Nest-founding in <Emphasis Type="Italic">Acromyrmex octospinosus</Emphasis> (Hymenoptera,Formicidae, Attini): demography and putative prophylactic behaviors

Summary Foundresses of the leaf-cutting ant Acromyrmex octospinosus in central Panamá forage for leaves as garden substrate (semi-claustral foundation). The fungal pellet and substrate usually are attached to rootlets, which are used as a platform for the garden. This arrangement keeps the garden suspended away from the earthen chamber of the underground nest during early colony growth, and we hypothesize that it serves to minimize contact between the garden and contaminants. A. octospinosus foundresses produce from 3 to 7 workers in 2.7 months after founding the nest, but workers do not forage for substrate at this time. Incipient nests died or were abandoned at a monthly rate of ca. 50%. We show that ants routinely clean their legs before manipulating the garden substrate. We also describe how foundresses use their fore-legs to rub the surface of the metapleural gland (MPG), and they then use typical grooming behaviors to pass the forelegs through the mouthparts, after which the ant then licks the garden substrate. Similarly, ants apparently use their mouths to transfer fecal droplets to their legs. We briefly discuss the functional significance of these grooming behaviors, and hypothesize that they are prophylactic behaviors that may help the foundress maintain a hygienic garden.     

Tuned protection of aphids by ants against a predatory hoverfly

1. Aphid‐tending ants that feed on honeydew have evolved strategies against aphidophagous insects and tune their aggressive behaviour according to the level of danger for their trophobionts. Here we investigate how Lasius niger Linnaeus (Hymenoptera: Formicidae) ants react to different instars of Episyrphus balteatus De Geer (Diptera: Syrphidae) hoverflies which vary in their voracity and defensive abilities. 2. During pairwise encounters, early syrphid instars (eggs, L1, and L2 larvae) elicited lower aggression scores compared to third larval instars (L3), which was intensively bitten by ants. L3 tried to escape from ants by releasing a sticky and toxic secretion over biting ants that died or underwent severe morbidity. 3. In a standardised system including the host plant, aphid, tending ant, and hoverfly, the ability of ants to protect an Aphis fabae Scopoli (Hemiptera: Aphididae) colony was evaluated. Early E. balteatus instars placed onto the plant elicited no mobilisation of ants, which often removed the hoverfly successfully. Eggs and early instars appeared as the weak links for integrated pest management by hoverfly auxiliaries. 4. In contrast, L3 induced the number of ant patrollers to increase at a local scale without any further recruitment from inside the ant nest. L3 syrphids were quite efficient at gluing ants with defensive secretions and at resisting to removal attempts by ants. 5. While supporting the assumption that ants tune their defensive response to the aphidophagous predator, the present results also showed a lack of efficient protection of their trophobionts from the most voracious late syrphid instar.     

Size matters: nest colonization patterns for twig‐nesting ants

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Mothers vigilantly guard nests after partial brood loss: a cue of nest predation risk in a paper wasp

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Ecological barriers to early colony establishment in three coexisting acacia-ant species in Kenya

In black cotton uplands in East Africa, four symbiotic acacia-ant species compete for possession of a single swollen thorn tree species, Acacia drepanolobium, and yet coexist at fine spatial scales. Three of the four ant species produce independent foundress queens that establish colonies claustrally within swollen thorns, most often on small saplings. We conducted surveys of such saplings at two sites in 2001 and 2004, and examined foundresses and incipient colonies within their swollen thorns to determine what factors influence their success. Competition among foundresses for nest initiation sites was intense, with an average of over one founding attempt per swollen thorn in all samples, and with living and dead queens significantly hyper-dispersed among available thorns. Combat with other foundresses was the most common cause of death among claustral queens, especially for Tetraponera penzigi. In interspecific battles for nest initiation sites, T. penzigi was dominant over Crematogaster nigriceps and C. mimosae, and C. nigriceps won over 80% of its contests with C. mimosae foundresses. For singleton foundresses, brood parasitism by the braconid wasp Trigastrotheca laikipiensis typically results in the death of the entire ant brood. Host queens defend parasite larvae, pupae and eclosed adults, apparently unable to distinguish the wasps from legitimate offspring. Rates of brood parasitism were as high as 15–20% for incipient colonies of both Crematogaster species, but were extremely low for T. nigriceps in all samples. Although T. penzigi and C. nigriceps foundresses are always solitary, approximately 18% of claustral C. mimosae colonies contain cooperating pleometrotic queens. For unparasitized, claustral C. mimosae colonies, brood production per queen did not differ between solitary and cooperating foundresses. However, the per-capita risks associated with parastitism were reduced for pleometrotic queens. Received 8 March 2005; revised 23 May 2005; accepted 3 June 2005.     

