Chemical and ethological studies of the trail pheromone of the ant Manica rubida (Hymenoptera: Formicidae)

ABSTRACT. The poison gland of Manica rubida contains nanogram quantities of four alkylpyrazines, methylpyrazine, 2,5-dimethylpyrazine, trimethylpyrazine and 3-ethyl-2,5-dimethylpyrazine, of which only the last induces pronounced trail-following behaviour. Myrmica rubra and M. rubida workers follow each other's trails equally well when allowance is made for the much greater size of M. rubida workers. The cross activity in trail-following between M. rubida, M. rubra and Tetramorium caespitum is understandable in terms of the amounts and proportions of the different pyrazines present in their glands and their responses to the synthetic substances and appropriate mixtures of them.     

Army ant behaviour in the poneromorph hunting ant Onychomyrmex hedleyi Emery (Hymenoptera: Formicidae; Amblyoponinae)

Onychomyrmex belongs to the phylogenetically basal ant tribe Amblyoponini but shows prototypical army ant behaviours, i.e. group predation and nomadism. In order to investigate these behaviours, Onychomyrmex hedleyi was observed in the field and in laboratory experiments. Workers of O. hedleyi would frequently hunt centipedes but rarely social insects. Workers did not dismember the victims but recruited the colony mates to conduct group retrieval. If the prey were too large or too heavy to retrieve, the entire colony moved from the bivouac site to the prey site. Although foraging on the forest floor, a colony repeated the extension and withdrawal of a raiding column, which was up to 80 cm long (mean ± SD, 41.6 ± 18.5 cm). Colonies were nomadic and the relocation distance was up to 150 cm (mean ± SD, 74.4 ± 45.0 cm). Retinues guarded a queen who moved to a new bivouac site in the early phase of relocation. Colonies were found to stay at a site statistically longer if they had come from a more distant site, and were also observed to move to a more distant site if they had spent a longer time at a particular bivouac site. The consecutive migrations did not show significant directionality.     

An experimental analysis on the magnetic field sensitivity of the black-meadow ant Formica pratensis Retzius (Hymenoptera: Formicidae)

Ant responses were tested under both the natural geomagnetic and artificially induced Earth-strength electromagnetic field. Foragers were trained for a month to visit a food source at the north arm accessed through an orientation platform assembly. Under the natural geomagnetic field, when all other orientational cues were eliminated, results indicated significant heterogeneity of ant distribution with the majority seeking geomagnetic north in darkness. However, in light, foragers failed to discriminate geomagnetic north. Under shifted artificial electromagnetic field, orientation was predominantly on the artificial magnetic N/S axis with a significant preference for the artificial north in both light and dark conditions.     

Transmission of Vairimorpha invictae (Microsporidia: Burenellidae) infections between red imported fire ant (Hymenoptera: Formicidae) colonies

Red imported fire ant, Solenopsis invicta, colonies were successfully infected with the microsporidium Vairimorpha invictae by introducing live larvae, pupae, or dead adults from V. invictae-infected field colonies collected in Argentina. Introductions with 4th instar larvae or non-melanized pupae obtained from infected field colonies, resulted in infection of 40% of the inoculated colonies. Introductions of 4th instars or melanized pupae produced from colonies that were initially infected in the laboratory, resulted in infections of 83% of the colonies, thus perpetuating the infection in other colonies. Infection was detected in 2 of 6 colonies after introducing adult worker caste ants that had died with V. invictae. The average number of adults and the volume of immature ants per colony were significantly lower in the infected than in the control colonies. Infected colonies had 86% fewer adults per colony and 82% less immature ants than the controls. A portion of the 16S rRNA gene of the V. invictae identified from these studies was amplified, cloned, and sequenced; the 1251 nucleotide amplicon was 100% identical to the 16S rRNA gene sequence recorded previously in the GenBank database, thus verifying the species as V. invictae. This is the first report of the artificial transmission of this pathogen to uninfected ant colonies, and demonstration of its ability to hinder growth in individual colonies.     

The antimicrobial activity of the mandibular gland secretion of a formicine ant, Calomyrmex sp. (Hymenoptera: Formicidae)

The mandibular gland secretion from mature workers of the formicine ant Calomyrmex sp. exhibits strong antimicrobial activity when tested against selected soil microorganisms. The activity against bacteria is both inhibitory and bacteriocidal while that against fungi is inhibitory. The white secretion from young workers appears to be much weaker in its antibiotic effects.     

Mutual interference: Behavioural consequences of encounters between adults of the parasitoid wasp Venturia canescens (Hymenoptera; Ichneumonidae)

Adult Venturia canescens were observed under conditions of increasing parasitoid density. Their behaviour was classified into three main categories: probing, walking and resting. Encounters between adults were recorded as they occurred. The percentage of time spent probing did not decline with density as had been found previously. This is because encounters between wasps have a number of different effects, some of which cancel each other out. These encounters (a) alter the frequency with which the insects change their behaviour (increasing the number of changes during probing or resting; decreasing the number of changes during walking), and (b) affect the choice of behaviour pattern to which the wasp changes. The interference relationship is therefore not due to decrease in available searching time; nor is there any evidence for encapsulation (an immunity reaction of host larvae to parasitoid eggs), pseudo-interference, or time-wasting due to avoidance of superparasitism. It is suggested that the violent behavioural reaction of a host larva to attack could cause eggs to be lost in the medium, and thus affect searching efficiency.     

