Tropical Fire Research Articles

Revealing the pH-dependent conformational changes in sol g 2.1 protein and potential ligands binding

Sol g 2, a major protein found in the venom of the tropical fire ant (Solenopsis geminata), is well-known for its ability to bind various hydrophobic molecules. In this study, we investigate the binding activity of recombinant Sol g 2.1 protein (rSol g 2.1) with potential molecules, including (E)-β-Farnesene, α-Caryophyllene, and 1-Octen-3-ol at different pH levels (pH 7.4 and 5.5) using fluorescence competitive binding assays (FCBA). Our results revealed that Sol g 2.1 protein has higher affinity binding with these ligands at neutral pH. Relevance to molecular docking and molecular dynamics simulations were utilized to provide insights into the stability and conformational dynamics of Sol g 2.1 and its ligand complexes. After simulation, we found that Sol g 2.1 protein has higher affinity binding with these ligands as well as high structural stability at pH 7.4 than at an acidic pH level, indicating by RMSD, RMSF, Rg, SASA, and principal component analysis (PCA). Additionally, the Sol g 2.1 protein complexes at pH 7.4 showed significantly lower binding free energy (∆Gbind) and higher total residue contributions, particularly from key non-polar amino acids such as Trp36, Met40, Cys62, and Ile104, compared to the lower pH environment. These explain why they exhibited higher binding affinity than the lower pH. Therefore, we suggested that Sol g 2.1 protein is a pH-responsive carrier protein. These findings also expand our understanding of protein–ligand interactions and offer potential avenues for the development of innovative drug delivery strategies targeting Sol g 2.1 protein.

When to monitor or control: Informed invasive species management using a partially observable Markov decision process (POMDP) framework

Abstract Resource allocation for invasive species management requires information about the size of the invasive population, which may be expensive and time‐consuming to obtain. The trade‐off between investment in monitoring and control efforts is a challenging decision problem, and existing mathematical tools are often difficult to interpret, and/or limited to a specific case study. We propose a partially observable Markov decision process (POMDP) framework to help decision‐makers understand effective monitoring and control policymaking. POMDPs can deal with uncertainty in both the model and state of the system but are more challenging to solve due to the continuous and high‐dimensional state space. Rather than limiting the possible states of the system, as do most previously proposed methods, we work through the development of a density projection approach, which reduces the dimensionality of the space of beliefs by restricting them to a parametrised family of probability distributions. This serves to align the mathematical representation of the problem with the real‐world quantities relevant to human decision‐making. The result of our model is a sequence of actions, which minimises the expected cost incurred in managing the invasive species, where the recommendation depends on an estimate of the species' abundance, and the uncertainty in this estimate. We demonstrate the effectiveness of our proposed framework with a case study on tropical fire ant (Solenopsis geminata) control and two generic case studies of varying complexity. Furthermore, we investigate sensitivity of the results to the choices of control cost and efficacy, and monitoring cost and error. The framework proposed by this paper makes the powerful machinery of POMDPs available to environmental managers. It computes the optimal course of action to manage a growing population of an invasive species, incorporating a varying time horizon and multiple control interventions. We sidestep the computational difficulties of general POMDPs to provide a clear, visual overview of decision‐making recommendations, and how these decisions change in new situations. Initial results and scenario‐based analysis show promising results, and the framework could be extended to the related field of disease management.

Structure-based epitope prediction and assessment of cross-reactivity of Myrmecia pilosula venom-specific IgE and recombinant Sol g proteins (Solenopsis geminata)

The global distribution of tropical fire ants (Solenopsis geminata) raises concerns about anaphylaxis and serious medical issues in numerous countries. This investigation focused on the cross-reactivity of allergen-specific IgE antibodies between S. geminata and Myrmecia pilosula (Jack Jumper ant) venom proteins due to the potential emergence of cross-reactive allergies in the future. Antibody epitope analysis unveiled one predominant conformational epitope on Sol g 1.1 (PI score of 0.989), followed by Sol g 2.2, Sol g 4.1, and Sol g 3.1. Additionally, Pilosulin 1 showed high allergenic potential (PI score of 0.94), with Pilosulin 5a (PI score of 0.797) leading in B-cell epitopes. The sequence analysis indicated that Sol g 2.2 and Sol g 4.1 pose a high risk of cross-reactivity with Pilosulins 4.1a and 5a. Furthermore, the cross-reactivity of recombinant Sol g proteins with M. pilosula-specific IgE antibodies from 41 patients revealed high cross-reactivity for r-Sol g 3.1 (58.53%) and r-Sol g 4.1 (43.90%), followed by r-Sol g 2.2 (26.82%), and r-Sol g 1.1 (9.75%). Therefore, this study demonstrates cross-reactivity (85.36%) between S. geminata and M. pilosula, highlighting the allergenic risk. Understanding these reactions is vital for the prevention of severe allergic reactions, especially in individuals with pre-existing Jumper Jack ant allergy, informing future management strategies.

