Ergatoid Queens Research Articles

Colony composition and morphological caste differentiation between ergatoid queens and workers in the ponerine ant genus Leptogenys in the Oriental tropics

Colony composition and morphological caste differentiation between queens and workers were studied in 14 Leptogenys species collected in Malaysia and Indonesia. Ten species had ergatoid queens and four species reproduced by mated workers without morphologically distinct queens. Colonies of most species having ergatoid queens were monogynous, however, polygyny was found in two species. In contrast, all four species which reproduced by mated workers (= gamergates) were polygynous. Degree of caste differentiation between ergatoid queens and workers was conspicuous in L. myops. In the other species, the head width of ergatoid queens was almost the same as in their conspecific workers, although, the abdomen was generally wider in ergatoid queens than in workers. The workers of ergatoid species have almost the same number of ovarioles as their queens except for L. myops, however, spermathecae were remarkably reduced in length or missing. All workers in the four species that reproduced with gamergates had spermathecae which were smaller than those of ergatoid queens.

Morphology and reproductive behaviour of intercastes in the ponerine antPachycondyla obscuricornis

Queens are usually the functional reproductives inPachycondyla obscuricornis, but none were found in one colony collected near Brasilia. In this colony, three adults differed morphologically from workers; although wingless, their thorax was more or less like that of winged queens (scutum and scutellum distinct; metanotum larger than that of workers). Another 11 such individuals were found by opening cocoons. We consider that these are intercastes (sensu Peeters, 1991). Two adult intercastes were mated and laid eggs. In contrast, all the workers were virgin, but some laid distinct trophic eggs which were fed to the two reproductives. Following experimental removal of the intercastes, dominance interactions began among the workers, and reproductive eggs were then laid. Intercastes with a reproductive function have not been reported previously in the Ponerinae. They are distinct from ergatoid queens (permanently wingless reproductive caste) or gamergates (mated egglaying workers).

Colony Characteristics of the Indonesian Myrmicine Ant Myrmecina sp. (Hymenoptera, Formicidae, Myrmicinae): Polygynous Reproduction by Ergatoid Queens

Colony composition of Myrmecina sp. A, which has a specialized myrmecophilous oribatid mite Aribates javensis Aoki, Takaku, & Ito, was studied in Bogor, West Java, Indonesia. The colonies had no alate or dealate queens. Alternatively, an average of 8 ergatoid queens, who were easily distinguished from workers in width and length of the 4th abdominal tergaite, mated and laid eggs. Males were frequently produced in many colonies, but, production of ergatoid queens was observed in only 2 of 24 colonies in the field. Expulsion of some old ergatoid queens by workers was observed after emergence of new ergatoid queens in one colony. Experimental evidence confirmed the presence of queens had the negative effect on production of new ergatoid queens.

Worker Polymorphism in the Red-Head Bulldog Ant (Hymenoptera: Formicidae), with Description of Nest Structure and Colony Composition

Five nests of Myrmecia froggatti were dug out in the dry Eucalyptus woodland around Mt. Gournet, Queensland, northern Australia. Nest structure was simple; a single, vertical unbranched shaft that connected 6-12 chambers down to 80-145 cm. Colonies were monogynous and of small size; each contained one ergatoid queen, an average of 38 workers, and several brood. Ergatoid queens had a sperm-filled spermatheca and between 15-18 ovarioles, whereas workers had an empty spermatheca and 4-15 ovarioles. Pronotum width and head width of workers showed isometric growth. However, allometric growth was observed between the width of the pronotum and the width of the fourth segment of the abdomen. Number of ovarioles was positively correlated with the abdomen width. Thus, large sized workers had a disproportionally larger number of ovarioles than smaller sized workers. The function of large workers of M. froggatti is discussed.