Process of comb division of reused nests in the Australian paper waspRopalidia plebeiana (Hymenoptera,Vespidae)

Summary InRopalidia plebeiana, combs made in the previous year are often reused by foundresses in the following spring and structurally divided into subnests by them. Close observations of the comb dividing process revealed that: 1) combs that had multiple brood areas (areas where cells had eggs) were frequently divided into subnests, while those with single brood areas were never divided; 2) groups of foundresses each occupied a particular brood area even before comb division started; and 3) frequency with which a foundress practiced comb cutting was independent of her social status or oviposition frequency. These observations suggest that the initial grouping of foundresses that colonize an old nest leads to subsequent comb division, rather than the major egg layers cutting combs to safeguard their oviposition territories from their rivals.     

Costs and benefits of joint colony founding in Australian Acacia thrips

Facultative joint colony founding by social insects (pleometrosis) provides an outstanding opportunity to analyze the costs and benefits of sociality. Pleometrosis has been documented for a range of social insects, but most studies on the adaptive benefits of this behavior are restricted to the Hymenoptera. In this study, we provide the first analysis of costs and benefits associated with pleometrosis for Australian Dunatothrips, which form domiciles by glueing together phyllodes (leaves) of their Acacia host plant. In Dunatothrips aneurae, the distribution of foundress numbers per nest indicated that females formed associations non-randomly. Furthermore, average group size was independent of both the number of foundresses on the host plant and the number of mature colonies, suggesting that this behavior was not simply a response to limited availability of nesting sites. Although per capita reproduction declined with increasing group size, we also identified two benefits of pleometrosis: (1) individual foundresses in groups had higher survival than solitary foundresses during the brood development period, and (2) larger colony sizes resulting from pleometrosis provided a benefit later in colony development, because a higher proportion of D. aneurae adults survived invasions by the kleptoparasite Xaniothrips mulga when colony size was larger. These results demonstrate that the reproductive costs of pleometrosis are at least partially counterbalanced by survival benefits. Received 4 April 2006; revised 9 September 2006; accepted 20 September 2006.     

Why Wasp Foundresses Change Nests: Relatedness,Dominance, and Nest Quality

The costs and benefits of different social options are best understood when individuals can be followed as they make different choices, something that can be difficult in social insects. In this detailed study, we follow overwintered females of the social wasp Polistes carolina through different nesting strategies in a stratified habitat where nest site quality varies with proximity to a foraging area, and genetic relatedness among females is known. Females may initiate nests, join nests temporarily or permanently, or abandon nests. Females can become helpers or egglayers, effectively workers or queens. What they actually do can be predicted by a combination of ecological and relatedness factors. Advantages through increased lifetime success of individuals and nests drives foundresses of the social wasp Polistes from solitary to social nest founding. We studied reproductive options of spring foundresses of P. carolina by monitoring individually-marked wasps and assessing reproductive success of each foundress by using DNA microsatellites. We examined what behavioral decisions foundresses make after relaxing a strong ecological constraint, shortage of nesting sites. We also look at the reproductive consequences of different behaviors. As in other Polistes, the most successful strategy for a foundress was to initiate a nest as early as possible and then accept others as subordinates. A common feature for many P. carolina foundresses was, however, that they reassessed their reproductive options by actively monitoring other nests at the field site and sometimes moving permanently to new nests should that offer better (inclusive) fitness prospects compared to their original nests. A clear motivation for moving to new nests was high genetic relatedness; by the end of the foundress period all females were on nests with full sisters.     