Demise and Recolonization by the Tropical Fire Ant and Other Ants (Hymenoptera: Formicidae) in a Melon Field in Mexico

Demise and Recolonization by the Tropical Fire Ant and Other Ants (Hymenoptera: Formicidae) in a Melon Field in Mexico

ENSO‐Related Fire Weather Changes in Southeast and Equatorial Asia: A Quantitative Evaluation Using Fire Weather Index

AbstractInterannual variability of tropical fire activity has been linked to the El Niño‐Southern Oscillation (ENSO). Here we analyze changes in fire and simultaneous fire weather related to ENSO over Southeast (SEAS) and Equatorial Asia (EQAS) and quantitively evaluate the contribution of key meteorological variables to the fire weather variations for the past decades. During the fire seasons, large increases in fires emerge in El Niño years, which greatly coincides with the more fire‐susceptible weather conditions compared to La Niña years. Moreover, the fires exhibit a more significant correlation with the ENSO index in El Niño years, mainly due to the influence of asymmetry response of the fire weather to ENSO. Composite analysis shows that it is the positive anomalous low‐level geopotential height and less water vapor transportation over SEAS (March–May) and EQAS (August–October) during El Niño that forms the fire‐favoring weather. By conducting tests in calculating fire weather index (FWI) under different ideal conditions, we identified the daily precipitation as the dominant driver of FWI variation, with the contribution reaching 65.5%–77.5% and 60.9%–90.5% for SEAS and EQAS respectively, while decreased relative humidity induces nearly a quarter of increases in FWI in El Niño years. Changes in temperature and wind speed, however, rarely perturb the fire weather for both SEAS and EQAS regions. The quantitative evaluations of individual meteorological variables in shaping fire weather as well as their asymmetrical response in ENSO years could support fire management during fire seasons in Tropical Asia.

First report on the tropical fire ant, Solonopsis geminate (Fabricius) as flower damaging pest of moringa (Moringa oleifera Lam.) cultivated near the Western Ghats of Dindigul, Tamil Nadu.

First report on the tropical fire ant, Solonopsis geminate (Fabricius) as flower damaging pest of moringa (Moringa oleifera Lam.) cultivated near the Western Ghats of Dindigul, Tamil Nadu.

Spread of stinging ants to oceanic islands, and the need to raise awareness of prevention and treatment of ant stings.

Venomous invasive ants are rapidly dispersing throughout oceanic islands. Medics unfamiliar with envenomation or venom-induced anaphylaxis may be unprepared for the range of possible reactions and corresponding treatments. We detail the suboptimal treatment of a patient suffering anaphylaxis from an ant sting on a remote island and describe what treatment should have been provided. The patient experienced stings on his feet from an ant later identified as tropical fire ant, Solenopsis geminata. Clinical examination revealed throat swelling without obstruction of the airway or pharynx. The patient was provided the following suboptimal treatment: intravenously-administered antihistamine and saline perfusion. Injected epinephrine should be the standard first line of treatment for anaphylaxis, even when not all symptoms are present. A rise in invasive hymenopteran stings on oceanic islands is inevitable, and proactively improving public awareness and medical training could save lives.

