. In a previous study, we further categorized the Dirty 22 species into four groups: group I includes four cockroach species, group II includes two ant species, group III includes 12 fly species, and group IV includes four rodent species. Here, we describe the development of three nested PCR primer sets and multilocus genetic characterization by amplifying the small subunit rRNA, elongation factor 1-alpha, and wingless (WNT-1) genes of group II Dirty 22 ant species Monomorium pharaonis and Solenopsis molesta. These novel group II Dirty 22 species-specific nested PCR primer sets can be used when the specimens cannot be identified using conventional microscopic methods. These newly developed assays will provide correct identification of group II Dirty 22 ant species, and the information can be used in the control of foodborne pathogens.

Better the nest site you know: decision-making during nest migrations by the Pharaoh’s ant

Animals frequently have to decide between alternative resources and in social insects these individual choices produce a colony-level decision. The choice of nest site is a particularly critical decision for a social insect colony to make, but the decision making process has still only been studied in a few species. In this study, we investigated nest selection by the Pharaoh’s ant, Monomorium pharaonis, a species renowned for its propensity to migrate and its use of multi-component trail pheromones to organise decision-making in other contexts. When presented with the choice of familiar and novel nests of equal quality in a Y set-up, colonies preferentially migrated towards the familiar nest, suggesting a form of colony-level ‘memory’ of potential nest sites. However, if the novel nest was superior to the familiar nest, then colonies began migrating initially to the familiar nest, but then redirected their migration to the superior quality novel nest. This may be an effective method of reducing colony exposure while searching for an optimum nest site. Branches that had previously led to a selected nest were attractive to ants in subsequent migrations, suggesting that trail pheromones mediate the decision making process. The adaptive, pheromone-based organisation of nest-site selection by Pharaoh’s ants matches their ephemeral environment and is likely to contribute to their success as a 'tramp' species.

No benefit in diversity? The effect of genetic variation on survival and disease resistance in a polygynous social insect

1. Multiple mating by queens has been shown to enhance disease resistance in insect societies, because higher genetic diversity among nestmates improves collective immune defences or offers a certain level of herd immunity. However, it has remained ambiguous whether polygynous societies with large numbers of queens also benefit from increased genetic diversity. 2. We used one of the very few ant species that can be reared across generations, the pharaoh ant, Monomorium pharaonis Linnaeus, to create experimental colonies with two types of enhanced genetic diversity: (i) mixed workers from three divergent inbred lineages representing the ‘polygyny-equivalent' of multiple mating by queens (i.e. increased between-worker variation); and (ii) uniform workers whose overall heterozygosity was increased by two subsequent generations of crossing between the same divergent inbred lineages (i.e. increased within-worker variation). 3. We found significant differences in worker survival among the three inbred lineages, with exposure to conidiospores of the fungal pathogen Beauveria bassiana causing significant mortality to the workers independently of their diversity type. Increased diversity did not improve the resistance to Beauveria. 4. Enhanced heterozygosity colonies had worker survival rates similar to the most resistant inbred lineage, whereas colonies with mixed workers from the three inbred lineages had lower worker and larval survival. Workers did not show any infection-avoidance behaviour. 5. Average larval survival appeared unaffected by the presence of conidiospores. It benefitted from increased heterozygosity but was reduced in mixed colonies independent of infection. This suggests that negative, but cryptic social interactions in mixed colonies may affect overall survival. 6. The present results do not provide evidence for or against a link between increased genetic variation and increased disease resistance in pharaoh ants, but show that colonies differ considerably in general survival. Thus, increasing the genetic diversity of pharaoh ant colonies may not provide survival advantages in the face of pathogen exposure, and polygyny and polyandry may not be directly comparable mechanisms for creating adaptive resistance towards pathogens.

