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Can foraging worker ants become queens?

Can foraging worker ants become queens?



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The TL;DR is in the subject line.

The back story is as follows:

I am combating ants in my high-rise apartment unit. One piece of online advice was to vacuum regularly, and pay attention to edges of the floor. I'm considering taping up the vacuum bag opening so that I'm not tossing out a nearly empty bag every day (almost $10 each, and terrible for the environment).

I had initial concern that an ant might get out, so I also double bagged the vacuum bag. This is making it inconvenient to use, meaning that I'll vacuum less. Exactly the opposite of the online advice.

I think that the chances of an ant getting out is low, and even if escape was possible, it probably wouldn't be more than one or two. I can accept that, if they don't go start generating more ants.

I haven't found anything online about workers being able to transform into queens once they are foraging. What I have read is that it has to do with genetics and extra nutrition during the formative stages.

Is it safe to assume that foraging workers will not be able to turn into queens?

After note: It just occurred to me, if ants can chew through wood, then there's nothing to prevent them from chewing through a vacuum bag over the course of a day or more. They can even chew through the plastic bag in which the vacuum bag is sealed. Is this a valid concern, or is their ability to chew limited to wood?


Workers cannot become "queens" because the development of a larvae into a worker or a queen happens during the larval stage, depending mainly on the food that the larvae is given. That being said, once the queen is removed from a colony, in many ant and other social hymenopteran species, workers are no longer inhibited by the pheromones produced by the queens that prevent the growth of the worker's ovaries. So in some species, removing the queen can lead to workers laying eggs but these will most often be parthenogenetic and lead to the production of males only. In a very few species, workers can produce female eggs by parthenogenesis or mate with males after the removal of the queen. Such traits are usually associated with large body size and small colony size, so they are unlikely to be the ones you have in buildings.

Bourke, A. F. (1988). Worker reproduction in the higher eusocial Hymenoptera. The Quarterly Review of Biology, 63(3), 291-311.

Page, R. E., & Erickson, E. H. (1988). Reproduction by worker honey bees (Apis mellifera L.). Behavioral Ecology and Sociobiology, 23(2), 117-126.

Wenseleers, T., Helanterä, H., Hart, A., & Ratnieks, F. L. (2004). Worker reproduction and policing in insect societies: an ESS analysis. Journal of evolutionary biology, 17(5), 1035-1047.


This Ant Can Shrink and Regrow Its Brain

In most species of ants, the colony only has one queen and royal status is conferred at birth. But Indian jumping ants (Harpegnathos saltator) offer members of a colony’s sterile, submissive worker caste a chance at a twisted fairy tale.

Among these ants, if the queen meets an untimely end, there is a fleeting chance for a few of the plebeians to make a sudden Cinderella-like ascension to royalty. To change their fate, the workers must win a series of jousting matches against rivals using their antenna to parry and jab at the competition.

When the battle, which can last up to 40 days, concludes, a handful of the most successful combatants begin growing huge functional ovaries that will allow them to begin laying eggs. The bizarre catch is the winning ants also lose nearly a fifth of their brain mass on their way to becoming pseudo-queens.

But new research finds that, incredibly, if the cloistered, egg-laying life of ant royalty doesn’t work out, the pseudo-queens can revert to the lives of commoners and regrow that lost brain tissue, reports Annie Roth for the New York Times. The research, published this week in the journal the Proceedings of the Royal Society B, is the first known instance of an insect losing and regaining brain size.

“Traditionally, people think that once neural tissue is gone, it doesn't come back,” says Clint Penick, a biologist at Kennesaw State and the study’s lead author, in a statement. “But we found that when workers of the Indian jumping ant switch caste roles, they can both lose and regrow large regions of their brains. Future understanding of the mechanisms involved in these brain changes might shed light on how brain plasticity is controlled in humans, especially with regards to helping regenerate or repair neural damage.”

To study the unique bodily transformation that the Indian jumping ant’s pseudo-queens undergo, the researchers painted a group of 60 pseudo-queens from 30 colonies with different colors to tell them apart. The researchers then separated half of the ants from their colonies and put each one in isolation, reports Troy Farah for National Geographic. The team left the other 30 pseudo-queens—also called called gamergates—with their respective subjects as a control group.