Winged insects associated with the poorly studied forest fire ant Solenopsis virulens (Hymenoptera: Formicidae)

The present study documents new records of winged insects collected from fragments of nests of the tropical fire ant Solenopsis virulens (Smith), using a trap, which is also described in detail. The emergence chamber consisted of a 5L opaque plastic container, a 50 ml transparent vial and a 1.5 ml microcentrifuge tube. This trap captured 70 insects from 12 nests of Solenopsis virulens. They were classified into two orders, 13 families, 18 genera and 39 morphospecies. The most abundant order was Diptera, with nine families. The richest family was Cecidomyiidae, with 12 morphospecies, followed by Sciaridae with seven. Ceratopogonidae, Chironomidae, Chloropidae, Drosophilidae, Hybotidae, Phoridae and Psychodidae were also represented. Hymenoptera included a total of three families: Figitidae (Eucoilinae), Platygastridae (Scelioninae and Platygastrinae) and Diapriidae. Although the association of several genera (Diptera: 11/ Hymenoptera: 1) and families (Diptera: 1/ Hymenoptera: 1) with ant nests was recorded for the first time, it is likely that many of these insects are only fortuitous or temporary inquilines and not obligatory myrmecophiles. The trap described is also useful for catching insects that emerge from other substrates such as leaves, logs, galls, termite nests, etc. Furthermore, it could enable researchers to sample and further study important material in the laboratory and decrease the costs of sampling during field trips.

A compound event-oriented framework to tropical fire risk assessment in a changing climate

Tropical fire activity closely follows the co-occurrence of multiple climate stressors. Yet, it remains challenging to quantify how changes in climate alter the likelihood of fire risks associated with compound events. Recent abrupt changes in fire regimes in iconic landscapes in Brazil (namely the Pantanal and Xingu) provide a key opportunity to evaluate how extremely dry and hot conditions, both together and individually, have influenced the probability of large fires. Here we quantify the relationships between climate and fire across these regions and provide evidence on the extent to which fire risk and the associated impacts could be constrained if anthropogenic global warming is limited. We investigate the burned area, differentiating between fire types according to land use (forest fires, savanna fires, farming fires and grassland and wetland fires), and derive present and future fire risks linked to multiple climate variables. We show that concurrent air dryness (high vapour-pressure deficit (VPD)) and low precipitation have driven fire occurrence in both Xingu and the Pantanal, with VPD playing a dominant role. Historical climatic change has already increased compound event-related (CE-related) fire risks of all fire types (5%–10%), and these risks are likely to increase in the future due to global warming. The likelihood of CE-related increase in fire risk may be reduced by up to 14.4% if global warming is constrained to +1.5 °C instead of +3 °C. Nevertheless, substantially increased CE-related fire risks are still expected even if restricting global mean warming to 1.5 °C, particularly in the Pantanal. We thus conclude that climate action should be coordinated with environmental protection to reduce ignition sources and promote effective conservation measures to preserve these biomes.

Madagascar's fire regimes challenge global assumptions about landscape degradation.

Narratives of landscape degradation are often linked to unsustainable fire use by local communities. Madagascar is a case in point: the island is considered globally exceptional, with its remarkable endemic biodiversity viewed as threatened by unsustainable anthropogenic fire. Yet, fire regimes on Madagascar have not been empirically characterised or globally contextualised. Here, we contribute a comparative approach to determining relationships between regional fire regimes and global patterns and trends, applied to Madagascar using MODIS remote sensing data (2003-2019). Rather than a global exception, we show that Madagascar's fire regimes are similar to 88% of tropical burned area with shared climate and vegetation characteristics, and can be considered a microcosm of most tropical fire regimes. From 2003-2019, landscape-scale fire declined across tropical grassy biomes (17%-44% excluding Madagascar), and on Madagascar at a relatively fast rate (36%-46%). Thus, high tree loss anomalies on the island (1.25-4.77× the tropical average) were not explained by any general expansion of landscape-scale fire in grassy biomes. Rather, tree loss anomalies centred in forests, and could not be explained by landscape-scale fire escaping from savannas into forests. Unexpectedly, the highest tree loss anomalies on Madagascar (4.77×) occurred in environments without landscape-scale fire, where the role of small-scale fires (<21 h [0.21 km2 ]) is unknown. While landscape-scale fire declined across tropical grassy biomes, trends in tropical forests reflected important differences among regions, indicating a need to better understand regional variation in the anthropogenic drivers of forest loss and fire risk. Our new understanding of Madagascar's fire regimes offers two lessons with global implications: first, landscape-scale fire is declining across tropical grassy biomes and does not explain high tree loss anomalies on Madagascar. Second, landscape-scale fire is not uniformly associated with tropical forest loss, indicating a need for socio-ecological context in framing new narratives of fire and ecosystem degradation.

