Sperm transfer during mating in the pharaoh's ant, Monomorium pharaonis

Abstract.  Sperm transfer in the pharaoh's ant Monomorium pharaonis (L.) is studied by making longitudinal sections through the gasters of mating pairs fixed in copula. Sperm is transferred inside a spermatophore similar to those found in two other ants, Diacamma sp. from Japan and Carebara vidua . Sharp teeth-ridges are present on the penis valves and, during copulation, these teeth make contact with a thick and soft cuticular layer covering the bursa copulatrix. This ensures an attachment long enough for the successful transfer of the spermatophore to the right position inside the female oviduct. The thick cuticle also protects the queen from serious damage by the male's sharp claspers. After a first successful copulation, sperm is still present inside the male's seminal vesicles, suggesting that males can mate multiply. Additional experiments, where single, initially virgin males are presented to several virgin females, confirm this.     

Pheromone trail decay rates on different substrates in the Pharaoh's ant, Monomorium pharaonis

Abstract. Many ants use pheromone trails to organize collective foraging. This study investigated the rate at which a well‐established Pharaoh's ant, Monomorium pharaonis (L.), trail breaks down on two substrates (polycarbonate plastic, newspaper). Workers were allowed to feed on sucrose solution from a feeder 30 cm from the nest. Between the nest and the feeder, the trail had a Y‐shaped bifurcation. Initially, while recruiting to and exploiting the feeder, workers could only deposit pheromone on the branch leading to the feeder. Once the trail was established (by approximately 60 ants per min for 20 min), the ants were not allowed to reinforce the trail and were given a choice between the marked and unmarked branches. The numbers of ants choosing each branch were counted for 30 min. Initially, most went to the side on which pheromone had been deposited (80% and 70% on the plastic and paper substrates, respectively). However, this decayed to 50% within 25 min for plastic and 8 min for paper. From these data, the half‐life times of the pheromone are estimated as approximately 9 min and 3 min on plastic and paper, respectively. The results show that, for M. pharaonis, trail decay is rapid and is affected strongly by trail substrate.     

Changes in food selection by workers of the pharaoh''s ant, Monomorium pharaonis

The results from simple choice test experiments with laboratory and field colonies of pharaoh's ants have revealed two behavioural traits that influence the way in which foraging worker ants respond to foods. Initially, worker ants from laboratory colonies showed a distinct preference for certain foods (e.g. honey and peanut butter). However, when given only these 'preferred' foods continuously for several weeks, workers showed a marked preference for other foods when offered a choice. This 'satiation' response occurred even though the initial diet was originally highly attractive to foraging workers. In addition, workers show a marked tendency to alternate between carbohydrate foods and protein foods. Thus, workers from colonies fed predominantly on proteins, subsequently showed a marked preference for carbohydrates, and vice versa. The 'satiation' and 'alternation' responses to foods ensure that colonies receive a diet that is both varied and balanced. In addition, these aspects of feeding behaviour have important consequences for the use of food-based baits in control measures against Monomorium pharaonis (L.).     

The dynamics of collective exploration and trail-formation in Monomorium pharaonis: experiments and model

Abstract. When exploring a chemically unmarked area devoid of food sources, workers of the pest ant Monomorium pharaonis L. (Formicidae, Myrmicinae) leave scent marks on the ground and after 30–60min a network of diverging exploratory trails begins to emerge.
Exploratory activity is affected by the nutritional state of the colony and a period of food deprivation induces a dramatic increase in the number of workers leaving the nest. A mathematical model based on a logistic growth equation is proposed to describe the exploratory recruitment observed. When travelling along exploratory trails the proportion of ants displaying trail-laying behaviour is higher for outbound than for nestbound workers. Outbound ants also show a greater propensity than nestbound ants to follow the scent marks of their nestmates. The chemical used to mark a novel area does not appear to be colony-specific and thus does not have a territorial function sensu stricto. The adaptive value of the collective exploratory behaviour observed in this study is discussed in relation to the common features of other pest ant species described in the literature.     

Regional and functional differentiation in the fat body of pharaoh's ant queens, Monomorium pharaonis (L.)