Exocrine glands and the attractiveness of the ergatoid queen in the ponerine antMegaponera foetens

Queens inMegaponera foetens are permanently wingless. In a colony from Kenya we observed that the ergatoid queen was often surrounded by a large number of workers, all conspicuously facing her. To investigate the nature of this attraction, we divided the colony in half. When the queen was transferred from one group to the other, a large court of workers formed immediately. When marked workers were transferred from the queenright group to the other, they attracted much attention and were licked repeatedly. These data suggest that the queen produces a chemical signal which attracts workers, and this signal is transferred onto the workers. In a histological investigation of queen and workers, we found many intersegmental glands in both castes. However, only the queen had a thick glandular epithelium lining her entire body, and this may be the source of her signal. The numerous erect setae covering the queen (but not the workers) may help to dispense the secretions. Our results confirm that ergatoid queens in the Ponerinae are morphologically specialized, despite their external similarity with workers.

Group hunting in a ponerine ant, Leptogenys nitida Smith.

Field observations on the emigration and foraging behaviours of the southern African ponerine ant, Leptogenys nitida, were undertaken at Mtunzini, Natal, South Africa. These colonies have a single ergatoid queen and 200-1000 workers. The nest sites are found in the leaf litter and these nests are moved frequently over distances ranging from 0.5 to 5 m. Leptogenys nitida is a diurnal predator of arthropods dwelling in the leaf litter. Up to 500 workers participate in each foraging trail, and are not led by definite scouts. Ants form clear trunk trails and fan out at various intervals to search for prey. The prey is searched for and retrieved cooperatively. From laboratory tests it was determined that ants will follow pygidial gland extracts, with the poison gland extract eliciting a limited response. The type of army ant behaviour observed in L. nitida seems to be different to that observed in other ponerine ants.

Evolutionary trends in the reproductive biology of ponerine ants (Hymenoptera: Formicidae)

The colony sizes and ovariole numbers of eight ponerine, one cerapachyine and one doryline species are reported. The ergatoid queens of five of these species are described briefly. Workers of the Hypoponera, Leptogenys and Anochetus species entirely lack ovaries, the first report of obligate sterility in this subfamily. Three evolutionary trends in the reproductive biology of the Poneriae are discussed: an increase in ovariole numbers and specialization for reproduction in the queen caste; worker sterility and increasing reproductive differentiation between the castes; and the evolutionary loss of specialization for dispersal in ergatoid queens.

Colony foundation inPlectroctena mandibularisF. Smith, and the evolution of ergatoid queens inPlectroctena(Hymenoptera: Formicidae)

Existing models of the evolution of worker-like morphology in queen ants postulate that the condition arose as a by-product of assisted colony foundation. Under laboratory conditions, two lone, ergatoid queens of Plectroctena mandibularis were able to raise broods to at least the pupal stage without the assistance of other ants. Although these results need to be confirmed under field conditions, they indicate the possibility of a different, additional evolutionary pathway to wingless, worker-like queens in this species. Several possible pathways are discussed.

Ergatoid queens and intercastes in ants: Two distinct adult forms which look morphologically intermediate between workers and winged queens

Summary The term "ergatogyne" is used in ants to describe permanently-wingless female adults which are "morphologically intermediate" between workers and winged queens. This definition is ambiguous because there are two distinct categories of "ergatogynes": ergatoid queens and intercastes. Both have an external appearance (ocelli and alitrunk structure) which combines traditional queen and worker characters, and thus can be confused if they both function as reproductives however intercastes in most species cannot reproduce. Ergatoid queens have replaced winged queens in a substantial number of species. They are sometimes externally similar to conspecific workers, especially in various ponerine species which exhibit limited size dimorphism between castes. Ergatoid queens retain the specialized attributes of a reproductive caste, including larger ovaries, and they are always the functional egg-layers in a colony. In contrast, conspecific intercastes represent various graded stages in a series connecting workers and winged queens, and they occur together with the queens. These hybrid phenotypes result from deviations from the normal pattern of caste differentiation during larval development. Intercastes generally lack a spermatheca and have no reproductive function; however they can mate in a few leptothoracine ants, and then reproduce instead of winged queens in a proportion of colonies.

