Host nest usurpation and colony foundation in the European amazon ant,Polyergus rufescens Latr. (Hymenoptera: Formicidae)

Summary The socially parasitic mode of founding new colonies by queens of the European amazon antPolyergus rufescens was analysed in the laboratory. Newly-mated females of this obligatory slave-maker were individually introduced into queenright and queenless artificially established colonies of bothFormica cunicularia (the slave present in the natal dulotic nest) andF. rufibarbis (another potentialServiformica host). Particular attention was devoted to the behavioural patterns displayed by these young queens during the usurpation phases. Our observations, supported also by video-taping, show that the slave-making female, before laying her eggs, must penetrate the host colony, kill the resident queen, become accepted by the adult workers and appropriate the host brood. The parasite was almost always adopted in the colonies ofF. cunicularia, whereas in the presence ofF. rufibarbis it was generally killed in a short time. The failure in the attempt of usurping the colonies ofF. rufibarbis is discussed in relation to the host specificity typical of this slave-maker. Finally, egg-laying byPolyergus successful usurpers, the subsequent eclosion of the brood, and its complete social integration in the newly-established mixed colonies were also recorded.     

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.     

Phylogeny and bionomics of Lasius austriacus (Hymenoptera,Formicidae)

Summary Phylogenetic analysis based on sequence data of the mitochondrial COI gene confirms the species status of the recently described Lasius austriacus. The five haplotypes of L. austriacus do not cluster according to their geographic origin, indicating a recent gene flow among the populations. The molecular data corroborate the morphology based hypothesis that L. austriacus belongs to the Lasius (Lasius s.str.) brunneus group. The invasive species Lasius neglectus forms a sister taxon with L. turcicus, both next related to L. austriacus. Other phylogenetic relationships within the genus Lasius are in accordance with morphological data.First data on the bionomics of L. austriacus are discussed in context with its phylogenetic position. Based on gyne and male morphology, excavations of nests, pitfall trapping and observations in formicaries, we hypothesize that L. austriacus is a mainly hypogaeic, monogynous species with nuptial flight. These are characters of the Lasius brunneus group in general, except the polygynous-polycalic, intranidally copulating L. neglectus. Aggression tests, however, revealed non-aggressive behaviour (antennation) between separated L. austriacus populations, but pronounced interspecific aggression against L. neglectus. This confirms the species status of L. austriacus and indicates a reduced level of intraspecific aggression, similar to L. neglectus.The status of L. austriacus as a native species in Central Europe is confirmed.Received 10 February 2003; revised 24 June 2003; accepted 23 July 2003.     

Integration raids in the Amazon ant Polyergus rufescens (Hymenoptera, Formicidae)

Summary. Groups of enslaved Formica fusca workers from mixed colonies of Polyergus rufescens with numerous slave workforce tend to split off and found small and almost homospecific nests around the main nest, with at least some of them connected with the latter with underground passages. Their inhabitants are able, at least temporarily, to adopt young F. fusca gynes. P. rufescens invades these satellite nests in a manner similar to the normal slave raids, and carries the slaves back to the main nest. The supposed evolutionary cause of this behaviour is to keep integrity of mixed colonies and prevent possible emancipation of slaves.Received 18 August 2004; revised 27 September 2004; accepted 11 October 2004.     

Homing Behaviour in Polyergus rufescens Latr. (Hymenoptera,Formicidae)

Homing mechanisms of the European slave-making ant Polyergus rufescens Latr. are investigated by field experiments. The analysis of the behaviour and paths of both homing scouts and raiders after passive displacement showed that: i. Scouts probably home by using a path integration system based on celestial cues; and ii. Displaced raiders do not seem to adopt such a vectorial orientation mechanism. Moreover, we found that passively displaced scouts exhibit a systematic search strategy for the nest after a rectilinear path. By contrast, raiders perform a similar search pattern just after release. Similarities between Cataglyphis and Polyergus homing behaviour are discussed.     

Morpho-functional comparison of the Dufour gland in the female castes of the Amazon ant <Emphasis Type="Italic">Polyergus rufescens</Emphasis> (Hymenoptera,Formicidae)

The Dufour gland is crucially involved in main aspects of the parasite habit of the slave-making ant Polyergus rufescens, i.e. slave-raids and host colony usurpation. Workers use chemicals from this gland as recruitment signals during raid organization, while newly-mated queens use its secretion to appease residents during host nest invasion. Here, we report a comparison of the general morphology and fine structure of the Dufour gland in the female castes of P. rufescens: queens, ergatogynes (intermediate forms), and workers. The analysis clearly shows the link between gland structure and its behavioural role in queens and workers. In particular, queens present a hypertrophied gland with an extended lumen and a thin epithelium no more active in secretory function. This is consistent with the fact that usurper queens use the Dufour gland contents only during the short phase of host nest penetration. Contrary to adult queens, the cytoplasmic organization of the Dufour gland epithelium of raiders is typical for a tissue with secretory activity (abundance of mitochondria, free ribosomes, strands of smooth endoplasmic reticulum and a Golgi apparatus). This is consistent with the continuous raiding activity performed by workers throughout their adult life. The biology of ergatogynes is still an enigmatic matter. Their Dufour gland is intermediate in shape and size between that of queens and workers. It presents a fairly thick epithelium with features that are typical of a quite active secretory tissue.     