Two new myrmecophytic associations from the Malay Peninsula: Ants of the genusCladomyrma (Formicidae,Camponotinae) as partners ofSaraca thaipingensis (Caesalpiniaceae) andCrypteronia griffithii (Crypteroniaceae)

Summary In Peninsular Malaysia the treesSaraca thaipingensis (Caesalpiniaceae) andCrypteronia griffithii (Crypteroniaceae) are inhabited by ants. In the vicinity of Gombak, near Kuala Lumpur, the hollow internodes of youngSaraca thaipingensis plants are colonized mainly by twoCladomyrma species. In larger trees aCrematogaster sp. is also found.Crypteronia griffithii is inhabited by a third species ofCladomyrma. None of these species is conspecific with any of the threeCladomyrma taxa so far described. The colonies are founded by single mated queens, which have a conspicuous, sphecid wasp-like behaviour when searching for host plants and nest sites. They chew holes into the plant internodes and hollow them out to provide nest sites. Coccids and pseudococcids are cultivated within the internodes. The homopterans are not carried by queens on their nuptial flights. They apparently find their way by themselves into the cavities or are perhaps carried there by the worker ants. TheCladomyrma ants onCrypteronia are not aggressive, in contrast to those onSaraca thaipingensis.The relationship ofCrypteronia with ants seems to be obligatory, whereasSaraca was only partly colonized byCladomyrma. The interaction ofSaraca withCrematogaster sp. is loose and facultative, since theCrematogaster sp. also lives on other three species. Our studies have now revealed fourCladomyrma spp. which are regularly associated with plants. The genus therefore seems to have an entirely myrmecophytic way of life.     

Demography of the Okinawan eusocial wasp Ropalidia fasciata (Hymenoptera: Vespidae) I. Survival rate of individuals and colonies, and yearly fluctuations in colony density

We conducted a series of demographic studies of the primitively eusocial wasp Ropalidia fasciata in Okinawa, a subtropical part of Japan, and found the following. The colony cycle of this wasp is annual, spanning from April to November or even December; this is longer than the colony cycles of other temperate polistine wasps so far reported. The survival rate of the marked foundresses was 40% to June, dropping to 1.4% by September. These survival rates are similar to other subtropical and tropical species. Most females that emerged in November were probably second generation adults (progeny of the original foundresses), which would participate in founding nests in the following spring. These facts indicate that R. fasciata in Okinawa is at least partially bivoltine. Survival of a nest to September was 10–20%; however, because a failed nest is often rebuilt, survival of the colony to September was as high as 50%. The mean number of new foundresses produced per foundress was 7.5, and their overwintering survival was 16%. Hence, a single foundress produced, on average, 1.2 progeny foundresses to the following year. Density dependence was shown in the rate at which the progeny foundresses were produced. These results explain the remarkable stability of nest densities from year to year in the area. The above results reveal that R. fasciata in Okinawa shares many demographic characteristics with other primitively eusocial wasps, particularly year‐to‐year stability of nest density and a long colony cycle.     

Colony development and social structure in a subtropical paper wasp,Ropalidia fasciata (F.) (Hymenoptera: Vespidae)

More than 50% of nests of Ropalidia fasciata were founded by association of foundresses (multifemale nests). The multifemale nests were generally initiated earlier and grew faster than the single-female nests. The survival rate of the multifemale nests was significantly higher than that of single-female nests, and the productivity as measured by the number of cells produced per foundress had a peak at a foundress-group size from 6 to 10. The number of marked foundresses which were seen on their original nest decreased as the colony cycle proceeded, but some of them continued to coexist on the original nests after emergency of many female progeny. Except in the case where a large number of foundresses attended a young nest so that some foundresses could not sit on the nest, the dominance interactions among cofoundresses were mild. More than twothirds (71.4%) of nests (including those at the post-emergence stage) had multiple egg-layers. The foundress association in this species is considered to be beneficial for every foundress because it raises ability to avoid predation or to reconstruct their nests when the nests are destroyed by typhoons.     