Soziale Organisation und Fortflanzung bei Ocymyrmex foreliFormicidae-Myrmicinae)

Colonies ofOcymyrmex foreli contained 16–1586 adults of which 4–20% were ergatoid queens the remainder being sterile workers. Each colony contained one inseminated ergatoid queen only and colonies were monogynous. Workers and virgin queens were similar in size and appearance but had distinctive ovaries; queens had significantly more ovarioles than workers, with mated queens having more ovarioles than virgins.

Worker laying in the absence of an ergatoid queen in the ponerine ant genusPlectroctena

Ergatoid queens (without wings and worker-like) occur in Plectroctena mandibularis and P. conjugata. Five nests of these species were incompletely excavated, and an ergatoid was collected in only one of them. The orphaned groups of workers were kept in the laboratory for several months, during which time many eggs were laid. Some of these developed into males. Thus workers can lay haploid eggs in the absence of an ergatoid queen. This was confirmed by dissecting 60 workers from various nests: many of them had mature oocytes in their ovaries, and inseminated individuals were not found. Various data on foraging behaviour and male activity are also presented.

The migrating herdsman Dolichoderus (Diabolus) cuspidatus: an ant with a novel mode of life

The Malayan ant Dolichoderus cuspidatus lives in obligatory symbiosis with the pseudococcid Malaicoccus formicarii and other species of the same genus. The assemblies, which may be encountered up to 25 m away from the nest, are constantly covered with a great number of worker ants who protect them and receive honeydew. In the event of heavy rain the workers from a dense protective cluster, clinging to each other on top of the mealybugs. Neither hunting behavior nor active search for protein sources was observed in D. cuspidatus, although dead insects were accepted as food. When not searching for new plants, the activity of the ants outside the colony is limited to visiting the mealybugs. During the night and parts of the day the ants stay in their nest. Ant colonies deprived of their mealybugs are not viable due to their dependence on the symbiosis and because of the competition of other ants. Antless M. formicarii are likewise not viable. The mealybugs are extremely polyphagous and feed on many different monocotylous and dicotylous angiosperms. They feed exclusively on the phloem sap of young plant parts which are rich in amino acids. Dolichoderus cuspidatus workers carry the mealybugs to such locations. During the picking up and carrying process both partners display typical behavioral patterns. The colonization of new feeding sites takes place in well organized mass processions. During the foundation or disintegration of large feeding complexes, provisional depots with waiting mealybugs and ants are set up. The pseudococcids are carried not only while shifting the feeding sites, but also whenever the colony leaves its former nesting site and especially when any kind of disturbance occurs. They are even carried about without any apparent external cause, which leads to the fact that, at all times of trail activity, on average more than 10% of all ants using the trails carry mealybugs. Mealybugs are also present within the nest, especially adult females which are viviparous and give birth to their offspring there. Censused colonies each consisted of over 10 000 workers, about 4000 larvae and pupae, more than 5000 mealybugs and one ergatoid queen. Male winged ants were observed in large numbers during the dry season (January–February) and during the rainy season (September–October). The colonies form typical clumplike bivouac nests consisting of clusters of workers clinging to each other, thereby covering the brood and the mealybugs. The nesting site is in no way altered by constructive measures and is mostly found close to the ground. The preferred nesting sites are clusters of leaves, and cavities in wood or soil, although a freely hanging bivouac between a few branches may be set up as well. As soon as the distance between the nest and the feeding site is too great the colony moves to the feeding site, whereby the brood and the mealybugs are carried along in a well organized manner. During such nest-moving the establishment of intermediate depots can be observed. A shift of nest sites can also be induced by disturbances or by a change in the microclimate in the vicinity of the nest. Colonies multiply by budding. The tropical rain forest continuously offers different sprouting plants, the utilization of which requires extreme mobility on the part of the consumer. The unique behavioral strategy of D. cuspidatus, to carry constantly their polyphagous mealybug partners to new feeding sites and to take the whole colony there has enabled this ant and its symbiont to occupy this rich food niche. Dolichoderus cuspidatus is the first true nomad found in ants.

