Seasonal polydomy in a polygynous supercolony of the odorous house ant,Tapinoma sessile

Abstract 1. The odorous house ant, Tapinoma sessile, is a native ant species common throughout North America. In its natural habitat, T. sessile is a low‐key species that consists of small colonies. In invaded urban areas, T. sessile exhibits extreme polygyny and polydomy and becomes a dominant invasive pest. 2. The current study examined: (i) the density, persistence, and the spatial distribution of nests in a large supercolony of T. sessile, (ii) trail abundance and overall colony connectivity as facilitated by the network of trails, (iii) the abundance and the spatial distribution of competing ant species, and (iv) the effect of environmental factors on the number and distribution of T. sessile nests. 3. A distinct pattern of seasonal polydomy was observed, whereby the colony undergoes an annual fission‐fusion cycle. The colony occupies one or a few nests during the winter, experiences rapid exponential growth in the spring to colonize available nesting sites, reaches maximum nest density in the summer, and again coalesces in the winter, returning to the same winter location year after year. The trails show spatio‐temporal variation as well, depending on the location of nesting and foraging sites. Furthermore, nest movements may be driven by soil microclimate and proximity to man‐made structures. 4. In total, 119 ant nests were discovered in a 3.15 ha plot, 90 (76%) of which belonged to T. sessile. Tapinoma sessile exhibited strong colony connectivity as 78/90 (87%) of nests were connected to at least one other nest by a trail. Mean persistence time for T. sessile nests was 133 ± 5 days. 5. Results indicate that T. sessile is a highly adaptable native ant species that exhibits a high degree of flexibility in its colony social structure. A high degree of polygyny and polydomy may contribute to its ecological dominance and pest status in urban environments.     

Lay eggs, live longer: division of labor and life span in a clonal ant species

Abstract Due to a trade-off between reproduction and life span, highly fertile individuals often live shorter lives than nonreproductive conspecifics. Perennial eusocial insects are exceptional in that reproductive queens live considerably longer than the nonreproductive workers. The two female castes may differ strongly in morphology, ontogeny, physiology, diet, behavior, and mating, and all these differences could be responsible for life span differences. In the ponerine ant Platythyrea punctata , morphological and ontogenetic caste differences do not exist. Instead, all workers are capable of producing diploid offspring through thelytokous parthenogenesis, and colonies are essentially clones. Here, we show that reproductives live significantly longer than nonreproductive workers. Reproductives stay in the nest during their whole life, whereas nonreproductives switch from intranidal tasks to foraging when they get older. Different work load and different hormone titers might proximately underlie the different life span of reproductives and nonreproductives in this ant.     

Ocurrence of the antibiotic producing bacterium Burkholderia sp. in colonies of the leaf-cutting ant Atta sexdens rubropilosa

Fungus garden material from recently established Atta sexdens rubropilosa colonies (6-12 months old) was sampled to detect antibiotic producing microorganisms that inhibited the growth of pathogens of insects and of the fungus gardens but did not affect their mutualistic fungus. A bacterium with activity against the entomopathogenic fungus Beauveria bassiana was isolated from 56% of the gardens tested (n=57) and identified from its biochemical profile and from 16S and 23S ribosomal DNA sequences as a member of the genus Burkholderia. The ant-associated Burkholderia isolates secreted a potent, anti-fungal agent that inhibited germination of conidia of the entomopathogenic fungi B. bassiana, Metarhizium anisopliae, of the saprophytic Verticillium lecanii, and also of a specialist fungus garden Escovopsis weberi. Growth of the ant's mutualist fungus was unaffected.     

The cashew nut, Anacardium occidentale (Anacardiaceae), and its perennial association with ants: extrafloral nectary location and the potential for ant defense

Cashew nut trees are consistently ant-visited throughout the year, with the ants attracted to a large number of extrafloral nectaries on the leaves, inflorescences, flowers, and developing nuts. The commercial production of cashew nut, for example, in India, Brazil, and east Africa, consistently applies pesticides, especially insecticides, in large monoculture plantings. Each year prophylactic spraying begins with the first flush of new leaves, continues through flowering, ending at about mid-nut development. We surveyed for ant diversity in sprayed and unsprayed cashew monocultures of various sizes and ages in Sri Lanka, India, and Malaysia to document the ant-cashew relationship and to explore the potential of ants replacing chemical pesticides in insect control. Using for-profit, commercial-size plantations as examples, we present information that cashew has a strong potential for arthropod-dependent protection from pests and suggest important habitat considerations for encouraging ants within cashew plantings.     

Ecology of an Improbable Association: The Pseudomyrmecine Plant‐ant Tetraponera tessmanni and the Myrmecophytic Liana Vitex thyrsiflora (Lamiaceae) in Cameroon1

In young individuals of the obligate myrmecophytic liana Vitex thyrsiflora, several species of ants and other arthropods compete for resources offered by the plant. In mature individuals, the only inhabitant is the ant species Tetraponera tessmanni, which is completely restricted to Vitex lianas as its sole host. Established colonies of this ant provide effective defense against herbivores. The association between V. thyrsiflora and T. tessmanni is unusual in two respects. First, the climbing life form is rare among myrmecophytes. Secondly, it is surprising that a pseudomyrmecine should be the obligate associate of a liana. Pseudomyrmecine plant‐ants often prune vegetation contacting their host plant. This behavior functions in part to protect against invasion of the host by ecologically dominant ants. In contrast, T. tessmanni does not prune and is associated with a plant whose success, and thus that of its resident ant colony, depends on contacts with many other plants. Several traits of V. thyrsiflora and T. tessmanni combine to make the colonization of host plants by potential competitors very difficult. These include behavioral and morphological filters restricting entrance into the plant and exploitation of the resources it can supply; plant anatomical organization that enables T. tessmanni workers to carry out all activities, except leaf patrolling, within a single, branched private nesting space within which all food resources offered by the plant are produced; and polygyny, permitting the colony to monopolize a large, rapidly growing and long‐lived territory.     