The insect fat body is generally described as a uniform tissue with multiple functions, but we have found evidence of cell differentiation in the Monomorium fat body. We show that the fat body of a mature egg-laying pharaoh's ant queen is a result of a preceding remodeling of cell material comprising at least 11 different fat cell types, located at specific positions in the head, alitrunk (thorax) and gaster (abdomen). The cell types are classified based on their position, histochemistry, ultrastructure, and immunoreactivity for vitellogenin/vitellin. Some of these cells are primordial cells present at emergence, others invade the histolysing flight muscle tissue, and still others disappear during the maturation process. Only one type, the subepidermal fat cell of the gaster, is active in vitellogenin synthesis and is the only cell type in close association with oenocytes. Although only this type produces vitellogenin, our material indicates that most fat cell types are essential to support egg production. In some queens vitellogenin was found to form crystals in ventral vitellogenin-producing fat cells. This indicates an imbalance between vitellogenin production in the fat cells and uptake in the oocytes, which is probably related to a cyclic regulation of egg production.     

Dominance Interactions Regulate Worker Mating in the Polygynous Ponerine Ant Gnamptogenys menadensis

In queenless ants, workers compete aggressively to be reproductives instead of sterile helpers. To limit the number of reproductives, either mating or egg-laying by mated workers can be regulated. In Gnamptogenys menadensis , all mated workers reproduce, and field data presented here indicate that mating is not random. We removed gamergates experimentally (n=16 groups) to induce mating and gamergate replacement. Virgin workers engaged in agonistic interactions, allowing us to classify them into two groups: dominants performed antennal boxing and biting, while subordinates did not. However, a few subordinates cooperated to immobilize individual dominant workers. This effectively reduced the number of dominants because immobilized dominants became subordinates. Six to 12 wks after the removal of reproductives, between one and eight dominants per colony started to perform 'sexual calling' outside the nest entrance. Sixteen (out of 33) dominants mated with foreign males introduced in five experimental groups. None of the subordinate workers mated. The probability of mating is thus regulated by dominance interactions among workers and immobilizations initiated by infertile workers in this polygynous queenless ant.     

Influence of larvae and workers on egg production of queens of the pharaoh's ant,Monomorium pharaonis (L.)

Summary Social regulation of egg production and weight in queens was studied in relation to presence and absence of larvae and workers in the pharaoh's ant,Monomorium pharaonis (L.).Results were obtained by counting eggs and weighing queens under various conditions.The results confirm the existence of a positive feed-back loop between mated queens and their larvae as evident from a correlation (Y = 4.575 * X + 6.452) between the number of large worker larvae (X) and the egg yield (Y). This correlation seems to relate to the queens preferential feeding on larval secretions. Queens without larvae maintained a low level of egg production of about 6 eggs/day. Queens deprived of larvae as well as workers stopped producing eggs within 24 hours.Repletes, special workers, with greatly distended gasters functioned as a buffer retarding decline of egg production by feeding the queens during short periods without larvae.     

Effectiveness of methoprene-impregnated baits in the control of Monomorium pharaonis ant populations infesting health establishment and households

The use of baits consisting of dried egg yolks and impregnated with 0.5% of methoprene, loosely applied twice within 8-12 days at the rate of 1 g of bait per 3-6 m2 of floor surface area at each application was found to result consequently in a complete eradication of M. pharaonis ant populations in two medium-size health establishments and in one apartment house. Under more favorable conditions in another health establishment the use of methoprene-impregnated baits applied twice at the average dose of 1 g per as many as 46 m2 floor area proved equally effective in ensuring permanent eradication of ants. Providing that all colonies on the premises can be affected by bait a complete eradication of ants can be expected within 100 days after the first application of bait.     

Behavioral and Chemical Correlates of Long-Term Queen Adoption in the Facultative Polygynous Ant Ectatomma tuberculatum

In ants, queen adoption is a common way of achieving secondary polygyny but the mechanisms involved are little known. Here we studied the process of long-term adoptions of alien queens in the facultative polygynous ant Ectatomma tuberculatum. In eight out of 10 successful adoption experiments, all the introduced queens showed similar behavior and fecundity as the resident queens even after 2 months, indicating complete integration into the colony. Chemical analysis revealed that the cuticular hydrocarbon profiles of resident and introduced queens were clearly distinct from those of workers and that they did not change after adoption. We propose that queen-specific cuticular hydrocarbon profile may represent a reliable signal of queen’s fertility and discuss about the evolution of high level of queen acceptance in E. tuberculatum.     