Microsatellite genotyping of red imported fire ant (Hymenoptera: Formicidae) colonies reveals that most colonies persist in plowed pastures

Our study focused on colony dynamics of the red imported fire ant, Solenopsis invicta Buren (Hymenoptera: Formicidae), in relation to the standard practice of planting rye grass (i.e., plowing) in the fall in Louisiana. Microsatellite molecular markers were used to determine genotypes of individuals from red imported fire ant colonies. These markers allowed us to monitor treatment effect by detecting changes in number and location of colonies in response to disking of pasture plots. Previous research on mound disturbance as a form of cultural control in pastures has produced mixed results. We found that the majority of colonies persisted on plots after plowing. Mound density and mound area, 5 mo after plowing, were not significantly different among treatments. In contrast, April measurements of mound volume were significantly smaller on plowed plots compared with control plots. A closer look at the rebuilding of mounds on plowed plots, during the 5 mo, showed that mound heights stayed below pretreatment measurements and they were significantly smaller than those of undisturbed mounds. Whether plowing has potential for use as a cultural control technique in reducing the impact of red imported fire ant mounds on agricultural practices in pastures remains to be seen. Conceivably, the best application of this technique will be in combination with other control measures in an integrated pest management approach to control red imported fire ants in pastures.     

Lenomyrmex, an enigmatic new ant genus from the Neotropical Region (Hymenoptera: Formicidae: Myrmicinae)

Abstract. We describe a new myrmicine ant genus, Lenomyrmex , with four new species: L. mandibularis (type species) and L. foveolatus from Colombia, L. wardi from Ecuador and Colombia, and L. costatus from Panama. The new taxon is clearly distinguished from other myrmicine ants by the following combination of characters: (1) mandibles elongate-triangular, with crenulate masticatory margin three times longer than basal margin, and bearing a series of ten to twenty minute peg-like denticles that arise along and immediately behind the masticatory margin; (2) frontal lobes poorly expanded laterally, partly covering the antennal fossae; (3) large and deep antennal fossae; (4) antennal scrobes absent; (5) eyes protuberant; (6) petiole pedunculate, with poorly defined node and with an anteroventral subpetiolar process pointed anteriorly. The affinities of this new taxon within Myrmicinae remain unclear and the observed characters do not permit it to be included satisfactorily in any of the known tribes or genus groups of the subfamily.     

An experimental analysis of pleometrotic advantage in the desert seed-harvester antMessor pergandei (Hymenoptera; Formicidae)

Summary Starting colonies of the desert seed-harvester antMessor pergandei are clumped in the field and face severe intraspecific competition through brood raiding. Single foundress laboratory colonies ofM. pergandei are more likely to succeed at brood raiding with conspecific colonies if they are given additional workers and mature pupae several days prior to brood raiding. Per foundress fecundity remains constant across laboratory starting colonies established with 1, 3 and 5 foundresses. These results suggest that the selective advantage of cooperative colony foundation (pleometrosis) in this and similar species may derive directly from the ability of multiple foundresses to produce a larger brood raiding force.     

Functional analysis of the myrmecophilous relationships between ants (Hymenoptera: Formicidae) and lycaenids (Lepidoptera: Lycaenidae)

Summary Mature larvae of the myrmecophilous lycaenid Polyommatus coridon produce an average of 30.9 droplets of a honeydew-like secretion per hour. They occur in population densities of about 20/m². The volume of secretion over the whole larval period is estimated to be 22–44 l with an energy content of 55–110 J. Thus, P. coridon larvae produce carbohydrate secretions with an energy equivalent of 1.1–2.2 kJ/m². Using data from the literature on ant metabolism, it is shown that these carbohydrate secretions may contribute significantly to the nutrition of attending ants. The myrmecophilous relationship between the larvae of P. coridon and ants should therefore be regarded as a mutualistic symbiosis.     

Queens defense by workers in the highly polygynous ant Crematogaster pygmaea (Hymenoptera: Myrmicinae)

Some aspects of the biology of Crematogaster pygmaea, a highly polydomous and polygynous ant, are more commonly found in monogynous species. One such characteristic is the high attractiveness of its queens. In this study, this attractiveness was assessed under varying experimental conditions to investigate the factors responsible for its expression and variation, and to identify the nature of queen attractiveness. It was shown (1) that C. pygmaea queens are highly attractive to the workers that cluster on and around them (retinue), (2) that the attractiveness of C. pygmaea queens is context-dependent, i.e., it increases with increasing degree of potential danger to the queen, (3) that the attractiveness signal of C. pygmaea queens is chemically based, and (4) that this signal is persistent and apparently not colony-specific. The proposed hypothesis is that the C. pygmaea queens constantly release an attractiveness signal that is “read” by the workers, in a dependent way linked to the context, and that the main function of this attractiveness is to protect queens. This protection would have a high adaptive value in the context of the social structure and the reproductive strategies in C. pygmaea.     