Development of a Bait System for the Pharaoh’s Ant, <i>Monomorium Pharaonis</i> L. (Hymenoptera: Formicidae)

The infestation of the Pharaoh’s ant, Monomorium pharaonis L. is widespread and, sometimes, very serious in homes, hospitals, restaurants, factories, etc. People are helpless because effective baited traps are not available locally, and little has been done locally to develop effective control strategies for these ants. The study aimed at developing an appropriate bait system from local materials for the control of the Pharaoh’s ant. Nine baits and three insecticides were evaluated in the laboratory and field situations. Groundnut cake, dry fish and granulated sugar were the most attractive baits. Rimon (a Benzoylphenyl urea), an insect growth regulator, was the most promising insecticide for incorporation into the bait system. It is, therefore, recommended that a bait system, containing groundnut cake, sugar and dry fish, mixed with 1% Rimon, be evaluated for Pharaoh’s ant control.

Ants (Hymenoptera: Formicidae) in five hospitals of Porto Alegre, Rio Grande do Sul State, Brazil

The presence of ants in hospitals is health risk for the hospital community, since presents a strong capability to carry pathogenic organisms throughout this environment. This study was carried out from May 2007 to April 2008, aiming the identification of ant species that infest the hospitals in Porto Alegre, Rio Grande do Sul State, Brazil. A total of 989 ants from 19 species were sampled: Acromyrmex niger (Fr. Smith, 1858), Brachymyrmex sp., Camponotus rufipes (Fabricius, 1775), Camponotus sericeiventris (Guerin-Meneville, 1838), Camponotus sp1, Camponotus sp2, Gnamptogenys sp., Hypoponera sp., Labidus coecus (Latreille, 1802), Monomorium pharaonis (Linnaeus, 1758), Pachycondyla sp., Paratrechina fulva (Mayr, 1862), Paratrechina longicornis Latreille, 1802, Pheidole sp1, Pheidole sp2, Pheidole sp3, Pheidole sp4, Pheidole sp5, and Tapinoma melanocephalum Fabricius, 1793. Among them, Brachymyrmex sp. was the most frequent one (47.0%) followed by Monomorium pharaonis (18.7%) and Labidus coecus (17.2%).

Queen–worker caste ratio depends on colony size in the pharaoh ant (Monomorium pharaonis)

The success of an ant colony depends on the simultaneous presence of reproducing queens and non-reproducing workers in a ratio that will maximize colony growth and reproduction. Despite its presumably crucial role, queen–worker caste ratios (the ratio of adult queens to workers) and the factors affecting this variable remain scarcely studied. Maintaining polygynous pharaoh ant (Monomorium pharaonis) colonies in the laboratory has provided us with the opportunity to experimentally manipulate colony size, one of the key factors that can be expected to affect colony level queen–worker caste ratios and body size of eclosing workers, gynes and males. We found that smaller colonies produced more new queens relative to workers, and that these queens and workers both tended to be larger. However, colony size had no effect on the size of males or on the sex ratio of the individuals reared. Furthermore, for the first time in a social insect, we confirmed the general life history prediction by Smith and Fretwell (Am Nat 108:499–506, 1974) that offspring number varies more than offspring size. Our findings document a high level of plasticity in energy allocation toward female castes and suggest that polygynous species with budding colonies may adaptively adjust caste ratios to ensure rapid growth.

Inter- and Intraspecific Aggression in the Invasive Longlegged Ant (Hymenoptera: Formicidae)

The longlegged ant, Anoplolepis gracilipes (Fr. Smith) (Hymenoptera: Formicidae), is a highly invasive species that can aggressively displace other ant species. We conducted laboratory assays to examine interspecies aggression of A. gracilipes versus 15 sympatric ant species found in the urban environment and disturbed habitat in Malaysia: Monomorium pharaonis (L.), Monomorium floricola (Jerdon), Monomorium orientale Mayr, Monomorium destructor (Jerdon), Pheidole parva Mayr, Crematogaster sp., Solenopsis geminata (F.), Tapinoma indicum (Forel), Tapinoma melanocephalum (F.), Technomyrmnex butteli Forel, Dolichoderus thoracicus (Smith), Paratrechina longicornis (Latrielle), Oecophylla smaragdina (F), Camponotus sp., and Tetraponera rufonigra (Jerdon). A. gracilipes showed aggressive behavior toward all opponent species, except the smallest M. orientale. Opponent species size (body size, head width, and mandible width) was significantly correlated with A. gracilipes aggression level and mortality rate. We also found a significant positive relationship between A. gracilipes aggression level and the mortality of the opponent species. The results suggest that invasive populations of A. gracilipes would have the greatest impact on larger ant species. In addition, we examined the intraspecific aggression of A. gracilipes. We found that A. gracilipes from different localities in Malaysia showed intraspecific aggression toward one another. This finding differs from the results of studies conducted in Christmas Island earlier. Differences in the genetic variability among populations may explain these differing results.