Caste regulation in the pharaoh's ant Monomorium pharaonis: recognition and cannibalism of sexual brood by workers

Abstract In colonies of the pharaoh's ant Monomorium pharaonis (L), new males and queens can be produced at any time by the removal of the inhibitory effect of the presence of existing fertile queens. When queens are absent, workers rear sexual larvae and will also accept sexual larvae introduced from other nests. However, in the presence of fertile queens workers cannibalize sexual brood, and will not accept male or queen larvae or pre-pupae from other nests, although worker brood is always accepted and reared. Worker larvae are covered in bifurcated hairs, whereas sexual larvae are essentially hairless. Workers may use these morphological cues to distinguish between sexual and worker brood stages.     

Sting,Carry and Stock: How Corpse Availability Can Regulate De-Centralized Task Allocation in a Ponerine Ant Colony

We develop a model to produce plausible patterns of task partitioning in the ponerine ant Ectatomma ruidum based on the availability of living prey and prey corpses. The model is based on the organizational capabilities of a “common stomach” through which the colony utilizes the availability of a natural (food) substance as a major communication channel to regulate the income and expenditure of the very same substance. This communication channel has also a central role in regulating task partitioning of collective hunting behavior in a supply&demand-driven manner. Our model shows that task partitioning of the collective hunting behavior in E. ruidum can be explained by regulation due to a common stomach system. The saturation of the common stomach provides accessible information to individual ants so that they can adjust their hunting behavior accordingly by engaging in or by abandoning from stinging or transporting tasks. The common stomach is able to establish and to keep stabilized an effective mix of workforce to exploit the prey population and to transport food into the nest. This system is also able to react to external perturbations in a de-centralized homeostatic way, such as to changes in the prey density or to accumulation of food in the nest. In case of stable conditions the system develops towards an equilibrium concerning colony size and prey density. Our model shows that organization of work through a common stomach system can allow Ectatomma ruidum to collectively forage for food in a robust, reactive and reliable way. The model is compared to previously published models that followed a different modeling approach. Based on our model analysis we also suggest a series of experiments for which our model gives plausible predictions. These predictions are used to formulate a set of testable hypotheses that should be investigated empirically in future experimentation.     

Morphology of a novel glandular epithelium lining the infrabuccal cavity in the ant Monomorium pharaonis (Hymenoptera, Formicidae)

A novel glandular epithelium lining the infrabuccal cavity and anterior pharynx is described in both workers and queens of the pharaoh's ant Monomorium pharaonis. The infrabuccal cavity, connected with the buccal tube, forms a ventral outgrowth of the anterior pharynx, and as such displays the tegumental lining with a cuticle and an epithelial layer. In its dorsal region, the cavity's epithelium reaches a thickness of approx. 11–12 μm in both workers and queens, which is considerably thicker than the epithelium lining the rest of the infrabuccal cavity. Also the possible role of the infrabuccal gland is discussed.     

Reproductive strategies of the exotic Pharaoh's ant,Monomorium pharaonis (L.) (Hymenoptera: Formicidae) in Brazil

Summary

The production of sexual forms in laboratory colonies of Monomorium pharaonis was followed over a 19-month period. Cycles of production occurred at intervals of 4 months, with male investment inversely proportional to the number of gynes produced. There was a tendency for colonies to produce only males or females as total sexual production increased. Sperm counts of known-aged males suggest that they mate twice, in contrast to European populations. Sex-ratio was heavily female-biased, contrary to predictions for polygynous ant species.     

Caste regulation in the pharaoh's ant Monomorium pharaonis: the influence of queens on the production of new sexual forms

ABSTRACT. In colonies of Monomorium pharaonis (L.), the presence of fertile queens normally prevents the production of new queens and males (sexuals). The inhibitory effect of the presence of fertile queens is not shared by virgin queens or by freshly killed dead queens, but can be substituted by the artificial introduction of eggs. Moreover, fertile queens made sterile by exposure to a Juvenile Hormone analogue lose their ability to prevent the rearing of new sexuals. Thus, the inhibitory action of queens is mediated via the eggs that they lay, such that the rearing of new sexuals is limited to the times when either the number or fecundity of extant queens is reduced. Workers appear able to detect changes in the number of eggs present in the colony. When eggs are plentiful (i.e. when queens are laying at maximum rates), only worker brood is reared, but if egg numbers decline, workers will respond by rearing a new batch of males and queens. This method of caste regulation is highly efficient, and the inhibitory action of eggs on the production of sexuals is comparable to the action of 'queen substances' reported in some other social insects.     

Functional morphology of the postpharyngeal gland of queens and workers of the ant Monomorium pharaonis (L.)

