The basicoxal gland, a new exocrine structure in poneromorph ants (Hymenoptera, Formicidae)

The tegumental epithelium of the outer dorsolateral region in the proximal part of the coxae in the mid‐ and hindlegs of both workers and queens of the ants Odontomachus rixosus and O. simillimus is differentiated into a conspicuous and hitherto unknown exocrine gland. The glandular cells display a clear microvillar differentiation of their apical cell membrane, and are lined with the tegumental cuticle, which in this part contains crack‐like channels perpendicular to its surface, that carry the glandular secretions to the outside. Apical microvilli support the transport of substances, and contain an extension of tubular smooth endoplasmic reticulum in their centre. The function of the gland may be that of providing lubricant substances to the articulation region of the generally heavily sclerotized ponerine ant species. The gland is also found in several other ponerine and amblyoponine species, but not in the ectatommine species studied. The foreleg coxae lack a basicoxal gland in all species examined, which may be explained by the more limited articulation between the thorax and the coxae in the forelegs compared to the mid‐ and hindlegs.     

Raiding behavior of the dulotic antChalepoxenus muellerianus (Finzi) in the field (Hymenoptera: Formicidae,Myrmicinae)

Summary Little information is available regarding the raiding behavior in nature of dulotic ants belonging to the tribeLeptothoracini. Between July 17 and 24, 1991, several raids ofChalepoxenus muellerianus (Finzi) were observed in nature near Tignale/Lago di Garda, Italy. Apparently, this species raids frequently during its summer raiding season (5 raids were observed during 7 days spent observing 8 colonies). A singleChalepoxenus colony sometimes raids more than one host colony more or less simultaneously. Observations during which oneChalepoxenus colony raided another and captured slavemaker brood indicate that intraspecific raids can occur either accidentally, or as a result of competition or territoriality when there is a sufficient dense slavemaker population.     

Arboreal search in ants: Search on branches (Hymenoptera: Formicidae)

Ants (Formicidae) perform two distinct search behaviors for resources: on the ground they use irregular, almost random alternating looping, and on branches and leaves they resort to outline-tracing (arboreal systematic search), whereby the individual systematically turns to one side at bifurcations and to the opposite side when turning about at end points. Experiments with searching Formica pallidefulva and Crematogaster cerasion artificial stick mazes under seminatural conditions demonstrated that bifurcations and end points only trigger turn decisions, whereas an intrinsic mechanism specifies the handedness of such turns. Arboreal homing differs from arboreal searching by a much stronger tendency to rectify paths by counterturning. The theory is advanced that searching on branches by outline-tracing is evolutionarily derived from ranging search by superposing a sustained intrinsic turn bias and by suppressing random turns.     

Unexpected,well-developed nestmate recognition in laboratory colonies of polygyne imported fire ants (Hymenoptera: Formicidae)

Aggression bioassays were used to investigate nestmate recognition in polygyne laboratory colonies of the imported fire ant, Solenopsis invictaBuren. Unlike workers from polygyne field colonies, laboratory-maintained (>10 weeks) workers exhibited well-developed nestmate recognition. As in monogyne colonies of this species, both heritable and environmentally acquired (diet) odors provided recognition cues and were roughly additive in their effect. Within diet treatments, polygyne colonies responded in a graded fashion to polygyne conspecifics, monogyne conspecifics, and heterospecifics (S. richteri Forel),thus suggesting incipient genetic divergence between the two S. invictasocial forms. Hypotheses to account for the acute intraspecific discrimination observed in the laboratory are presented. Empirical testing of these hypotheses will illuminate ecological constraints and proximate mechanisms underlying the reduced intercolony discrimination associated with natural polygyne colonies of this and other ant species.     