Status of the exotic ant <Emphasis Type=Italic>Nylanderia flavipes</Emphasis> (Hymenoptera: Formicidae) in northeastern Ohio

In 2005, the non-native Nylanderia flavipes was first recorded from Ohio. Here, we present the results of a baseline study designed to assess the status of this exotic species in northeastern Ohio and to explore its potential impacts on local ant communities and the extent to which it has been incorporated into the diet of a native predator, the red-backed salamander. At the sites where N. flavipes occurred, we found a sixfold increase in total ant abundance, with 87% of all ants collected being N. flavipes. The high numerical dominance of N. flavipes did not lead to observable changes in the species richness and abundance of the native ant community. At baits, N. flavipes did not engage in interspecific combat and did not exhibit aggression towards native ants. Thus, aggression and interference competition are not likely factors explaining the high local abundance of N. flavipes. Red-backed salamanders have incorporated N. flavipes into their diet, but further research is needed to understand the interactions of N. flavipes within the forest-floor food web. Although we did not detect changes in the local ant communities in the presence of N. flavipes, we argue that this species’ high local abundance and ability to forage at cooler temperatures may give it a competitive advantage and thereby affect native ants through exploitative competition.     

Molecular phylogenetic analysis of the ant genus <Emphasis Type="Italic">Formica</Emphasis> L. (Hymenoptera: Formicidae) from Palearctic region

Sixty-five sequences of the mitochondrial DNA cytochrome b gene fragment (759 bp) and 23 sequences of the NADH dehydrogenase subunit 6 gene fragment (224 bp) were compared in ants of the genus Formica L. from different regions of the Palearctic and in Polyergus rufescens Latr. as outgroup. In total, 28 species of the genus Formica were examined. As a result, dated trees with a molecular clock were constructed showing the phylogenetic relationships of Formica ants. The topology of the obtained tree based on the Cyt-b sequences was found to be not consistent with the generally accepted opinion on the Formica rufa and F. rufibarbis groups. New data on the formation history of the present-day fauna of Formica ants of the Palearctic were obtained. It was demonstrated that a considerable fraction of the examined species (about a third) were formed in the Quaternary Period.     

Mixed colonies and hybridisation of <Emphasis Type="Italic">Messor</Emphasis> harvester ant species (Hymenoptera: Formicidae)

The Mediterranean harvester ant species Messor minor, M. cf. wasmanni, and M. capitatus can co-occur in the same habitat. In Italian populations, we encountered colonies that contained workers from more than one species as identified via standard morphology, as well as colonies with workers that appeared to be morphologically intermediate between species. This unusual finding required further analysis. We analysed such colonies using microsatellites, mitochondrial DNA and refined morphometrics, and a simple inference key for the colony-level interpretation of data from the three sources combined. We infer that Messor minor and M. cf. wasmanni engage in bidirectional interspecific gene flow. Hybrids between these two species are inferred to produce fertile offspring, which would indicate that barriers to hybridisation do not exist or can be completely overcome. This is unexpected, given that they are non-sister species and broadly sympatric in nature. Our findings also indicate the possible occurrence of hybrid-hybrid crosses, a phenomenon rarely observed in ants. We cautiously interpret the data at hand as in support of the interspecific gene flow considerably shaping the genetic makeup of populations, raising the question about a potential adaptive value of this hybridisation. Messor capitatus mixes with hybrids of the other two species, but we found no indication of hybridisation involving this species. We discuss various hypotheses on the causations of colony mixing and hybridisation in the three Messor species at the proximate and ultimate level.     

Palladium(II) amido complexes with an unsymmetrical PNP′ pincer-type coordination and a new (E,E)-tetradentate diphosphinoazine coordination mode

Cationic palladium(II) complexes [PdCl{PR₂CH₂C(Bu^t)NNC(Bu^t)CH₂PR₂}]Cl, where R = isopropyl, cyclohexyl or tert-butyl, were synthesized by the reactions of the corresponding diphosphinoazines with bis(acetonitrile)palladium(II) dichloride. When bis(benzonitrile)palladium(II) dichloride was used instead, in the molar ratio of 2:1 to the diphosphinoazine, a new complex was isolated with the isopropyl ligand showing a previously unknown (E,E) tetradentate coordination mode. Crystal and molecular structure was determined by X-ray diffraction. The solid complex was a racemate of two axially chiral enantiomers and the chirality was preserved in solution. Reactions of the cationic complexes with triethylamine gave complexes [PdCl{PR₂CHC(Bu^t)NNC(Bu^t)CH₂PR₂}], containing deprotonated diphosphinoazines in ene-hydrazone unsymmetrical pincer-like configuration. The complexes represent several of the still rare examples of Pd(II) amido bis(phosphine) complexes with a chlorine atom covalently bonded trans to the amide nitrogen.