Decentralized communication, trail connectivity and emergent benefits of ant pheromone trail networks

Communication improves decision-making for group-living animals, especially during foraging, facilitating exploitation of resources. Here we model the trail-based foraging strategy of Pharaoh’s ants to understand the limits and constraints of a specific group foraging strategy. To minimise assumptions we used model parameters acquired through behavioural study. Pharaoh’s ants (Monomorium pharaonis) exploit the geometry of trail networks bifurcations to make U-turns, if they are walking the wrong way. However, 7% of foragers perform apparently incorrect U-turns. These seemingly maladaptive U-turns are performed by a consistent minority of specialist U-turners that make frequent U-turns on trails and lay trail pheromones much more frequently compared to the rest of the colony. Our study shows a key role for U-turning ants in maintaining the connectivity of pheromone trails. We produced an agent-based model of a heterogeneous ant community where 7% of agents were specialised frequent U-turners whilst the remaining 93% rarely U-turned. Simulations showed that heterogeneous colonies enjoyed significantly greater success at foraging for distant food resources compared to behaviourally homogeneous colonies. The presence of a cohort of specialised trail-layers maintains a well-connected network of trails which ensures that food discoveries are rapidly linked back to the nest. This decentralised information transfer might ensure that foragers can respond to dynamic changes in food distribution, thereby allowing more individuals in a group to benefit by successfully locating food finds.

Methyl 3-bromomethyl-3-butenoate as an isopentane building block for the stereoselective preparation of (S)-4-methyl-3,6-dihydro-2H-pyran-2-carbaldehyde and (+)-faranal

(S)-4-Methyl-3,6-dihydro-2H-pyran-2-carbaldehyde (3), the common intermediate in the syntheses of the C17–C27 subunit of laulimalide (4) and (+)-faranal (5), the trail pheromone of the pharaoh ant, Monomorium pharaonis, were obtained via transformation of methyl 3-bromomethyl-3-butenoate (1) into allylstannane 2 and subsequent allylation of (benzyloxy)acetaldehyde (6) in accordance with the Keck procedure as the key steps.

Low levels of nestmate discrimination despite high genetic differentiation in the invasive pharaoh ant

BackgroundAnts typically distinguish nestmates from non-nestmates based on the perception of colony-specific chemicals, particularly cuticular hydrocarbons present on the surface of the ants' exoskeleton. These recognition cues are believed to play an important role in the formation of vast so-called supercolonies that have been described for some invasive ant species, but general conclusions about the role of these cues are hampered by only few species being studied. Here we use data on cuticular hydrocarbons, aggression and microsatellite genetic markers to investigate the interdependence of chemical recognition cues, genetic distance and nestmate discrimination in the pharaoh ant (Monomorium pharaonis), a widespread pest species, and ask whether introduced populations of this species are genetically differentiated and exhibit intraspecific aggression.ResultsMicrosatellite analyses of a total of 35 colonies from four continents revealed extremely high levels of genetic differentiation between almost all colonies (FST = 0.751 ± 0.006 SE) and very low within-colony diversity. This implies that at least 34 and likely hundreds more independent lineages of this ant have spread worldwide. Aggression tests involving workers from 14 different colonies showed only low levels of aggression, even between colonies that were geographically and/or genetically very distant. Chemical analyses of groups of worker ants showed that all colonies had the same cuticular compounds, which varied only quantitatively among colonies. There was a positive correlation between geographical and genetic distance, but no other significant relationships were detected between aggression, chemical profile, genetic distance and geographical distance.ConclusionsThe pharaoh ant has a global invasion history of numerous independent introductions resulting in genetically highly differentiated colonies typically displaying surprisingly low levels of intraspecific aggression, a behaviour that may have evolved in the native range or by lineage selection in the introduced range.