Honey supplementation and its developmental consequences: evidence for food limitation in a paper wasp, Polistes metricus

ABSTRACT.

• 1 Polistes metricus Say (Hymenoptera: Vespidae, Polistinae) field colonies were supplemented with dilute honey during the pre-emergence and early post-emergence phases of colony development.
• 2 Supplementation did not increase number of nest cells constructed or rates of loss to predation or foundress disappearance compared with controls.
• 3 Colonies receiving honey supplementation produced first offspring earlier in the season than control colonies. The difference is due to a shorter time span between founding and first emergence.
• 4 Foundresses of supplemented and control colonies did not differ in wing length or per cent body fat.
• 5 Offspring of both supplemented and control colonies had shorter wing lengths than did foundresses of supplemented colonies. Offspring of control colonies had shorter wing lengths than did foundresses of control colonies but not foundresses of supplemented colonies.
• 6 The per cent body fat of offspring from control colonies was lower than that of all foundresses and of offspring from supplemented colonies.
• 7 The per cent body fat of offspring from supplemented colonies was higher than that of all foundresses.

     

Nest raiding by the invasive Argentine ant on colonies of the harvester ant, Pogonomyrmex subnitidus

Invasive ants often displace native ants, and published studies that focus on these interactions usually emphasize interspecific competition for food resources as a key mechanism responsible for the demise of native ants. Although less well documented, nest raiding by invasive ants may also contribute to the extirpation of native ants. In coastal southern California, for example, invasive Argentine ants (Linepithema humile) commonly raid colonies of the harvester ant, Pogonomyrmex subnitidus. On a seasonal basis the frequency and intensity of raids vary, but raids occur only when abiotic conditions are suitable for both species. In the short term these organized attacks cause harvester ants to cease foraging and to plug their nest entrances. In unstaged, one-on-one interactions between P. subnitidus and L. humile workers, Argentine ants behaved aggressively in over two thirds of all pair-wise interactions, despite the much larger size of P. subnitidus. The short-term introduction of experimental Argentine ant colonies outside of P. subnitidus nest entrances stimulated behaviors similar to those observed in raids: P. subnitidus decreased its foraging activity and increased the number of nest entrance workers (many of which labored to plug their nest entrances). Raids are not likely to be the result of competition for food. As expected, P. subnitidus foraged primarily on plant material (85% of food items obtained from returning foragers), but also collected some dead insects (7% of food items). In buffet-style choice tests in which we offered Argentine ants food items obtained from P. subnitidus, L. humile only showed interest in dead insects. In other feeding trials L. humile consistently moved harvester ant brood into their nests (where they were presumably consumed) but showed little interest in freshly dead workers. The raiding behavior described here obscures the distinction between interspecific competition and predation, and may well play an important role in the displacement of native ants, especially those that are ecologically dissimilar to L. humile with respect to diet. Received 15 July 2005; revised 19 October 2005; accepted 26 October 2005.     

Social behaviour ofRopalidia fasciata (Hymenoptera: Vespidae) females on satellite nests and on a nest with multiple combs

The social behaviour ofRopalidia fasciata females on 3 satellite nests and on a nest with multiple, independent combs was observed. Many females often visited satellite nests, and even dominant foundresses, who usually spent more of their time on the nest, became active when satellite nests were being constructed. Three foundresses laid eggs on a satellite nest and eggs laid by 2 of these (who performed foraging) survived. On another satellite nest, only the dominant foundress laid an egg which survived. On a nest consisting of 2 independent combs, females frequently shifted between the 2 combs even after the emergence of many adults. Constructions of satellite nests and of multiple independent combs are considered to be adaptive for this species living in Okinawa, where most of nests are destroyed by frequent typhoons or abandoned after predation by ants.     