Marking of Nest Entrances and Vicinity in Two Related Tetramorium Ant Species (Hymenoptera: Formicidae)

Workers of the related ants Tetramorium impurum and T. caespitum mark the vicinity of their nest entrances in a species-specific manner, as seen by similarities between the behavior of nestmates and that of alien conspecifics (e.g., concerning aggregation, locomotion, orientation, tendency to move, and agonistic behavior). Additionally, they mark the inside of their nest entrances in a colony-specific manner, as seen by the following differences in behavior. Nestmates aggregate on these areas, walk rather slowly, but freely and essentially in the middle of the areas, come toward and very near such areas, are not inclined to escape, and are ready to attack possible intruders. Alien conspecifics do not aggregate, walk quickly, and are reluctant to stay on the areas, come neither toward nor very near the areas, are inclined to escape, and often open their mandibles, mainly when in front of a resident. The marking of the nest entrances is performed by T. impurum in 30 min and by T. caespitum in 15 min. If not reinforced, the marking by both species vanishes in 60 and 50 min, respectively. Extracts of hindlegs, metathorax, or metapleural glands produce in unmarked areas the ethological effect of marked entrances. It may be hypothesized that the marking factor is produced by the workers' metapleural glands and deposited onto the ground, via the hindlegs of ants leaving the nest. A worker's head has a species- but not a colony-specific ethological effect. An isolated alien conspecific's head is never attacked, whereas a thorax with abdomen is. This explains why, by opening its mandibles (and then presumably emitting a mandibular gland pheromone), a conspecific ant momentarily inhibits the attack of a nonnestmate. According to Hölldobler and Wilson (1990), the marking of the inside of T. impurum and T. caespitum nest entrances is a territorial and nest-entrance marking, whereas the marking of the close vicinity of the entrances is a home-range marking, as is the marking of the foraging area. These markings are in accordance with the fact that T. impurum foragers deposit their trail pheromone as far as the opening of the nest entrance.     

Respiratory physiology and water relations of three species of Pogonomyrmex harvester ants (Hymenoptera: Formicidae)

The respiratory physiology and water relations of three harvester ant species (Pogonomyrmex rugosus Emery, P. occidentalis[Cresson] and P. californicus[Buckley]) were examined at three temperatures (15, 25 and 35°C) using a flow-through respirometry system. As intact ants tended to be active during testing, we performed a parallel set of experiments on individuals rendered motionless by decapitation. Both intact and decapitated ants exhibited discontinuous ventilation. Decapitation caused metabolic rate (V˙CO₂) and burst frequency to decrease in all three species. Burst volume either remained constant or increased after removal of the head, though mass-specific V˙CO₂ was unaffected except in P. rugosus. Mass-specific V˙CO₂s of headless harvesters were comparable with published values derived from motionless specimens of other ant species. The mean Q₁₀ for intact ants of all three species was 2.37; for decapitated insects the mean was 2.32. Respiratory water constituted a small (< 5%) fraction of total loss, and we believe that discontinuous ventilation does not act to conserve water in these organisms, although it may serve other functions.     

Characterization of 24 microsatellite markers in 11 species of fire ants in the genus Solenopsis (Hymenoptera: Formicidae)

The social parasite ant Solenopsis daguerrei infests colonies of several mound-building fire ant species. Twenty-four microsatellite markers were isolated from a repeat-enriched genomic library of S. daguerrei. Eleven loci were polymorphic in this ant with two to six alleles per locus. Expected heterozygosity ranged from 0.0222 to 0.7940 among loci. Most microsatellites amplified successfully across the 11 Solenopsis species tested and will be useful for evolutionary genetic studies in this diverse ant group.     

Increase in levels of microbiota recoverable from male and larval Myrmecia gulosa (Fabricius) (Hymenoptera: Formicidae) following segregation from worker ants

The segregation of laboratory maintained male and larval Myrmecia gulosa from workers resulted in increased levels of culturable microbiota. After 29 days, microbial levels recovered from segregated males and larvae were 27 and 126 times greater than from males and larvae not segregated from workers. These findings are consistent with the hypothesis that metapleural gland secretions, absent in larvae and males, are transferred from workers to larvae, and males contribute to the inhibition of cuticular microbiota.     