Colony Budding and its Effects on Food Allocation in the Highly Polygynous Ant, Monomorium pharaonis

AbstractTo advance our understanding of the causes and the consequences of budding (colony multiplication by fragmentation of main nests), we investigated nest movement in the facultatively polydomous Pharaoh ant, Monomorium pharaonis. Demographic data revealed that Pharaoh ants are highly polygynous and have a relatively low worker to queen ratio of 12.86. Budding experiments demonstrated that the number of available bud nests has a significant effect on colony fragmentation and increasing the number of bud nests resulted in smaller colony fragments. The overall distribution among bud nests was uneven, even though there was no evidence that the different life stages and castes partitioned unevenly among the bud nests and the analysis of individual colonies revealed no evidence of an uneven split in any of the colonies. This demonstrates that Pharaoh ants have the ability to exert social control over colony size and caste proportions during budding, which may contribute to their success as an invasive ant. The intensity of nest disturbance had a significant effect on whether or not the ants migrated into bud nests. Major disturbance resulted in the ants abandoning the source nest and migrating to bud nests and minor disturbance did not stimulate the ants to abandon the source nest. The results of the successive budding experiment which allowed the ants the opportunity to bud into progressively smaller nest fragments demonstrate that Pharaoh ants maintain a preferred minimum group size of 469 ± 28 individuals. Food allocation experiments utilizing protein marking revealed that nest fragmentation in Pharaoh ants has no negative impact on intracolony food distribution. Overall, our results suggest that nest units in the Pharaoh ant behave like cooperative, rather than competitive, entities. Such cooperation is most likely facilitated by the fact that individuals in all bud nests are genetically related, remain in close proximity to each other, and may continue to exchange individuals after budding.

Evaluation of Liquid Baits Against Field Populations of the Longlegged Ant (Hymenoptera: Formicidae)

An evaluation of several insecticides, namely, 0.01% fipronil, 0.05% indoxacarb, and 2% boric acid in liquid bait formulations were carried out against field populations of the longlegged ant, Anoplolepis gracilipes (Fr. Smith) (Hymenoptera: Formicidae). The baits were formulated in brown cane sugar solution (50%, wt:wt) and placed in an experimental bait station. Each bait was evaluated against populations of A. gracilipes at four buildings. Fipronil, indoxacarb, and boric acid were effective against A. gracilipes, with > 90% reduction of workers within 3 d posttreatment. Total reduction (100%) was achieved within 7 d for fipronil, 14 d for indoxacarb, and 56 d for boric acid. The performance of fipronil and indoxacarb baits did not differ significantly (P > 0.05) in all postbaiting sampling intervals. Reduction of A. gracilipes resulted in an increase in other ant species [Monomorium pharaonis (L.), Monomorium floricola (Jerdon), Monomorium orientale Mayr, Monomorium destructor (Jerdon), Tapinoma indicum Forel, Pheidole sp., and Camponotus sp.] at the baited locations.

Aggression, cooperation, and relatedness among colonies of the invasive ant, Monomorium pharaonis, originating from different areas of the world

The cooperation and aggression between five laboratory colonies of Monomorium pharaonis were compared using an aggressiveness test and pupa-carrying test in laboratory arenas. The colonies were derived from field collections in different parts of Europe and USA. Generally, inter-colony aggressiveness was low and acceptance of pupae from other colonies was high. Workers from one colony (Lužiny, CZ), however, frequently displayed aggressive behavior when paired with workers from other colonies, and the Lužiny pupae were avoided by workers of other colonies in pupa-carrying tests. Behavioral tests were only partly consistent with the phylogenetic relatedness of ants because the Wisconsin colony (USA) grouped with the Lužiny colony (and not with the other three colonies) in the phylogenetic analysis but grouped with the other three colonies in the behavioral tests.

Evaluation of the possible role of ants (Hymenoptera: Formicidae) as mechanical vectors of nematodes and protists

Nematodes and protists can be transmitted to humans in many ways and little concern has been given to the mechanical transmission by ants. This study aimed at analysing how the eggs of Ascaris lumbricoides and cysts of Entamoeba coli could be mechanically transmitted to the man by Formicidae. Through the experiments using nests of Tapinoma melanocephalum, Linepithema humile and Monomorium pharaonis reared in the laboratory allied to observations of some 17 ant species in an urban park area in Mogi das Cruzes (SP), it was found that L. humile was capable of carrying eggs of A. lumbricoides both in the field and laboratory conditions (1 worker), as well as was Camponotus rufipes (2), Solenopsis saevissima (1) and Acromyrmex niger (1). The cysts of Escherichia coli were found over three workers of C. rufipes. Although the frequency of the workers found transporting pathogens was low, the capacity of common household species in carrying pathogens like nematodes and protists was demonstrated.