After a few days, the isolated pseudo-queens stopped laying eggs, and after a few weeks the ants began to revert to typical worker behaviors, reports Natalie Grover for the Guardian. At the six- to eight-week mark, Penick and his co-authors dissected the ants that appeared to have given up their temporary royal status and found their ovaries had shrunk back down to normal dimensions and their brains had also grown back to assume their former size.

“There are lots of insects with documented plasticity in all of the traits here—but none that I know of with this level of reversible plasticity,” Emilie Snell-Rood, an evolutionary biologist at the University of Minnesota who wasn’t involved in the research, tells National Geographic. “Many social insects show changes in these brain regions as they transition between phases of their worker life, or move from foraging behavior to queen behavior. But shifting neural investment once, and then back later, is another thing entirely.”

As for why the ants slash their processing power when they assume the throne, Penick tells the Times the pseudo-queen’s royal duties don’t take much in the way of cognitive processing power. Food is brought to them, and defending the nest is someone else’s job.

“Worker ants need a large brain to deal with these cognitive tasks, but gamergates don’t need to think that much,” Penick tells the Times. “Once they win the tournament, they become little more than egg-laying machines.”

As Penick tells the Guardian, the finding that the Indian jumping ant can regrow its brain “opens up opportunities now to dig into the mechanisms that control whether a brain region grows or shrinks in size.”


In Dueling Ants Vying to Become Replacement Queen, Behavioral and Molecular Cues Quickly Determine Who Will Win

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In one species of ants, workers duel to establish new leadership after the death of their queen. While these sparring matches stretch for more than a month, changes in behavior and gene expression in the first three days of dueling can accurately predict who will triumph, according to a New York University study published in the journal Genes & Development.

“Despite prolonged social upheaval in ant colonies following the loss of the queen, the winners of these dueling tournaments are rapidly determined,” said Claude Desplan, Silver Professor of Biology at NYU. “Our findings may provide clues on adaptability in reproduction and aging, given that the workers who win the duel, or ‘pseudoqueens,’ gain the ability to lay eggs and live much longer than the average worker ant. This suggests that changes in the environment are able to dramatically affect the structure of a society.”

The caste system in social insects creates a division of labor, with insects specialized to perform particular tasks. The queen is responsible for reproduction, while workers maintain the colony—caring for the young, foraging and hunting for food, cleaning, and defending the nest.

In many insect societies, when the queen dies, the entire colony dies along with her due to the lack of reproduction. However, in Indian jumping ants (Harpegnathos saltator), “caste switching” occurs after the queen’s death. While the queen is alive, she secretes pheromones that prevent female worker ants from laying eggs, but when she dies, the workers sense the lack of pheromones and begin fighting each other to take on the top role.

The ants engage in dueling tournaments, striking each other with their antennae in matches that can last more than a month. While most ants quickly return to their usual work during the tournament, the winners become pseudoqueens—also known as gamergates—and acquire new behaviors and roles. Through this transition, their life expectancy dramatically increases (from seven months to four years) and they begin laying eggs, allowing the colony to survive.

In their study in Genes & Development, NYU researchers explored changes in the Indian jumping ants’ social behavior and accompanying changes in gene expression during the early stages of the worker-to-pseudoqueen transition.

They found that, as early as after three days of dueling, the winners can be accurately predicted solely based on the dueling behavior. The workers who triumphed and became pseudoqueens had much higher levels of dueling—sparring roughly twice as much in the first five days—while the others who remained workers dueled less and went back to performing other tasks such as cleaning and hunting.

“Despite the fact that dueling tournaments last for several weeks, we were able to anticipate which ants would become pseudoqueens in only three days,” said Comzit Opachaloemphan, a doctoral student in the Department of Biochemistry and Molecular Pharmacology at NYU Grossman School of Medicine and one of the study’s lead authors.

Comparing biological samples and gene expression from dueling versus non-dueling ants, the researchers then determined the changes associated with the worker-to-pseudoqueen transition. Molecular analyses revealed that the brain may be driving the dueling and early caste determination in the ants, with other tissues taking cues from the brain.

The researchers found that the first genes to respond to the loss of the queen were in the brain, suggesting that the lack of queen pheromones perceived by the olfactory system affects brain neurohormonal factors. These changes in the brain then lead to altered social behavior and hormone-mediated physiological changes in other parts of the body, including the ovaries.