Polynesian ant (Hymenoptera: Formicidae) species richness and distribution: a regional survey

Thirteen Polynesian islands, including five true atolls, an uplifted atoll, and seven high volcanic islands of varying ages, were surveyed for ants by hand collecting techniques. Ten of the thirteen islands had been surveyed previously, and more and species were found in the present survey than were known from all earlier surveys combined, with two exception (Ducie Atoll and Easter Island).This represents the first report of the Argentine ant, Linepithema humile Mayr, from Easter Island. L. humile is a very successful pest species which has only recently invaded Easter Island, and is now very abundant and widespread, occurring at 16 of the 17 sample sites scattered across the island. The introduction of this species is almost certainly responsible for the apparent decline in species richness on Easter Island.In general, more species were present on high islands than atolls of a similar size, and elevation was significant while log (area) and latitude were not in a multiple linear regression with ant species number as the dependent variable. Not enough time was spent on the islands to survey their ant faunas completely, and extrapolations from species effort curves and jackknife estimators of earlier, thorough surverys for ants in the society Islands suggest that only about 50% of the total species were collected in the present survey, at least on the high islands. My collections were probably more complete on the atolls. The increase in species numbers from the present survey relative to known species richnesses (particularly when a large fraction of the species actually present were probably not included in the present survey) supports the hypothesis that remote Polynesian islands are not as depauperate in terms of ant species numbers as previously thought.     

Raiding and Foraging Behavior of the Blood-Red Ant,Formica sanguinea Latr. (Hymenoptera,Formicidae)

In this paper we report the results of a detailed study on the behavioral ecology of slave raiding and foraging activity in the European blood-red ant, Formica sanguinea Latr. The field study was conducted over an unbroken period of 78 days, during which the activity of two dulotic colonies of this facultative slave-maker was observed for 10 h each day. It was possible to observe 26 raids distributed over 23 days, among which 18 were followed by the sacking of nests belonging to the species F. cunicularia, F. fusca, and Lasius emarginatus, whereas 8 failed. Simple, continuous, and simultaneous raids occurred. We recorded the timing, frequency, distance, and direction of slave raids, including the number of participants and the type of booty. Particular attention was devoted to the scouting behavior and raiding organization. Moreover, every day, we observed foraging and predatory behavior, during which adult insects (mainly ants), seeds, and berries were retrieved to the dulotic colonies. On the basis of our observations F. sanguinea seems to be a very efficient slave-maker and predatory species of the Raptiformica subgenus. Moreover, its dulotic behavior may be regarded as a continuation and an expansion of its foraging and predatory behavior, as predicted by Darwin's hypothesis for the origin and evolution of slavery in ants.     

Communication in the primitive cryptobiotic ant Prionopelta amabilis (Hymenoptera: Formicidae)

Summary The Neotropical ant Prionopelta amabilis, a cryptobiotic species in the phylogenetically primitive tribe Amblyoponini, lives in subterranean habitats, where it preys preferentially on campodeid diplurans and other small arthropods. Here we report that the species employs chemical recruitment and orientation trails during foraging and nest emigrations. The trail pheromone originates in a hitherto unknown basitarsal gland located in the basitarsus of the hindlegs. Trails are laid by a special foot dragging behavior. During the recruitment process the chemical trail signal is complemented by body shaking on the part of the recruiting ant. Foragers frequently wipe the basitarsal gland opening in the hindlegs with the grooming apparatus of the front legs. This latter structure is equipped with unusual glands evidently specialized for this purpose.     