Digging beneath the surface: incipient nest characteristics across three species of harvester ant that differ in colony founding strategy

Ants exhibit a size-associated colony founding trait that is characterized by the degree to which foundresses rely on internal reserves to raise their first brood of workers (claustrality). The reliance on stored reserves is positively correlated with degree of claustrality (claustral > facultative > semi-claustral) and is variable across species of Pogonomyrmex harvester ants. Three species of harvester ant foundresses that differ in degree of claustrality were observed initiating nests under laboratory conditions over 2 years. P. rugosus is fully claustral, P. salinus is facultative, and P. californicus is semi-claustral. Across species, degree of claustrality was positively associated with mean digging rate and nest depth over the first 3 days of nest initiation, total nest depth, and degree of nest closure. Branching and abundance of peripheral nodes were higher in semi-claustral and facultative nests than in claustral nests. The facultative species dug for the longest time and achieved the greatest tunnel length. Within each species, there were trends associating mass with digging rate, but these were not consistent in all species. There were no intraspecific trends of mass with nest depth. Also within species, a foundress’s mass did not affect her tendency to open or close her nest. These results reveal degree of claustrality is correlated across species with several nest initiation characteristics that together may represent different colony founding syndromes.     

Density-dependent ant attendance and its effects on the parasitism of a honeydew-producing scale insect,Ceroplastes rubens

The intensity of attendance by a honeydew-foraging ant, Lasuis niger, on the red wax scale insect, Ceroplastes rubens, was estimated at different manipulated densities in the field. The time that individual ants were present and the total attendance time (seconds x number of ants) of ants on scale-infested twigs significantly increased as the density of C. rubens increased, i.e. ant attendance was density dependent. To determine the effects of density dependence of ant attendance on parasitism of C. rubens by Anicetus beneficus, we measured parasitism rates in the field at different density levels of C. rubens both with ant attendance and with ants excluded. Parasitism rates were higher when ants were excluded, at each density level. Although the parasitism rate significantly deceased as scale density increased, whether or not ants attended, the difference in parasitism rate between density levels was strikingly less without ant attendance. Therefore, the density-dependent decrease of parasitism rate was more pronounced with ant attendance. Mortality not due to parasitism showed density dependence in both conditions and did not change when ants were excluded. These results indicate that attending ants reduce parasitism and that, as a consequence of the density dependence of ant attendance, the efficiency of reduction of parasitism by ants is enhanced at higher densities of C. rubens.     

Stable isotope investigation of a cryptic ant-plant association: Myrmelachista flavocotea (Hymenoptera, Formicidae) and Ocotea spp. (Lauraceae)

An obligate symbiosis between Ocotea dendrodaphne Mez and O. atirrensis Mez & Donn.Sm. (Lauraceae) and their cryptic ant symbiont, Myrmelachista flavocotea, is common in lowland wet forests of Costa Rica, yet it is unclear whether the association is typically mutualistic or parasitic. Ants impose costs by tending trophobionts inside the plant body and further compromise the structural integrity of their host by hollowing its stems. Benefits to the host, including anti-herbivore defense and nutrient provisioning, must outweigh these costs for the association to be mutualistic, but benefits in this system are largely unknown. We adopted a stable isotope approach to investigate trophic relationships among Ocotea hosts, coccoid trophobionts, and worker and larval ants in the understory of mature forest at La Selva Biological Station, Costa Rica. In addition, a natural stable isotope marker (tuna) was made available to M. flavocotea colonies to determine whether ants are fortuitous scavengers and/or provision their host. In this system, we found unusual patterns of isotopic fractionation. For coccoids, nitrogen isotopes are only slightly enriched, and carbon isotopes were depleted relative to the host signature. Moreover, nitrogen signatures of the timid Myrmelachista ants are high, suggesting a substantial degree of carnivory and/or scavenging in this species. In the provisioning study, ant colonies provided with baits demonstrated a significant shift in carbon isotopic composition relative to untreated colonies indicating uptake and assimilation of the bait. These results suggest that these timid ants are patrolling the plant for food and concentrating nutrients in Ocotea’s hollowed stems. Further studies are required to confirm if M. flavocotea provides a net benefit to its host by providing nutrients, reducing herbivory, or by removing detrimental debris from the plants surface.     