Eelen D., Børgesen L.W. and Billen J. 2006. Functional morphology of the postpharyngeal gland of queens and workers of the ant Monomorium pharaonis (L.). —Acta Zoologica (Stockholm) 87 : 101–111 The postpharyngeal gland (PPG) is unique to ants and is the largest exocrine gland in their head. In queens of the pharaoh's ant, Monomorium pharaonis, the gland contains approximately 15 finger‐like epithelial extensions on each side and opens dorsolaterally in the posterior pharynx. In these ants the PPG morphology varies considerably according to age and mating status. The epithelial thickness increases with age and reaches a maximum at 3 weeks in both virgin and mated queens. A considerable expansion of the lumen diameter occurs in both groups between 4 and 7 days. Virgin queens release their secretion into the gland lumen from an age of 7 days, whereas mated queens accumulate large amounts of secretion in their epithelium. The increasing epithelial thickness, together with the increasing lumen diameter, the presence of numerous inclusions in the epithelium and the release of secretion, are indicative for increasing gland activity. The gland ultrastructure indicates involvement in lipid metabolism and de novo synthesis of lipids. The PPG of workers consists of 12 finger‐like tubes at each side. There is a significant difference in epithelial thickness between nurses and repletes and between nurses and foragers. We suggest the PPG serves different purposes in pharaoh's ants: it is likely that the PPG of workers and virgin queens is used to feed larvae. In mated queens the gland probably plays a role in providing the queen with nutritious oils for egg production. The PPG may also function in signalling species nestmate and caste identity, as well as in the reproductive capacity of the queens.     

Coupled computational simulation and empirical research into the foraging system of Pharaoh's ant (Monomorium pharaonis)

The Pharaoh's ant (Monomorium pharaonis), a significant pest in many human environments, is phenomenally successful at locating and exploiting available food resources. Several pheromones are utilized in the self-organized foraging of this ant but most aspects of the overall system are poorly characterised. Agent-based modelling of ants as individual complex X-machines facilitates study of the mechanisms underlying the emergence of trails and aids understanding of the process. Conducting simultaneous modelling, and simulation, alongside empirical biological studies is shown to drive the research by formulating hypotheses that must be tested before the model can be verified and extended. Integration of newly characterised behavioural processes into the overall model will enable testing of general theories giving insight into division of labour within insect societies. This study aims to establish a new paradigm in computational modelling applicable to all types of multi-agent biological systems, from tissues to animal societies, as a powerful tool to accelerate basic research.     

香茅醛缩醛类化合物的合成及其对小黄家蚁的驱避活性

【目的】香茅醛类化合物具有较好的蚂蚁驱避活性,本研究旨在筛选具有良好驱避活性的新的萜类蚂蚁驱避剂。【方法】以香茅醛为原料合成了香茅醛二甲缩醛、香茅醛二乙缩醛、香茅醛二正丙缩醛、香茅醛二异丁缩醛、香茅醛乙二缩醛、香茅醛1,2-丙二缩醛和香茅醛1,3-丙二缩醛等化合物。所得产品经纯化后,用IR, MS, ¹H NMR及¹³C NMR进行结构表征,并在不同浓度下对小黄家蚁Monomorium pharaonis进行驱避活性测试。【结果】各化合物对小黄家蚁具有一定的驱避活性：在10 mg/mL的浓度下,除香茅醛二甲缩醛以外,其他化合物的驱避率均达到70%以上,其中香茅醛二乙缩醛、香茅醛乙二缩醛和香茅醛1,3-丙二缩醛对小黄家蚁的驱避率分别为87.47%,100%和97.53%。浓度为2.5 mg/mL时,其中5个化合物的驱避效果明显下降,但香茅醛乙二缩醛和香茅醛1,3-丙二缩醛仍然表现出很好的驱避活性,驱避率分别为85.33%和97.10%。方差分析也表明,香茅醛1,3-丙二缩醛在同一浓度下驱避效果最佳,其次是香茅醛乙二缩醛。【结论】结果说明,香茅醛二乙缩醛、香茅醛乙二缩醛和香茅醛1,3 丙二缩醛可以用作小黄家蚁驱避剂,而香茅醛乙二缩醛和香茅醛1,3-丙二缩醛可以达到更好的驱避效果,使用浓度为2.5 mg/mL即可。本研究为良好萜类蚂蚁驱避剂的筛选提供了参考依据。     

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.