“Both behavioral and molecular data—especially changes in gene expression in the brain—show us that new pseudoqueens are quickly determined after a colony’s social structure has been disrupted by the loss of the queen,” said study author Danny Reinberg, the Terry and Mel Karmazin Professor in the Department of Biochemistry and Molecular Pharmacology at NYU Grossman School of Medicine, as well as an investigator for the Howard Hughes Medical Institute.

Additional study authors include co-first authors Giacomo Mancini and Nikos Konstantinides, as well as Apurva Parikh, Jakub Mlejnek, and Hua Yan. The research was supported by a Howard Hughes Medical Institute Collaborative Innovation Award (#2009005), the National Institutes of Health (R21-GM114457, R01-EY13010, R01-AG058762, and F32AG044971), EMBO (365-2014), and the Human Frontier Science Program (LT000122/2015-L).


2. Male ants are pretty much just flying sperm

Male ants have a mother but no father. Author provided

Unlike humans, with X and Y chromosomes, an ant’s sex is determined by the number of genome copies it possesses. Male ants develop from unfertilised eggs so receive no genome from a father. This means that male ants don’t have a father and cannot have sons, but they do have grandfathers and can have grandsons. Female ants, in comparison, develop from fertilised eggs and have two genome copies – one from their father and one from their mother.

Male ants function like flying sperm. Only having one genome copy means every one of their sperm is genetically identical to themselves. And their job is over quickly, dying soon after mating, although their sperm live on, perhaps for years. – essentially their only job is to reproduce.

Let them eat cake. Shutterstock


Fire Ant Biology

If you want to control fire ants, it helps to know a little about their biology. Understand fire ant biology and you will understand why baits work so well to control fire ants and why it’s important to spread bait throughout the yard (Figure 1), rather than just putting it directly on top of the mound. You will also understand why it’s so frustrating and ineffective to try to control this pest by only treating the mounds you can see. And you will learn why, no matter how good a job you do controlling fire ants, they always come back. The biology of the red imported fire ant and the black imported fire ant is similar.

Fire ants are social, colony-forming insects. Although most fire ant colonies have only one reproducing queen, multi-queen colonies are common in some areas. In addition to the queen, or queens, an established colony contains many thousands of workers, many hundreds of virgin male and female reproductives, and many thousands of eggs and immature ants. A mature fire ant colony may contain over 200,000 individuals.

Life Cycle

The eggs, which are only produced by the queen, hatch into legless larvae that must be constantly cared for by the workers. The larvae undergo four molts before entering the pupal stage, and ultimately emerging as adults.

Despite their helpless condition, the larvae make an important contribution to the welfare of the colony—older larvae are the only individuals in the colony capable of digesting solid food. Workers bring all solid food particles to the older larvae, and, after this solid food is digested by the larvae, the resulting liquid is distributed to all members of the colony. Unlike honeybee colonies, fire ant colonies do not contain any physical structures for storing food. Food is stored inside the ants themselves, especially in the crops of larger workers.

Fire ant workers vary greatly in size. There is some task specialization, with larger workers more commonly performing certain tasks such as foraging and food storage, while smaller workers most commonly tend brood, but there is also considerable overlap, especially among medium sized workers. Reproductive females and males are considerably larger than even the largest workers. Reproductive males are darker than females and have much smaller heads.

Mound Construction

Workers build mounds by tunneling through the soil to form a honeycombed maze of tunnels. They pile the excavated soil immediately above the soil line and form tunnels in this soil as well. This results in an above ground mound that can collect warmth from the sun and provide drier conditions and an underground series of galleries that provide cooler, moister conditions. Fire ants use this to their advantage by continually moving brood to the area of the nest that provides the most suitable environment. During cool wet periods this may be the above ground portion of the nest, while during hot dry periods the brood and the majority of the colony members will remain in the deeper underground galleries.

The height and visibility of fire ant mounds varies with weather and temperature. During cool wet periods the workers will build the mound high above the soil, so they can keep the brood warm and dry. During hot dry periods they tend to stay deeper in the soil, so they can keep the brood cool and moist, and even large colonies may not be visible above the grass. This is why fire ants often seem to be more abundant in early spring. Not only are mounds taller at this time, but vegetation is shorter, making mounds more conspicuous.