Hypoxic conditions and oxygen supply in nests of the mangrove ant, Camponotus anderseni, during and after inundation

The small ant Camponotus anderseni lives exclusively in twigs of the mangrove tree Sonneratia alba, and during inundation, the entrance hole is blocked with a soldier’s head which effectively prevents flooding. The nests can be very crowded, with the ants and coccids filling up to 50% of the volume, and due to their metabolic activity, the conditions in the nests during inundation become hypercapnic and hypoxic. Each nest has only one entrance, and the opening is quite small (1.56 ± 0.03 mm). The mean diameter of the galleries is 2.31 ± 0.23 mm, independent of the thickness of the twig and length of the nest. During normal conditions with open nests, the oxygen depletion is substantial in the part of the nest most distant from the opening, and in a 120 mm long nest the oxygen concentration can be as low as 15.7%. During simulated inundation, in which the nest entrances were blocked, the oxygen concentration dropped to very low levels (<0.5%) after one hour. After opening the nest entrance, the oxygen concentration increased again, but for a 100 mm long nest it took nearly 20 minutes before the concentration was back to the normal depressed level. Mathematical modelling of the steady-state oxygen concentrations in the innermost part of the nests shows a lower O₂ concentration than calculated. The time for equilibration of oxygen after inundation is longer than expected for small nests, presumably because the passive diffusion is obstructed by the nest contents. The “dilemma” faced by C. anderseni is to avoid drowning without suffering anoxia or hypercapnia, and they show a remarkable ability to adapt to the extreme conditions in the mangrove and exploit a niche where the density of other ants is insignificant. Received 13 December 2007; revised 30 July 2008; accepted 6 September 2008.     

The ant’s estimation of distance travelled: experiments with desert ants,<Emphasis Type="Italic"> Cataglyphis fortis</Emphasis>

Foraging desert ants, Cataglyphis fortis, monitor their position relative to the nest by path integration. They continually update the direction and distance to the nest by employing a celestial compass and an odometer. In the present account we addressed the question of how the precision of the ants estimate of its homing distance depends on the distance travelled. We trained ants to forage at different distances in linear channels comprising a nest entrance and a feeder. For testing we caught ants at the feeder and released them in a parallel channel. The results show that ants tend to underestimate their distances travelled. This underestimation is the more pronounced, the larger the foraging distance gets. The quantitative relationship between training distance and the ants estimate of this distance can be described by a logarithmic and an exponential model. The ants odometric undershooting could be adaptive during natural foraging trips insofar as it leads the homing ant to concentrate the major part of its nest-search behaviour on the base of its individual foraging sector, i.e. on its familiar landmark corridor.     

Rubbing behavior and morphology of van der Vecht's gland inBelonogaster petiolata (Hymenoptera: Vespidae)

Females of the social wasp, Belonogaster petiolata,rub the secretion of van der Vecht's gland, located on their terminal gastral sternite, onto the nest pedicel. In bioassays, the secretion was repellent to two species of ants, while shortchain acids were effective releasers of rubbing behavior. Rubbing was associated with pedicel enlargement and departure from the nest in preemergence colonies. Its frequency was high where wasps were often exposed to ants and low where ants were rare or absent. Rubbing also decreased significantly from the pre-to the postemergence stage of the colony cycle. In both stages, subordinate foundresses rubbed more often than queens or workers. These observations support the hypothesis that rubbing behavior and the secretion of van der Vecht's gland function in chemical defense of the nest against ant predation. The general morphology of the gland in B. petiolataresembles that of the four other independent-founding polistine wasp genera.