Acromyrmex ameliae sp. n. （Hymenoptera： Formicidae）： A new social parasite of leaf-cutting ants in Brazil

The fungus-growing ants （Tribe Attini） are a New World group of〉 200 species, all obligate symbionts with a fungus they use for food. Four attine taxa are known to be social parasites of other attines. Acromyrmex （ Pseudoatta） argentina argentina and Acromyrmex （Pseudoatta） argentina platensis （parasites of Acromyrmex lundi）, and Acromyrmex sp. （a parasite of Acromyrmex rugosus） produce no worker caste. In contrast, the recently discovered Acromyrmex insinuator （a parasite of Acromyrmex echinatior） does produce workers. Here, we describe a new species, Acromyrmex ameliae, a social parasite of Acromyrmex subterraneus subterraneus and Acromyrmex subterraneus brunneus in Minas Gerais, Brasil. Like A. insinuator, it produces workers and appears to be closely related to its hosts. Similar social parasites may be fairly common in the fungus-growing ants, but overlooked due to the close resemblance between parasite and host workers.     

Nest-area marking with faeces: a chemical signature that allows colony-level recognition in seed harvesting ants (Hymenoptera, Formicidae)

Summary. Nestmate recognition systems in ants are largely based on chemical signals. The hydrocarbon fraction of the lipid layer which covers the insect cuticle plays a determinant role in this context. Here we report a novel extension of nestmate and alien recognition – nest area marking with faeces containing the same hydrocarbons as the cuticle of workers – in a harvesting ant, Messor capitatus. Workers of M. capitatus deposit large quantities of brown-yellow material from the hindgut (termed spots) in the vicinity of the nest. Behavioural investigation showed that such spotting behaviour has a communicative value in the context of nest area identification. Anal fluids deposited in the nest surroundings contain colony-specific cues which the ants use to recognize their own nest areas, and distinguish them from foreign areas even in the absence of nestmate or alien ants. Chemical analyses by gas chromatography-mass spectrometry (GC-MS) of the contents of anal spots, rectal sacs, and cuticular extracts revealed that all contain the same long-chained linear and branched hydrocarbons in varying proportions. Importantly, multivariate analyses showed that the relative proportions of these compounds on the cuticle and in spots are colony-specific. This provides a mechanism by which spot marking could be used by workers to define and recognize their colony area, and would represent a simple extension of the existing nestmate recognition template based on colonial cuticular signatures. The ecological and sociobiological implications of these findings are discussed.Received 3 February 2004; revised 10 June 2004; accepted 14 June 2004.     

Influence of physical and chemical factors during foraging and culture of the symbiont fungus in Atta sexdens rubropilosa （Hymenoptera： Formicidae）

The aim of this paper is to investigate the influence of physical and chemical factors on transport and use of substrate for Atta sexdens rubropilosa workers. Three types of rectangular fragments were used to study the physical influence factors： filter paper with paraffin, filter paper without paraffin and polyester film. To study the chemical factors, some fragments were impregnated with organic extract of orange albedo, others were soaked with soybean oil and for the remaining ones nothing was applied. The fonowing parameters were evaluated： （i） attractiveness of substrate for transport and number of loading workers per treatment; （ii） foraged material incorporation; （iii） rejection by numbers of fragments deposited in the garbage or beside the fungus garden. All the polyester film fragments carried out to the fungus garden were subsequently rejected. We verified that chemical factors of the substrate were more quickly detected by the workers, whereas physical factors were used as a criterion in the decision-making to reject or accept the substrate collected.     