Where is the door? Normally, there are no external openings in the top of the mound. Foraging ants enter and exit the nest through an array of foraging tunnels that are located slightly below the soil surface and extend in all directions from the mound. These forage tunnels eventually exit to the soil surface several feet away from the nest.

Swarming

An exception to the absence of external openings in the top of the mound occurs when a colony swarms. Swarming is the way fire ant colonies reproduce themselves. Workers break openings through the crust of soil on top of the mound and winged, unmated male and female reproductives exit the mound. These unmated males and females take flight and mate in the air, often several hundred feet above the ground. Swarming occurs from spring through late fall. Swarms are especially common one to two days after a rain event that has been preceded by a dry period.

After they have mated the young queens settle back to the ground, shed their wings, and begin to establish a new colony (Figure 2). They do this by digging a small tunnel a couple of inches into the soil, sealing the opening, and beginning to lay eggs. During this time the queen subsists on nutrients derived from the breakdown of her wing muscles.

Figure 2. The smallest possible fire ant colony! This young fire ant queen has just landed after her mating flight, has shed her wings, and is attempting to start a new colony.

The workers that emerge from the first eggs are unusually small, but they are able to assist the queen in producing more brood, and they also begin foraging for food and expanding the nest. Most young queens attempting to establish new colonies are unsuccessful. They are eaten by a variety of predators, including foraging workers from fire ant colonies, and many simply perish due to inadequate resources. A successful colony can grow to over 100,000 individuals, and begin producing swarms of its own, in six to nine months.

During the mating flight, air currents can carry winged ants considerable distances from their original colony and this is one of the main ways fire ants expand their range. Sometimes man unwittingly helps transport newly mated queens or established colonies of fire ants over long distances. That’s how fire ants got here in the first place. They were brought to the Port of Mobile by boat, probably in soil used as ballast. Accidental transport of fire ants is a possibility any time soil-containing items, such as sod or potted plants, are transported from fire ant infested areas. USDA maintains a quarantine to minimize this potential.

Feeding and Foraging Behavior

Fire ants are omnivorous and feed on a wide variety of plant and animal material. They are active predators and scavengers, eating any live insects they are able to capture as well as dead insects. They also ‘tend’ aphids (Figure 3), scale insects, and other homopterous insects for the honeydew they produce.

Figure 3. Fire ants often tend aphids and other honeydew-producing insects for the sugar-rich honeydew they produce.

Fire ants also prey on small, ground-dwelling vertebrates, including mammals, such as mice, ground-nesting birds, and ground dwelling reptiles and amphibians. In most cases it is the hatching eggs or helpless, immobile young that are attacked. Several studies have shown the abundance of ground-dwelling animals declines significantly when there are high densities of imported fire ants. Fire ants also opportunistically feed on carcasses of larger animals and will attack sick or injured animals that have become immobile. Although fire ants rarely feed on plant foliage, they do feed on plant exudates, and they actively forage for fruit and seed, and occasionally feed on the inner bark of shrubs and trees. Seed are an especially favored food source, because of their high protein and oil content.

It’s the older workers that do the foraging, leaving the colony through tunnels that radiate from the mound. These tunnels usually run just below the soil surface and exit to the surface some distance away from the colony, usually within five to 20 feet. But in hard or gravely soils foraging tunnels sometimes run along the surface. Upon exiting, foraging workers fan out in search of food. When traveling along the surface, workers use chemicals exuded from the tip of their abdomen to lay a chemical trail they can follow back to the mound.

Workers that are successful in locating a large food source recruit other workers by exchanging bits of the food with them and by laying a return trail from the source. As additional workers follow this trail they enhance it with scent of their own, and this recruits even more workers. Thus, a substantial food source can attract a large, steady stream of foraging workers in a relatively short period of time. If you want to see just how fast fire ant workers will recruit to a food source, just lay a greasy potato chip on the ground in a fire ant infested area and check it ten to fifteen minutes later.

Adult fire ants are not capable of eating solid foods they have a sieve-like structure in their throat that prevents them from swallowing solids. Solid food particles are carried back to the colony and fed to the older larvae, which are capable of converting them to liquids. The larvae then regurgitate this liquid food to the tending workers who pass it to other workers, as well to the queen and younger larvae. This process is known as trophalyxis, and it is also common in other social insects, like termites and honeybees. This habit of sharing food among all members of the colony is the main reason baits are such an effective way to control fire ants.