THE ANT GENUS CERAPACHYS F. SMITH OF JAPAN, WITH DESCRIPTION OF A NEW SPECIES (HYMENOPTERA, FORMICIDAE)

Two species of the ant genus C e r a p a c h y s of Japan are treated; one of which, C. humicola, is described and illustrated as new based on the worker, the ergatoid queen and the male. The distribution of Japanese Cerapachys is mapped. The genus Cerapachys was established by F. Smith in 1875 based on a single type species C. antennatus F. Smith from Sarawak. This genus is characteristic of the robust antenna1 scape, the box-like trunk, the large first gastric segment (abdominal IV), the presence of the tibia1 spur of middle leg and the denticulate margination of the pygidium. Brown (1975) listed 137 world species of the genus in his revision. The genus Cerapachys belongs to the subfamily Cerapachyinae, which is sometimes placed as a tribe within the subfamily Ponerinae by some authors (Brown, 1975 et al.). In Japan, the genus has been represented by only a single species C. biroi Fore1 from the Ryukyus (Wilson & Taylor, 1967). In this paper another species, C. humida, is described and illustrated as new from the southern area of Japan. Additionally, notes on the distribution of Japanese Cerapachys are given. Measurements, indices and their abbreviations follow Brown’s definitions (Brown, 1975). Before going further I wish to express my sincere thanks to Prof. Y. Hirashima and Assoc. Prof. K. Morimoto, Entomological Laboratory, Kyushu University, Fukuoka, for their constant guidance. I am very grateful to Dr . M. Kubota, Odawara, Mr. K. Masuko, Tokyo Metropolitan University, Tokyo, Mr. H. Sakai, Ashigara and Mr. M. Terayama, Utsunomiya University, Utsunomiya, for their kindness in offering valuable materials. My thanks are also due to Dr. R. Sonobe, Imaichi, for his useful information. * Contribution from the Entomological Laboratory, Faculty of Agriculture, Kyushu University, Fukuoka (Ser. 3, No. 136).

Caste polymorphism inHarpagoxenus canadensis M. R. Smith (Hym. Formicidae)

The European slave-making antHarpagoxenus sublaevis has an unusual female polymorphism. In addition to ordinary workers, there are two kinds of reproductive females, the very rare full queens and the much more common ergatoid (i. e. workerlike) queens. A genetic mechanism is responsible for the development of larvae into either ergatoid or full queens. Sixty-one colonies of the closely related North American speciesHarpagotenus canadensis were collected from several localities in the provinces of Ontario and Quebec, Canada, and a total of 241 workers, 30 intermorphs, and 26 dealate full queens were dissected in order to discover whether a similar polymorphism occurs in this species. However,H. canadensis was found to have an essentialy normal polymorphism. All the fecundated reproductive females that we found were dealate full queens. A spermatheca, which constitutes the only significant difference between ergatoid queens and workers inH. sublaevis, is absent in all workers and intermorphs ofH. canadensis. In addition, we found that colonies ofH. canadensis are monogynous (likeH. sublaevis). However, minority of workers and intermorphs lay eggs even in queenright colonies. The average number of ovarioles is much lower inH. canadansis workers than in those ofH. sublaevis; but, in both species, it varies over about the same range (table IV). In this respect,H. canadensis workers resemble more closely the workers of the host species. The number of Malpighian tubules is five in both the reproductive females and workers. The poison gland is about the same size in bothHarpagoxenus species, but the Dufour's gland inH. canadensis is considerably smaller than inH. sublaevis. Thus, in several respects,H. canadensis bears a closer resemblance to the common host genusLeptothorax (subgenusMychothorax) thanH. sublaevis does.