An agent-based model to investigate the roles of attractive and repellent pheromones in ant decision making during foraging

Pharaoh's ants organise their foraging system using three types of trail pheromone. All previous foraging models based on specific ant foraging systems have assumed that only a single attractive pheromone is used. Here we present an agent-based model based on trail choice at a trail bifurcation within the foraging trail network of a Pharaoh's ant colony which includes both attractive (positive) and repellent (negative) trail pheromones. Experiments have previously shown that Pharaoh's ants use both types of pheromone. We investigate how the repellent pheromone affects trail choice and foraging success in our simulated foraging system. We find that both the repellent and attractive pheromones have a role in trail choice, and that the repellent pheromone prevents random fluctuations which could otherwise lead to a positive feedback loop causing the colony to concentrate its foraging on the unrewarding trail. An emergent feature of the model is a high level of variability in the level of repellent pheromone on the unrewarding branch. This is caused by the repellent pheromone exerting negative feedback on its own deposition. We also investigate the dynamic situation where the location of the food is changed after foraging trails are established. We find that the repellent pheromone has a key role in enabling the colony to refocus the foraging effort to the new location. Our results show that having a repellent pheromone is adaptive, as it increases the robustness and flexibility of the colony's overall foraging response.

Decay rates of attractive and repellent pheromones in an ant foraging trail network

Pharaoh's ants (Monomorium pharaonis) use at least three types of foraging trail pheromone: a long-lasting attractive pheromone and two short-lived pheromones, one attractive and one repellent. We measured the decay rates of the behavioural response of ant workers at a trail bifurcation to trail substrate marked with either repellent or attractive short-lived pheromones. Our results show that the repellent pheromone effect lasts more than twice as long as the attractive pheromone effect (78 min versus 33 min). Although the effects of these two pheromones decay at approximately the same rate, the initial effect of the repellent pheromone on branch choice is almost twice that of the attractive pheromone (48% versus 25% above control). We hypothesise that the two pheromones have complementary but distinct roles, with the repellent pheromone specifically directing ants at bifurcations, while the attractive pheromone guides ants along the entire trail.

The Effects of Invasive Ants on the Nesting Success of Tristram's Storm-petrel, Oceanodroma tristrami, on Laysan Island, Hawaiian Islands National Wildlife Refuge

The possible impact of invasive ants on the avifauna of the Northwest Hawaiian Islands was investigated by studying the breeding success of Tristram's Storm-petrel Oceanodroma tristrami on Laysan Island. The tramp ant Monomorium pharaonis (L.) was found to be abundant in storm-petrel nesting areas on Laysan Island. There were 380 observations made on incubating adults and 798 observations for chicks, for a total of 1178 observations from 116 storm-petrel nest sites. No ant harassment events involving incubating adult storm-petrels were recorded. Thirteen instances of more than 5 ants on Tristram's Storm-petrel chicks were recorded. One harassment event was recorded, involving approximately 200 ants. The chick left the nest site immediately following the event, did not return, and presumably died. The number of nest failures attributed to M. pharaonis was 1% (n = 116). There was a significant relationship between nest type and ant interactions (G = 24.45, p = <0.0001, n =55), with incidents only recorded from birds nesting under vegetation. It was hypothesized that the ant interactions recorded in this study were a result of Tristram's Storm-petrel chicks being in close proximity to M. pharaonis nests rather than direct predation. Thus no evidence was found of a severe impact of invasive ants on the breeding success of storm-petrels at Laysan Island. Despite no direct ant impact particular attention should be given to the interactions between M. pharaonis and bird species reliant on vegetation for nesting cover, and studies therefore should include additional breeding bird species.