Bipolar drug turns foraging ants into scouts

Whether foraging for food, caring for young, or defending the nest, the worker castes of carpenter ants toil selflessly for their queen and colony. Now, biologists have figured out how to make some of those worker ants labor even harder, or change their very jobs in ant society, all by making small chemical modifications to their DNA.

The finding calls attention to a new source of behavioral flexibility, and drives home the idea that so-called epigenetic modifications can connect genes to the environment, linking nature to nurture. The work is “a pioneering study establishing a causal link between epigenetics and complex social behavior,” says Ehab Abouheif, an evolutionary developmental biologist at McGill University, Montreal, in Canada. “These mechanisms may extend far beyond ants to other organisms with social behavior.”

Insect biologists have long debated whether the division of labor in these sophisticated species with castes is driven by colony needs or is innate. Evidence in honey bees had pointed toward a genetic difference between queens and workers. In the past several years, however, work in both honey bees and ants had indicated that epigenetic modifications—changes to DNA other than to its sequence of bases (or DNA “letters”)—influence caste choices, indicating environmental factors can be pivotal. But subsequent research about one type of change, methylation, led to contradictory conclusions.

Daniel Simola, a computational biologist at the University of Pennsylvania, knew almost nothing about ants when he joined Shelley Berger’s epigenetics lab in Philadelphia, Pennsylvania. But he did want to explore how epigenetics contributes to an organism’s ability to respond to environmental changes, and decided to use one of the ants, Camponotus floridanus, that Berger worked with for such studies. Like other carpenter ants, this species has two worker castes: smaller minors, and bigger majors with larger heads (see photo).

Examples of the minor (left) and major worker castes of Camponotus floridanus.

One essential job for workers is foraging, and Simola and his colleagues quantified how much the two castes did by marking individual ants, letting them go hungry for a day, and recording how often they searched for and retrieved food.

Minors foraged a lot more than majors and were fast at the job, particularly when they were young, Simola found. It’s not clear what majors do, though some have suggested that given their size, they may defend the nest or carry large food items.

He and his colleagues then tested whether epigenetic differences were responsible for this division of labor.

An earlier study by Berger’s group indicated that variations in the number of a chemical entity called an acetyl group on proteins called histones, which serve as the scaffolding for DNA, might be important. Acetylation seems to loosen a histone’s tie on DNA, allowing genes nearby to be more active.

So Simola and his colleagues treated different sets of minors and majors with chemicals that affected the addition or removal of acetyl groups from histones. One, a mood-stabilizing drug for bipolar disorders, inhibits the enzyme histone deacetylase, which removes acetyl groups, damping gene activity. Another inhibits an enzyme that adds acetyl groups. When a treatment resulted in greater histone acetylation in the ants, minors revved up foraging and even started taking on the job of the scout caste, looking in new places for food. Young majors also began to forage regularly and scout, something they typically don’t do, the team reports today online in Science. “We can reprogram the behavior,” Simola concludes.

“It was surprising that they were able to manipulate the foraging behavior through molecular mechanisms so cleanly,” Abouheif says. Changes in older ants of either caste were more subtle, suggesting a window of malleability exists in younger workers.

Moreover, the work shows the power of histone acetylation, in addition to methylation. “DNA methylation has become nearly synonymous with epigenetics,” says Brendan Hunt, an insect geneticist at the University of Georgia in Griffin. “This research brings needed attention to the importance of other epigenetics marks, like histone modifications.”

“We finally have a mechanism to understand ‘nurture’ in molecular terms,” says Gene Robinson, a geneticist at the University of Illinois, Urbana-Champaign, who studies caste determination in honey bees. The ant study, he adds, highlights “how the environment gets under the skin to affect gene expression, and consequently, neural activity and behavior.”