Low Density of Ant Lion Larva (Myrmeleon crudelis) in Ant‐Acacia Clearings: High Predation Risk or Inadequate Substrate?1

We experimentally determined whether the low density of antlion larvae found in ant‐acacia clearings is due to high levels of ant predation or an inadequate substrate for pit‐trap construction. Pit establishment was more affected by soil improvement than by the exclusion of ants, suggesting that soil condition is the main factor that affect antlions’density. The low density of this ant‐predator in ant‐acacia clearings may be considered as an indirect advantage of the ant's pruning behavior.     

Regulation of Brood-Care Behavior in the Dimorphic Castes of the Ant Pheidole morrisi (Hymenoptera: Formicidae): Effects of Caste Ratio, Colony Size, and Colony Needs

This study examines the social stimuli that regulate brood-care behavior in the two physical castes of the ant Pheidole morrisi. By increasing the proportion of major workers in a colony, brood-care behavior could be induced in individuals of this caste, which do not normally care for brood. Minor and major worker brood-care rates increased with the proportion of majors in the colony or as the need for brood care increased. Changes in colony size did not significantly affect the rate of either minor or major brood care. Major workers began to care for brood when the caste ratio reached a critical threshold but did not appear to be as efficient at rearing larvae as minor workers, which normally perform this task. After a perturbation that skewed the caste ratio toward majors, minor workers increased their rate of brood care, apparently to compensate for the inefficiency of brood care provided by majors. These results suggest that caste plasticity involves a social mechanism of ldquo;coupled compensation that maintains the efficiency of labor by ensuring that tasks are completed.     

Resource Assessment, Recruitment Behavior, and Organization of Cooperative Prey Retrieval in the Ant Formica schaufussi (Hymenoptera: Formicidae)

Foragers of the ant Formica schaufussi recruit nestmates to large anthropod prey and cooperatively transport the prey to the nest. The size of the group of ants retrieving prey is significantly correlated with the prey mass at the point at which the retrieval group reaches the nest entrance. To understand the mechanism involved in this size matching process, the regulation of retrieval group size was investigated by examining the modulatory role of trail pheromones in recruitment communication and the behavioral processes that might adjust retrieval group size to prey mass. Laboratory studies of hindgut, poison, and Dufour's gland extracts showed that the contents of the hindgut, which was determined to be the source of trail pheromone, induced recruitment and orientation behavior in ants and regulated the recruitment response of ants in the absence of any other communication signal. However, chemical mass communication alone did not appear to explain the regulation of retrieval group size. Scout ants assess whether to collect prey individually or recruit nestmates to group-retrieve 100-, 200-, or 400-mg prey but did not vary group size in relation to either the prey mass or the presence of interspecific competitors once the decision to initiate group retrieval was made. The number of recruits leaving the nest was independent of these factors and first matched prey mass during prey transport, possibly through a process of differential individual response to immobile versus mobile prey items. Unpredictable factors such as prey resistance to movement and rapidly changing degrees of interspecific competition may preclude scouts from fine-tuning the retrieval group size before it reaches the prey.     

Ecology and behavior of the seed-eating ponerine antBrachyponera senaarensis (Mayr)

Summary Colonies ofBrachyponera senaarensis, a species known for its adaptation to dry tropical conditions in Sudanes savannas, can also flourish in a wet tropical environment if it is particularly sunny and well-drained, e. g. in sandy regions. The feeding strategy of this species is opportunistic, with great flexibility of nesting, foraging, and diet according to the nature of the environmental constraints. Swarming takes place at the height of the rainy season. Foundation is partially claustral and haplometrotic or, more rarely, pleometrotic. Daily foraging activity of workers, which is mainly diurnal, peaks between 0700 h and 0900 h and then ceases between 1100 h and 1400 h. The size of workers varies between colonies, depending on the richness of their environment. Moreover, two worker subcastes may be distinguished in a colony: (1) individuals which are nonpigmented at birth and represent the majority of the worker population; and (2) larger workers, whose level of maturation is more advanced both morphologically and behaviorally, as shown by an age-polyethism study.     

The influence of queens of the antParatrechina flavipes on daughter and non-daughter workers, for the suppression of sexual production

The influence that the queen ofParatrechina flavipes (Smith) (Hymenoptera: Formicidae) has upon workers was investigated in field and laboratory nests. There was no significant difference in sexual production, either of gynes or males, between field queenright and queenless nests of the ant. A replicated laboratory experiment revealed that workers lay fewer eggs and rear fewer sexual larvae in the presence of their mother queen, while this reduction is not observed in workers with influence of non-mother queens. The results seem to support the queen's signal hypothesis by Keller & Nonacs (1993). The contradiction is explained by workers rearing sexuals in queenless satellite nests. There exists a probably complex regulation of the transfer of larvae between satellite and mother nests.