Remote Sensing-Based Assessment of How Much Tropical Wetland Fires Contribute to Carbon Emissions and How Fast the Carbon Recovering Is

This research had two objectives. The first objective was to quantity the carbon emissions from fires of various types of tropical wetland vegetation using Sentinel-2 imagery. The second objective was to measure how long the carbon stock will recover using Sentinel-2 imagery. Burned areas were extracted automatically using the Relativized Burn Ratio (RBR). Calculation of carbon emissions and carbon sequestrations were carried out by measuring the differences in Above Ground Biomass (AGB) before the fires, right after the fires, and a few months after the vegetation re-grows after the fires. Therefore, multitemporal Sentinel-2 MSI imageries from three different times are required. All imageries processing was carried out using the ESA SNAP software. The results showed that tropical wetland fires emited an average of 121.61 Mg C/ha, or equivalent to 445.9 Mg CO&lt;sub&gt;2&lt;/sub&gt;/ha. Furthermore, tropical wetlands had an average rate of about 9.27 months to restore their carbon stocks to their pre-burnt state. Peatland forests took the longest time to recover to its original carbon stock state after burning, which was almost 22 years to recover.

Searching Behavior in the Tropical Fire Ant Solenopsis geminata (Hymenoptera: Formicidae).

Social insects have evolved different search strategies to find target objects in unknown environments. In the present study, the searching behavior of the tropical fire ant Solenopsis geminata was investigated in a circular arena. The average time, search path, speed, and search patterns of worker ants in a circular arena were determined. The results showed that fire ant workers followed six major search patterns. The variation in the searching patterns of workers may explain the different levels of exploration. Most workers (56.8%) tended to search in small loops and progressively increase the search area size. These workers mostly turned in one direction, either clockwise or counterclockwise. More workers turned in a consistent pattern than in an inconsistent pattern. Moving speed was also higher in workers that maintained their turning directions than in those that changed directions. We thus propose that following search patterns consisting of loops of increasing size may be an effective strategy. The tropical fire ant S. geminata is a globally invasive species that was introduced to Taiwan 40 years ago and has continued to threaten residents. Based on behavioral studies of S. geminata, we may gain a better understanding of their exploratory behavior in the ecosystem in Taiwan.

Isotopic signatures of methane emissions from tropical fires, agriculture and wetlands: the MOYA and ZWAMPS flights.

We report methane isotopologue data from aircraft and ground measurements in Africa and South America. Aircraft campaigns sampled strong methane fluxes over tropical papyrus wetlands in the Nile, Congo and Zambezi basins, herbaceous wetlands in Bolivian southern Amazonia, and over fires in African woodland, cropland and savannah grassland. Measured methane δ13CCH4 isotopic signatures were in the range −55 to −49‰ for emissions from equatorial Nile wetlands and agricultural areas, but widely −60 ± 1‰ from Upper Congo and Zambezi wetlands. Very similar δ13CCH4 signatures were measured over the Amazonian wetlands of NE Bolivia (around −59‰) and the overall δ13CCH4 signature from outer tropical wetlands in the southern Upper Congo and Upper Amazon drainage plotted together was −59 ± 2‰. These results were more negative than expected. For African cattle, δ13CCH4 values were around −60 to −50‰. Isotopic ratios in methane emitted by tropical fires depended on the C3 : C4 ratio of the biomass fuel. In smoke from tropical C3 dry forest fires in Senegal, δ13CCH4 values were around −28‰. By contrast, African C4 tropical grass fire δ13CCH4 values were −16 to −12‰. Methane from urban landfills in Zambia and Zimbabwe, which have frequent waste fires, had δ13CCH4 around −37 to −36‰. These new isotopic values help improve isotopic constraints on global methane budget models because atmospheric δ13CCH4 values predicted by global atmospheric models are highly sensitive to the δ13CCH4 isotopic signatures applied to tropical wetland emissions. Field and aircraft campaigns also observed widespread regional smoke pollution over Africa, in both the wet and dry seasons, and large urban pollution plumes. The work highlights the need to understand tropical greenhouse gas emissions in order to meet the goals of the UNFCCC Paris Agreement, and to help reduce air pollution over wide regions of Africa.This article is part of a discussion meeting issue 'Rising methane: is warming feeding warming? (part 2)'.