Materials and Methods

Study sites

Preference trials were carried out during austral spring (October 2007), as this is the optimum time for application of baits because ant populations are low ( Nelson and Daane 2007). Foraging activity evaluations were carried out during summer (December 2007, January and February 2008) in the Stellenbosch Winelands region. Ideally this should also have been conducted in spring, but selection of a suitable marker for the ants delayed this experiment. Linepithema humile trials were carried out at Joostenberg farm (33.80S, 18.81E), C. peringueyi at La Motte farm (33.88S, 19.08E), and A. custodiens trials were carried out at Plaisir de Merle farm (33.87S, 18.94E). Drip irrigation was used in all vineyards. The Plaisir de Merle site was a trellised white Chenin blanc vineyard, the La Motte vineyard comprised trellised white Chenin blanc grapes, and the Joostenberg farm had trellised red Pinotage wine grapes. In all vineyards, standard sprays of alpha-cypermethrin and chlorpyrifos were routinely used to control ants during the growing season.

Experiment 1: Determination of ant foraging activity

Trial layout and sampling methods. Five bait stations were placed 10 m apart ( Daane et al. 2006) on one side of the perimeter of a vineyard block approximately 100 m x 100 m, and ants were allowed to feed on 25% sugar solution that had been labeled with 0.25% calco red (N-1700 ® , Passaic Color and Chemical Company, Paterson, New Jersey). These foraging activity trials were carried out on three dates (December 2007, January and February 2008). The calco red labeled sugar water was soaked in cotton wool and held in place on Petri dishes. The concentration of calco red dye used followed recommendations from literature (see discussions in Vega and Rust 2001). Ants were allowed to forage on the calco red labeled sugar water for one week before ant sampling was done. The labeled sugar was replenished once during the week because the bait easily dried out due to crystallization of the sugar component.

Seven days after placing baits into vineyards, thirty pitfall traps were arranged in five transects of 1, 2, 4, 8, 16, and 32 m from the bait stations running along the vine rows. All pitfalls ran along vine rows where the baits were placed. Each bait station had one transect associated with it, replicated five times (over five rows 10 m apart) to give a total of 30 traps. Pitfall traps consisted of plastic containers (35 mm diameter x 60 mm height). These were drilled into the soil, and the soil surface was leveled so that the trap rim was flush with the soil surface. Approximately 4 mL of three parts concentrated glycerol and seven parts 70% ethyl alcohol were placed in each of the pitfall traps to preserve the captured ants (following Majer 1978). This liquid is relatively non-volatile. Pitfall traps were left in the vineyard for 48 hours, after which the traps and their catch were collected for laboratory analysis.

When pitfall traps were being collected, tuna baits were used to sample arboreal ant species, as these would not have been sampled in pitfall traps and are also potential pest species. Crematogaster peringueyi forage and nest in the vine canopy, while the other species mentioned nest primarily on the ground. Roughly 5 cm 3 of shredded tuna chunks were placed in small plastic containers (70 mm diameter x 7 mm height) at the crutch of vines above each of the pitfall traps along each of the five transects. Ants were left to forage on the tuna for 30 minutes, after which all ants feeding on the tuna bait were collected by sweeping them in different containers containing 70% ethyl alcohol as a preservative.

Ant samples collected from both pitfall and tuna traps were taken to the laboratory for analysis. Calco red positive ants were detected by crushing the ant’s abdomen on white paper towels and observing its coloration through a microscope. A pink coloration of the abdomen indicated the presence of calco red.

Experiment 2: Food preference assessments

Eight food attractants (bait matrices) were assessed for their attractiveness to L. humile, C. peringueyi, and A. custodiens during spring (October) 2007. These included: (1) 25% sugar solution (2) agar (in 25% sugar solution) (Warren Chemical Specialities, www.warrenchem.co.za) (3) tuna (Pick’n pay, www.picknpay.co.za) (4) honey (Fleures ® Honey Products, Pretoria, South Africa) (5) dog food (Boss ® chicken beef and beef platter, Promeal Private Limited, South Africa) (6) dry fish meal (7) dry sorghum grit (8) 25% peanut butter (in distilled water) (Nola Yum Yum ® , Nola, Randfontein, South Africa). Tests were conducted in vineyards using choice test arenas. Choice test arenas were made of round plastic containers (270 mm diameter by 65 mm height) with eight plastic tubes (125 mm long by 8 mm diameter) that extended through eight openings at 45° in the inside of the choice test arena, as described in Tollerup et al. (2004). The tubes directed all ants to the center of the choice test arena before they could forage on a bait of their choice. Ants were free to move in and out of the choice test arenas during the test period. Five choice test arenas were used (five replicates), and eight bait matrices, approximately 10 mL, were placed in small Petri dishes, which were randomly assigned to positions in the choice test arenas on the perimeter of the test arena. Active ant nests were selected in the vineyards, and each arena was placed close by, with approximately 10 m distance between arenas. Ants were allowed to forage on the baits, and the experiment was replicated at five nests for each of the three ant species. Each experiment started at