Digestive enzymes of leaf-cutting ants, Acromyrmex subterraneus (Hymenoptera: Formicidae: Attini): distribution in the gut of adult workers and partial characterization

Enzyme activities associated with the labial glands, midgut and rectum of adult Acromyrmex subterraneus were investigated in order to understand their role in digestion of plant and fungal material. High chitinolytic activity was detected in the labial glands, indicating a possible role in the degradation of fungus ingested by the ants. Chitinolytic activity seen in other compartments of the alimentary canal probably originated in the labial glands. The highest activity detected in the midgut was for alpha-glucosidase, which was considered to be of insect origin due to its association with midgut epithelium and it is probably involved in glucose assimilation from nutrient sources such as maltose and sucrose present in plant material. A large range of enzyme activities were detected in the rectal lumen contents, and as in the midgut the highest values were for alpha-glucosidase activity. The absence of activity associated with the epithelium, in the particulate fraction, indicates that the rectal epithelium does not have a secretory function. The detection of enzymes in the rectal lumen contents, which were not detected in the midgut lumen contents, indicates that the rectum acts as a reservoir, accumulating enzymes. The major digestive enzymes were partially characterized using hydrophobic interaction chromatography, gel filtration and SDS-PAGE. The pH of the adult intestinal tract and flow rate of dye through the tract was investigated. A gradual acidification of the intestinal tract was noted commencing with the crop (pH 6-8.2) and terminating with the rectum (pH 3-5). The flow of dye through the different compartments of the tract showed a rapid fill time for all the gut compartments and a short residence time in the crop. In all other compartments, the dye remained detectable for 10 days or longer.     

Nest composition and worker relatedness in three slave-making ants of the genus Rossomyrmex Arnoldi and their Proformica Ruzsky hosts (Hymenoptera,Formicidae)

Abstract In this paper, we analyze and compare nest composition and architecture as well as worker relatedness in three related species of slave-making ants: Rossomyrmex anatolicus, R. minuchae, and R. quandratinodum. Colony structure within nests is an important trait in ants, especially in the case of mixed societies, when host and parasite coexist in the same nest. Data for their respective free-living hosts, Proformica korbi, P. longiseta and P. sp., are also provided. For our study, we integrated a meticulous excavation procedure with a genetic method. We conclude that the average number of parasites, as well as of slaves, is species-specific, whereas nest depth depends on the nest architecture of the host. The genus Rossomyrmex seems to be monogynous and monandrous, whereas Proformica shows differences in the number of queens and mating frequency. R. quandratinodum shows different traits in nest composition (host/parasite ratio: P/R) and architecture. The difference in traits may account for some differences in parasitism: raid process or avoidance of parasitism.     

Male induction and function of workers' excitability during swarming in leaf-cutting ants (Atta and Acromyrmex) (Hymenoptera,Formicidae)

Worker excitation in species of Atta and Acromyrmex prior to and during the swarming of reproductives is initiated by secretions from the male mandibular glands. During this phase, workers are highly aggressive, attacking all foreign objects. Field data suggest that this behavior is not only advantageous in protecting sexuals as they swarm, but also to prime workers to execute queens trying to initiate colonies near mature colonies following nuptial flights.     

Doronomyrmex pocahontas: not a workerless parasite but still an enigmatic taxon (Hymenoptera,Formicidae)

Summary New data suggest that the North American antDoronomyrmex pocahontas Buschinger 1979, originally described as a workerless inquiline, is not a social parasite. Breeding experiments show a remarkable phenotypic plasticity, which is probably due to hybridization or to intraspecific polymorphism.     