Hurricanes as an enabler of Amazon fires

A teleconnection between North Atlantic tropical storms and Amazon fires is investigated as a possible case of compound remote extreme events. The seasonal cycles of the storms and fires are in phase with a maximum around September and have significant inter-annual correlation. Years of high Amazon fire activity are associated with atmospheric conditions over the Atlantic which favour tropical cyclones. We propose that anomalous precipitation and latent heating in the Caribbean, partly caused by tropical storms, leads to a thermal circulation response which creates anomalous subsidence and enhances surface solar heating over the Amazon. The Caribbean storms and precipitation anomalies could thus promote favourable atmospheric conditions for Amazon fire.

Predicting the Global Distribution of Solenopsis geminata (Hymenoptera: Formicidae) under Climate Change Using the MaxEnt Model.

Simple SummaryClimate change influences the distribution of species. The tropical fire ant Solenopsis geminata (Hymenoptera: Formicidae) is a serious invasive species that damages the native ecosystem. In this study, we evaluated the current and future distribution of S. geminata under climate change using the ecological niche model. The model results showed that the favorable habitat area of S. geminata will expand to higher latitudes on a global scale due to future global warming. Some countries located in America and East Asia, such as Brazil, China, South Korea, the USA, and Uruguay, can be threatened by S. geminata due to climate change.The tropical fire ant Solenopsis geminata (Hymenoptera: Formicidae) is a serious invasive species that causes a decline in agricultural production, damages infrastructure, and harms human health. This study was aimed to develop a model using the maximum entropy (MaxEnt) algorithm to predict the current and future distribution of S. geminata on a global scale for effective monitoring and management. In total, 669 occurrence sites of S. geminata and six bioclimatic variables of current and future climate change scenarios for 2050 and 2100 were used for the modeling. The annual mean temperature, annual precipitation, and precipitation in the driest quarter were the key influential factors for determining the distribution of S. geminata. Although the potential global distribution area of S. geminata is predicted to decrease slightly under global warming, the distribution of favorable habitats is predicted to expand to high latitudes under climate scenarios. In addition, some countries in America and East Asia, such as Brazil, China, South Korea, the USA, and Uruguay, are predicted to be threatened by S. geminata invasion under future climate change. These findings can facilitate the proactive management of S. geminata through monitoring, surveillance, and quarantine measures.

Satellite Observations of the Tropical Terrestrial Carbon Balance and Interactions With the Water Cycle During the 21st Century

AbstractA constellation of satellites is now in orbit providing information about terrestrial carbon and water storage and fluxes. These combined observations show that the tropical biosphere has changed significantly in the last 2 decades from the combined effects of climate variability and land use. Large areas of forest have been cleared in both wet and dry forests, increasing the source of carbon to the atmosphere. Concomitantly, tropical fire emissions have declined, at least until 2016, from changes in land‐use practices and rainfall, increasing the net carbon sink. Measurements of carbon stocks and fluxes from disturbance and recovery and of vegetation photosynthesis show significant regional variability of net biosphere exchange and gross primary productivity across the tropics and are tied to seasonal and interannual changes in water fluxes and storage. Comparison of satellite based estimates of evapotranspiration, photosynthesis, and the deuterium content of water vapor with patterns of total water storage and rainfall demonstrate the presence of vegetation‐atmosphere interactions and feedback mechanisms across tropical forests. However, these observations of stocks, fluxes and inferred interactions between them do not point unambiguously to either positive or negative feedbacks in carbon and water exchanges. These ambiguities highlight the need for assimilation of these new measurements with Earth System models for a consistent assessment of process interactions, along with focused field campaigns that integrate ground, aircraft and satellite measurements, to quantify the controlling carbon and water processes and their feedback mechanisms.

Development of a predictive model for soil temperature and its application to species distribution modeling of ant species in South Korea

Soil temperature is an important factor for determining ant species inhabitation, but it has rarely been applied in species distribution modeling due to limited data sources. Hence, this study aimed to develop a predictive model for soil temperature and evaluate the potential distribution of a few ant species in South Korea. The monthly maximum and minimum soil temperatures were predicted by linear regression as a function of the monthly maximum and minimum air temperatures. Then, the developed model was used to predict the potential distribution of the tropical fire ant (Solenopsis geminata Fabricius; TFA), red imported fire ant (Solenopsis invicta Buren; RIFA), and yellow crazy ant (Anoplolepis gracilipes Smith; YCA). Three ant species were selected because they have globally exerted negative impacts on the ecology of the invading area. The developed model could predict soil temperatures at 5, 10, 20, and 30 cm deep with an R2 value of 0.95. The climate suitability of TFA, RIFA, and YCA, predicted by soil temperature in the CLIMEX model, was found to be up to 25, 12, and 65 times higher than the climate suitability predicted by air temperature, respectively. This study showed that the potential distribution predicted based on air and soil temperature could be different for a species inhabiting the ground, suggesting that it is necessary to consider not only the outside environment, but also the soil environment, for an accurate prediction.