08:00 hours in the morning, after which ant counts occurred hourly for four hours following food deployment. Specifically, this was done by counting the number of ants sitting at each bait matrice at every hour. For L. humile, Rust et al. (2000) reported increased foraging activity in the afternoon compared to mornings, but this may be dependent on microhabitat temperatures, which may differ from in different habitats and has not been tested for L. humile, C. peringueyi, and A. custodienns in a South African context.

Data collection and analysis

The proportion of ants testing positive for calco red for each of the respective distances of the two trapping methods and for each of the three ant species was calculated. For each distance, and for each of the two trapping methods, data were pooled across the five transects. Since the results (proportion of calco red positive ants) were measured under different conditions (months), using standard ANOVA in this case was inappropriate because it fails to model the correlation between the repeated measures. The proportion of ants that carried the dye labeled sugar water at each of the various distances from the bait source for the two trapping methods was therefore calculated for each ant species using repeated measures ANOVA in Statistica 7 (StatSoft, www.statsoft.com). Tukey-Kramer’s post hoc tests were used to identify statistically heterogeneous means. During the food preference tests, the number of ants foraging at each bait station was recorded at hourly intervals up to four hours. Before analysis, data were checked for normality and equality of variances using the Shapiro-Wilk test and Hartley-Bartlett tests, respectively, and in all cases these assumptions were met. Results were then subjected to ANOVA in Statistica 7, and Tukey-Kramer’s post hoc test was again used to separate means.


Controlling Carpenter Ants

It is important to remember that finding carpenter ants foraging inside your home does not necessarily mean that they are nesting indoors. Do not panic and do not resort to spraying insecticides indoors where you see ants. Although spraying stops ant foraging for a while, it only serves to detour them elsewhere (possibly elsewhere indoors) and they will likely return when the chemical residue is gone. More importantly, you may be delaying the inevitable discovery that the ants are actually damaging your home. The first step in controlling carpenter ants is to determine if they are nesting indoors. Spraying your foundation with any of the commonly available insecticides may keep foraging ants away temporarily, giving you a clue as to the source of the ants. (Check the North Carolina Agricultural Chemicals Manual for a list of chemicals that can be use). If ant activity continues at about the same level, then you may very well have an indoor infestation. As an alternative to spraying, you can try baiting the ants outdoors. Put small amounts of honey mixed in water into bottle caps (or similar small containers) and place them along the foundation. Carpenter ants are more active at night, so do your investigation after sunset. Try to follow the ants as they move away from the baits and back to their nest. In most situations the ant nest is located nearby, although it could be as much as 300 feet away from where you find foraging ants. The main purpose of this baiting is simply to see where the ant trail leads. If the ant trails move away from the house, you can use one of the control methods mentioned below for outdoor infestations. If the ants appear to be nesting indoors, the next step is to carefully inspect for likely nesting sites. Concentrate first on those areas around your home that are most vulnerable to moisture problems. Probing the wood with a screwdriver or ice pick is a good way to uncover damage by a number of wood-destroying pests, including carpenter ants and termites. Careful inspection of the attic and crawlspace are important. Because of the time-consuming and tedious nature of a thorough inspection, you may want to enlist the help of a pest control company that has the experience and the ability to quickly find and eliminate the ants.