Ant communities (Hymenoptera: Formicidae) in an urban ecosystem near the Atlantic Rainforest

The relationships between an urban ecosystem located near the Atlantic Rainforest in southeastern Brazil and ant communities were studied with the objective of quantifying the ant richness and abundance in the household environment and its surroundings. Eighty residences were sampled, where 58 species and 28 genera pertaining to 7 sub-families were found to be present. Inside the residences, the species richness was found to be lower (26), although the abundance was greater (10,670), with the wash area and kitchen being the locales that contributed with the greatest number of hits. The opposite was true in the areas outside the residences, where 54 species and 3,747 ants were observed. Inside houses, the species known as Tramp ants were found, in the following order of importance: Solenopsis saevissima, Tapinoma melanocephalum, Linepithema humile, Paratrechina fulva, Wasmannia auropunctata, P. longicornis, Pheidole megacephala, Monomorium pharaonis and M. floricola. Externally, mainly in the yards and gardens, species such as Octostruma rugifera, Heteroponera dolo, Hypoponera sp.1 and sp.6, Gnamptogenys sp. 4, G. striatula, Odontomachus meinerti, Pachycondyla constricta and P. striata were found. In general, a greater number of species and lower abundance of individuals were observed in the neighborhoods nearer the mountains than in those closer to the urban center.

Modulation of pheromone trail strength with food quality in Pharaoh's ant, Monomorium pharaonis

Pheromone trails are self-organized processes, where colony-level behaviour emerges from the activity of many individuals responding to local information. The Pharaoh's ant is an important model species for investigating pheromone trails. Here we show that Pharaoh's ant foragers mark with trail pheromones, using their stinger, on both the outward and return leg of foraging trips. Examination of trail markings showed that 10.5% of returning fed ants simply made marks by dragging their engorged gaster, because stinger marks were absent. After discounting gaster-dragging hair marks we found that fed ants (42.5%) did not mark significantly more frequently than unfed ants (36.0%). However, we found that trail-marking fed ants marked pheromone trails with a significantly greater intensity, as compared to trail-marking unfed ants, if the food source was high quality (1.0 M sucrose). When the food quality was low (0.01 M sucrose) we detected no significant difference in marking intensity between fed and unfed trail-marking ants. Our results show that in Pharaoh's ants individual trail marking occurs at a frequency of ∼40% among fed and unfed foragers, but the frequency of individuals marking with high intensity (continuous marking) is significantly greater when a food source is high quality. This contrasts with another model species, Lasius niger, where trail strength is modulated by an all-or-nothing individual response to food quality. The reason for this fundamental difference in mechanism is that Pharaoh's ant is highly reliant on pheromone trails for environmental orientation, so must produce trails, whereas L. niger is proficient at visual-based orientation.

Detection and Quantification of Pharaoh Ant Antigens in Household Dust Samples as Newly Identified Aeroallergens

Background:The widespread house ant, Monomorium pharaonis (pharaoh ant, PA), was recently identified as a potential cause of respiratory allergies. However, there are no reports of the distribution of PA allergens in various environments. We developed specific ELISA inhibition assays and measured the distribution and amount of PA antigens in household dust samples. Methods:Floor dust was collected at 3-month intervals from 56 homes in Seoul over a 1-year period. PA antigens in fine dusts were quantified by ELISA inhibition assays using rabbit anti-PA sera, and specific IgE to PA antigens in residents’ serum was measured by ELISA. Results: In 18 of the 56 homes (32.1%), PA antigen was detected in at least 1 floor dust sample either from the living room or the kitchen. Levels of PA antigens showed seasonal variations with peaks in autumn and winter. The detection rate of PA antigens was significantly higher in homes with visual evidence of PA infestations (70%) than in homes without such infestations (23.9%; p < 0.05). However, a significant amount of PA antigens was still detected in uninfested homes. Thirteen of 113 (11.5%) residents were positive for PA-specific IgE. PA-specific IgE was detected more frequently in residents living in PA antigen-positive homes (19.6%) than in antigen-negative homes (4.8%; p < 0.05). Conclusion: A considerable level of PA antigens is distributed in the indoor environment. Therefore, inhalant exposure to PA antigens can occur during domestic activities. These results suggest that PAs might be a significant source of aeroallergens in households.