Comparison of foraging tool use in two species of myrmicine ants (Hymenoptera: Formicidae)

Many ant species are known to exhibit foraging tool use, during which ants place various debris items (e.g., pieces of soil, leaves, pine needles, etc.) into liquid food, and then they carry the food-soaked tools back to the nest. In the present study, we compared the tool-using behavior in captive colonies of two closely related myrmicine ants with different feeding preferences: Aphaenogaster subterranea, an omnivorous species, and Messor structor, a mainly granivorous seed-harvester species. We supplied foraging ants with honey-water baits and six types of objects they could use as tools: sand grains, small soil grains, large soil grains, pine needles, leaves, and sponges. We found that the workers of A. subterranea both dropped more tools into honey-water baits and retrieved more of these tools than the workers of M. structor. While A. subterranea preferred smaller tools over larger ones, tool preferences for M. structor did not differ significantly from random. In addition, tool dropping was significantly faster in A. subterranea, and both the dropping and retrieving of tools began significantly earlier than in M. structor. For Aphaenogaster species that regularly utilize and compete for liquid food sources, the ability to efficiently transport liquid food via tools may be more important than it is for seed-harvester ants. Dropping tools into liquids, however, may still be useful for seed-harvester species as a means to supplement diet with liquid food during periods of seed shortage and also to serve as a means of getting rid of unwanted liquids close to the nest.

A new species of Epopostruma (Hymenoptera: Formicidae) from monsoonal Australia

Epopostruma is an uncommon genus of myrmicine ants endemic to relatively mesic regions of southern and eastern Australia. Here we describe a new species recently recorded from the ‘Top End’ of Australia’s Northern Territory, E. topendi sp. n. from Melville Island and Nitmiluk National Park. The new species is known from one specimen from each of two sites in the Australian monsoonal tropics, the only records of the genus from this region. This addition brings the number of described species of Epopostruma to twenty.

Queen loss increases worker survival in leaf-cutting ants under paraquat-induced oxidative stress

Longevity is traded off with fecundity in most solitary species, but the two traits are positively linked in social insects. In ants, the most fecund individuals (queens and kings) live longer than the non-reproductive individuals, the workers. In many species, workers may become fertile following queen loss, and recent evidence suggests that worker fecundity extends worker lifespan. We postulated that this effect is in part owing to improved resilience to oxidative stress, and tested this hypothesis in three Myrmicine ants: Temnothorax rugatulus, and the leaf-cutting ants Atta colombica and Acromyrmex echinatior . We removed the queen from colonies to induce worker reproduction and subjected workers to oxidative stress. Oxidative stress drastically reduced survival, but this effect was less pronounced in leaf-cutting ant workers from queenless nests. We also found that, irrespective of oxidative stress, outside workers died earlier than inside workers did, likely because they were older. Since At. colombica workers cannot produce fertile offspring, our results indicate that direct reproduction is not necessary to extend the lives of queenless workers. Our findings suggest that workers are less resilient to oxidative stress in the presence of the queen, and raise questions on the proximate and ultimate mechanisms underlying socially mediated variation in worker lifespan. This article is part of the theme issue ‘Ageing and sociality: why, when and how does sociality change ageing patterns?’

A multi-gene phylogeny of Australian Monomorium Mayr (Hymenoptera : Formicidae) results in reinterpretation of the genus and resurrection of Chelaner Emery

Monomorium Mayr is a speciose, cosmopolitan genus of myrmicine ants that has had a challenging systematic history, comprising numerous lineages whose relationships are problematic. This study employed an extensive sampling of mostly Australian taxa, along with exemplars of other genera of Solenopsidini, to examine relationships among the continent’s Monomorium fauna. Sequences from elongation factor 1α F2, wingless and cytochrome oxidase subunit 1 (COI) were analysed using Bayesian and maximum likelihood methods. The resultant phylogeny resolved Australian Monomorium into two major clades separated by exemplars from other genera; one comprised predominantly species with 11-segmented antennae (corresponding to Monomorium s. str. in a recent study of Myrmicinae) along with three Paleotropical species. The second clade included Australian species with 12-segmented antennae, two New Zealand species and two from New Caledonia. Two Australian cryptobiotic species were resolved as sister to Clade 2. COI analysis indicated that some species (M. fieldi Forel, M. leave Mayr and M. leae Forel) possibly represent cryptic species complexes. The New Zealand M. antipodum Forel was recovered as a valid species, and is closely related to an eastern Australian population. We resurrect the genus Chelaner Emery for species in the second clade (with 12-segmented antennae) and outline morphological characters to separate Chelaner from Monomorium s. str. Fifty-three species of Chelaner are treated as either stat. nov. or stat. rev.

Ants of the Monomorium monomorium species-group (Hymenoptera: Formicidae) in the Arabian Peninsula with description of a new species from southwestern Saudi Arabia

We revise the taxonomy of the myrmicine ants of the Monomorium monomorium species-group for the Arabian Peninsula. Six species are recognized: Monomorium aeyade Collingwood & Agosti, 1996, M. clavicorne André, 1881, M. exiguum Forel, 1894, M. holothir Bolton, 1987, M. mohammedi sp. n., and M. sarawatense Sharaf & Aldawood, 2013. On the basis of the worker caste, we describe Monomorium mohammedi sp. n. from the southwestern region of the Kingdom of Saudi Arabia (KSA). We designate a neotype for Monomorium aeyade Collingwood & Agosti and redescribe and illustrate the worker caste. Furthermore, we provide a worker-based species identification key, distribution maps for the treated species, and ecological and biological notes, if available. Monomorium holothir is recorded for the first time from the KSA. Also, we propose M. clavicorne var. punica Santschi, 1915a as a junior synonym of M. clavicorne, as well as M. dryhimi Aldawood & Sharaf, 2011 and M. montanum Collingwood & Agosti, 1996 to be treated as junior synonyms of Monomorium exiguum.

Genital Morphology of Winged and Wingless Males in the Ant Genus Cardiocondyla (Formicidae, Myrmicinae)

The myrmicine ant genus Cardiocondyla is characterized by a peculiar male diphenism with winged disperser males and wingless, “ergatoid” fighter males. Here we describe and illustrate the morphology of the male external genitalia of 13 species of this genus. Several characters, especially the parossiculus of the volsella and the medial face of the paramere, vary between different species groups and might be useful to clarify the infrageneric taxonomy of Cardiocondyla. External genitalia between different phenotypes of a species differ primarily in size. All examined males, both winged and ergatoid, have a parameral hook that resembles a structure described in Nesomyrmex males but apparently is absent in other studied myrmicine ants. The presence and absence of this hook might be useful for future studies on the relationships within the myrmicine tribe Crematogastrini.

Kempfidris, a new genus of myrmicine ants from the Neotropical region (Hymenoptera: Formicidae)

The new genus Kempfidris gen. nov. is described based on the workers of a single species, K. inusualis comb. nov., from Brazil, Ecuador, and Venezuela. Kempfidris inusualis comb. nov. was originally described by Fernández (2007) and provisionally placed in Monomorium awaiting a better understanding of the internal relationships in Myrmicinae. Kempfidris gen. nov. has a series of distinctive morphological characters including the mandibular configuration, vestibulate propodeal spiracle, propodeal carinae, and cylindrical micro-pegs on the posteromedian portion of abdominal tergum VI and anteromedian portion of abdominal tergum VII. This last trait appears to be autapomorphic for the genus.