Indoor infestations - Simply spraying surfaces where you where you see ants foraging is not likely to solve the problem. The ants are likely to move to some other area (still indoors) and may return later when the chemical residue is diminished. Ant baits, particularly those containing hydramethylnon, sulfluramid, avermectin or boric acid, can be effective if the ants are foraging for food. If the ants are gathering around water sources (e.g., a sink), they may not be attracted immediately to the bait. In general, baits are the best approach to dealing with ants. They are more effective in the long term and are less hazardous (compared to sprays) when used properly. However, they may require 7-10 days before ant activity declines significantly. You must be willing to tolerate some ant activity to give the foragers enough time to carry the bait back to the nest where it will be fed to the larvae, other workers and to the queen. Do not spray areas where you will place the bait otherwise, the ants will avoid these areas and not pick up the bait. If ant activity continues at about the same level for several weeks, then you need to take additional steps to deal with the problem. Before spraying, you should first determine the extent of any structural damage caused by the ants. The may require removing siding or portions of sheetrock (indoors). If the damage is severe, repairing and/or replacing wood (and subsequently removing the nest) may be more important than any treatment, and may solve the problem in the process. If damage is minor, then you can use of a pesticide that is labeled for application to wood to eliminate the nest. Effective control often requires the injection of insecticidal dusts or sprays into voids or into the nest. These treatments are complex and may be too difficult for the average person to carry out safely. Contact a pest control professional for help in these situations.

Outdoor treatments - If the ants are foraging from an outdoor nest that cannot be found, then a perimeter treatment can help. Liquid or granular insecticides applied to/along the foundation will cut foraging activity temporarily, but they will not prevent ants from returning at some later date. A list of these products can be found in the North Carolina Agricultural Chemicals Manual. A better choice might be a granular ant bait sprinkled in a 8-12" area on the soil along the foundation. Combat®, which is available in most retail stores, as well as the professional ant baits Maxforce® and Advance® are commonly used for ants, including carpenter ants. Other baits may also be available. Note: Granular baits are not the same as the granular insecticides that are often used for controlling lawn pests. Granular insecticides may be helpful, but must be watered into the soil.
Read the product labels carefully to be sure that you buy the right product.


Biology and habits

Mature carpenter ant colonies produce male and female winged reproductive ants (Fig. 3). Environmental conditions cause reproductive ants to emerge and swarm. They mate during these swarms (nuptial flights), which may occur over several days or weeks. After the nuptial flight, the males die and the females begin searching for a nesting site.

After establishing the nest, the female lays eggs and cares for the larvae by feeding them with fluids secreted from her body. Under favorable conditions, the larvae grow, pupate, and become adult worker ants in 4 to 8 weeks. After becoming adults, the new generations of workers expand the nest, excavate galleries, and take over the task of providing food for the queen and larvae.

Carpenter ant colonies start out small the first 2 or 3 years, but then grow rapidly. In 4 to 6 years they can contain up to 3,000 or more ants, depending on the species. These ants can also have interconnected satellite colonies.

Older, mature colonies continuously produce winged reproductives to replace those that die. They produce 200 to 400 winged individuals for reproductive flights each year. Winged reproductives usually develop in late summer, spend winter in the nest, and swarm in spring and early summer.


RESULTS

Setup: manipulating foraging task access

The setup period aimed to create a negative correlation between recent foraging success and corpulence. During the setup period, over the course of the five foraging sessions the ants leaving the nest were increasingly more likely to be more corpulent (Fig. 2A), meaning that at the end of the period, the ants with the most recent experience of foraging success were more corpulent than those with less recent success. To demonstrate that this significant trend is not part of an intrinsic cycle within the colony, the corpulence of ants attempting to leave the nest (including those on the ‘denied’ list unable to leave) is shown in Fig. 2B. The corpulence of the ants attempting to leave does not change over the course of the foraging period, indicating that it is the manipulation of the exit-controlling doors that causes the change in Fig. 2A. The rate of attempts to leave by individuals on the ‘denied’ list during the setup period was significantly higher than the rate of exits made by the same ant prior to their being placed on the ‘denied’ list (Wilcoxon paired test: V=3073, N=84, P<0.0001). This provides further evidence that the doors were actively preventing attempted exits, because ants that were on the denied list clearly continued to make repeated attempts to leave the nest. This difference was not due to a general increase in activity over this time period, as the rate of trips outside the nest per ant prior to being added to the ‘denied’ list did not increase over the pre-set-up exploration and set-up periods [Page trend test: L=487, m=5 colonies, n=7 days, not significant (NS)], nor did the rate of attempts to leave per ant made by ants on the ‘denied’ list increase over the foraging period (Page trend test: L=207, m=5 colonies, n=5 days, NS).


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