Digestive enzymes in larvae of the leaf cutting ant, Acromyrmex subterraneus (Hymenoptera: Formicidae: Attini)

The digestive physiology and biochemistry of larvae of the leaf-cutting ant Acromyrmex subterraneus were investigated here. The activity of digestive enzymes was evaluated in the labial glands, midgut epithelium (soluble and particulate fractions), and in the lumen contents, separated into endo and ectoperitrophic regions. Enzymes with high levels of activity were partially characterised using chromatography and electrophoresis techniques. Microscope observations were carried out and the anatomy of the larval digestive tract was described here for the first time. Larvae fed with pH indicator solutions showed the anterior portion of the midgut to be acidic and the posterior portion neutral to alkaline, indicating that the pH of the different regions of the midgut could optimise certain enzyme activities, whilst inhibiting others. The flow rate of the intestinal contents was also evaluated in larvae fed with a dye solution. The slow flow rate is probably due to closure of the rear end of the larval midgut. No compartmentalisation of digestive enzymes acting on oligosaccharides and disaccharides in the ectoperitrophic space and on polysaccharides in the endoperitrophic space was observed here, which could also be related to the closure of the midgut. The digestive physiology of these larvae is therefore similar to ancestral Holometabola, a paradox when considering the highly evolved nature of these insects. The larval midgut demonstrated a large diversity of enzyme activities with high levels of alpha-amylase, alpha-mannosidase, chitinase, alpha-glucosidase, beta-glucosidase and proteinase. High levels of chitinase and amylase activities were detected in the labial glands of larvae. The enzyme profile reflected the necessity of the larvae to degrade the fungal substrate, their sole diet, and a probable source of some of the digestive enzymes detected here. When compared to adults, the larvae had a greater diversity and higher levels of enzyme activity, highlighting their importance as the "digestive caste" of the colony.     

Biogeography and endemism of ants (Hymenoptera: Formicidae) in Baja California, Mexico: afirst overview

Abstract Aims Ants (Hymenoptera: Formicidae) of the Baja California peninsula are poorly known, with information based largely on scattered museum and literature records. We provide the first comprehensive account of ant species occurring on the peninsula, we examine distribution patterns, and we assess the ‘peninsular effect’ which predicts that species richness declines from the base to the tip of a peninsula. Location Peninsula of Baja California, Mexico. Methods Data collection involved examining, identifying and recording label data from c. 2350 series of ants. These records provide a provisional, if incomplete, species list. We applied the incidence‐based estimator, Chao‐2, to our data base of specimen records to estimate the total number of ant species on the peninsula. We assessed endemism by comparing our peninsular species list to those from adjacent states. The peninsular effect was tested by comparing genus and species level richness between the two states of Baja California, and across five latitudinal blocks. Results We document 170 native ant species in thirty‐three genera, plus six non‐native species, in Baja California. It seems likely that additional species remain to be discovered: the Chao‐2 estimator of species richness, at 206.0 species, is about 20% higher than our observed species richness. About 30% of the species and 20% of the genera are restricted within Baja California to the relatively mesic California Floristic Province of north‐western Baja California. Nearly all of these species also occur in California. Forty‐seven species (27.6%) are peninsula endemics. Using our entire data set, the peninsular effect appears to be strong, with about twice as many species in the northern state of Baja California than are recorded from the southern state of Baja California Sur; the ratio of genera is 33 to 24. However, this effect becomes weak at the species level and absent at the genus level when minimizing habitat effects by omitting species restricted to the California Floristic Province. At a finer scale, across latitudinal blocks of about 1.9°, the number of species declines towards central portions of the peninsula and then increases in the Cape Region. Nine ant species display strongly disjunct distributions, and these occur in two general patterns: peninsula disjuncts and peninsula–mainland disjuncts. Main conclusions The Baja California peninsula supports a diverse and distinctive ant fauna, with the proportion of endemic species similar to that displayed by plants. Patterns of species and genus richness across the five latitudinal blocks provide poor support for the peninsular effect. Moreover, habitat diversity, especially that related to topographic relief, appears to be the most important factor affecting the gradient of ant species richness in Baja California. Additional collections are needed to develop a more complete species list and to determine the boundaries and status of many species. Nevertheless, the present data base provides a useful starting point for understanding the evolution of ant assemblages in Baja California and for comparison with peninsular patterns in other taxa.