Relationships between the ant Brachymyrmex obscurior (Hymenoptera, Formicidae) and Acacia pennatula (Fabaceae)

Summary. In central Mexico, the ant Brachymyrmex obscurior Forel feeds on nectar produced by extrafloral nectaries of Acacia pennatula (Schlecht. & Cham.) Benth. However, no studies have determined whether the ants visitation is related to plant nectar availability and whether ants protect A. pennatula from herbivory. The objectives of this 2-yr study (2000–2001) were to assess whether seasonal changes in ant visitation coincide with extrafloral nectar productivity in A. pennatula and to determine whether ants protect the plant. At the end of the dry season (April–June) B. obscurior was the only ant species on A. pennatula and extrafloral nectar production is limited to this period. Exclusion experiments, performed at the end of the dry season showed that A. pennatula did not receive a protective benefit when visited by ants. Branches with ants and branches where ants are excluded had similar numbers of the nonmyrmecophile leafhopper Sibovia sp. which was the only herbivore observed under natural conditions.Received 24 March 2004; revised 4 September 2004; accepted 8 September 2004.     

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.     

Responses of Two Potential Host Species (Formica gnava and Formica occulta) to Pupae of the Obligatory Slave-Making Ant, Polyergus breviceps (Hymenoptera: Formicidae)

Queens of the slave-making ant, Polyergus breviceps, take over nests of adult Formica workers when establishing new colonies. Although naïve to slave-maker brood, the usurped Formica rear Polyergus offspring and nests containing both host and parasite species forms. Host worker acceptance of parasite brood has been attributed to the similarity of brood tending signals between these closely related taxa and/or the presence of an attractive pheromone in the slave-maker brood. By presenting single-species groups of Formica occulta and Formica gnava (two host species of P. breviceps) with a choice of Formica pupae of both species or with a choice of P. breviceps pupae from both types of mixed-species nests, it seems that neither close phylogenetic relatedness nor an attractive brood odor alone can account for the propensity of host workers to adopt slave-maker pupae. Significantly greater numbers of P. breviceps pupae were adopted by enslaved workers than by free-living workers, and within the enslaved groups and the free-living F. gnava group, greater numbers of P. breviceps pupae were adopted if they were from nests where the host species was conspecific to workers used in tests. When presented with F. gnava and F. occulta pupae, Formica workers adopted conspecific pupae almost exclusively and ignored or consumed pupae of the other host species. Taken together, these results imply that P. breviceps pupae have both a species-specific odor and a general brood-tending pheromone, upon which a host odor may be imposed. The disparate requirements of immatures at different stages of development for cue specificity or generality in maintaining nest exclusivity and maximizing inclusive fitness are discussed.     

Trophic eggs laid by fertileMyrmica queens (Hymenoptera: Formicidae)

Summary Most matureMyrmica rubra, M. ruginodis, M. schencki andM. sulcinodis queens lay some trophic eggs in addition to reproductive eggs whether reared alone or attended by workers, and regardless of season. Queen trophic eggs resemble those laid by workers. They are oval, slightly flaccid, opalescent and contain no embryo, and inM. rubra andM. schencki they are significantly smaller than reproductive eggs. Generally, queens lay their first trophic eggs later in the season than their first reproductive eggs.     

Mechanisms affecting load size determination inAtta cephalotes L. (Hymenoptera,Formicidae)

Summary The size of leaf-cutting ant foragers correlates more closely with the weight than the area of the leaf fragments they cut. This implies that the mechanism of load size determination is not a simple function of body geometry. Ants were found not to adjust the radius of cut to compensate for experimental changes in leaf weight during the process of cutting. However, ants changed their cutting behaviour according to the thickness of the region of the fragment being cut. Ants decreased their cut radius when cutting through leaf veins. Similarly, when cutting artificial laminae of varying thicknesses, ants reduced the cut arc radius when traversing thicker regions.Cut radius was not principally controlled by the position of the rear legs nor the overall body length but by mechanisms associated with the head and thorax of the ant.     

Aggregation and adult transportation in disturbed colonies of <Emphasis Type="Italic">Wasmannia auropunctata</Emphasis> Roger (Hymenoptera,Formicidae)

Disturbance of W. auropunctata colonies first produced, as expected, significant dispersal of workers and queens, but this was soon followed by a radiate aggregation of workers, heads to center, in groups of 5 – 8 individuals, all with mandibles widely open. Queens did not aggregate, but instead searched for the grouped workers, antennating the gaster of a selected individual; after this, workers began to slowly board onto the queen’s body. This behavior was repeated with other groups, until the queen could not bear any more workers. This behavior is registered for the first time for adult ants, and is interpreted as a unique strategy to reorganize the nest or to establish a new colony. The open mandibles may indicate the release of alkylpyrazine, a known aggregation pheromone. Received 8 January 2007; revised 28 February 2007; accepted 2 March 2007.     

New synonymy of Proceratium williamsi Tiwari (Hymenoptera,Formicidae)

Proceratium bhutanense De Andrade, 2003, syn. n. is here found to be conspecific with Proceratium williamsi Tiwari, 2000 and accordingly treated as a junior synonym.