Beyond slash‐and‐burn: The roles of human activities, altered hydrology and fuels in peat fires in Central Kalimantan, Indonesia

Near‐annual landscape‐scale fires in Indonesia's peatlands have caused severe air pollution, economic losses, and health impacts for millions of Southeast Asia residents. While the extent of fires across the peatland surface has been widely attributed to widespread peatland drainage for plantation agriculture, fires that transition from surface into sub‐surface soil‐based fires are the source of the most dangerous air pollution. Yet the mechanisms by which this transition occurs have rarely been considered, particularly in diversely managed landscapes. Integrating physical geography methods, including active fire scene evaluations and hydrological monitoring, with qualitative methods such as retrospective fire scene evaluations and semi‐structured interviews, this article discusses how and why sub‐surface peat fire transition occurs in an intensively altered peatland ecosystem in Indonesia's Central Kalimantan province. We demonstrate that variable water table levels and flammable surface vegetation (fire fuels) are co‐produced socio‐political and biophysical phenomena that enable the conditions in which surface fire is likely to transition into peat fire and increase landscape vulnerability to ongoing, uncontrollable annual fires. This localized understanding of peat fire transition counters normative causal narratives of tropical fire such as ‘slash‐and‐burn’, with implications for the management of new fire regimes in inhabited landscapes.

Model-based assessment of changes in the potential distribution of Solenopsis geminata (Hymenoptera: Formicidae) according to climate change scenarios

The tropical fire ant (TFA, Solenopsis geminata) is an aggressive fire ant species that can cause health problems in humans and damages ecosystems. The TFA can be found across the world, from North and South America to Africa, Asia, and Oceania; furthermore, it has been introduced into new areas by human transport or natural flights. In this study, species distribution modeling was applied to the TFA for the first time, and its potential distribution as a response to climate change was evaluated. This study used CLIMEX as the climate-specific species distribution modeling tool with the distribution data for TFA, current global meteorological data, and two types of climate change scenarios. Thus, although the climatic suitability of the TFA was assumed to decrease with climate change, its distribution limit was expected to increase. In addition, the difference between potential distributions predicted using Special Report on Emissions Scenarios A1B and Special Report on Emissions Scenarios A2 increased over time. In conclusion, even with an overall decrease in climatic suitability, in the future, the TFA will still be able to invade a new area that it cannot inhabit under the current climatic scenario. As the first study that predicts TFA distribution using a species distribution model, we expect that this study will provide the basic information for further TFA modeling and for setting up quarantine and control measures.

Carriers and cutters: size-dependent caste polyethism in the tropical fire ant (Solenopsis geminata).

Body size is an important life-history trait in eusocial insects which plays a key role in colony fitness. The division of labour, represented by caste polyethism, correlates with divergent morphological traits. Size polymorphism has been noted in the tropical fire ant, Solenopsis geminata; however, little is known regarding the differences in the size distributions of workers performing foraging tasks. In the present study, task partitioning was observed in the foraging activities of S. geminata. Two subgroups among foraging workers of S. geminata were discovered using the Gaussian mixture model: a large worker group (head width ≥ 0.924 mm) and a small worker group (head width < 0.924 mm). The foraging worker population comprised two distinct groups - 25.64% were large workers and 74.36% were small workers. Larger workers delivered heavier seeds faster than smaller workers, but this difference became less apparent when lighter seeds were being carried. When large prey such as crickets was encountered during foraging, S. geminata partitioned their tasks into cutting and transportation. The large workers were observed to cut cricket prey into fragments with their longer mandibles, and the small workers then transported these fragments back to the nest. These results present evidence of task partitioning among tropical fire ants, with different tasks being performed by ants of different castes.