Electrical signals during nectar sucking in the carpenter ant Camponotus mus

Ants of the same size can vary their intake rate of a given sucrose solution depending on the colony's needs for carbohydrates. As this capacity has not yet been described for another insect, the question of how they can do that was the focus of our work. When viscosity and ant-morphometry remain constant, changes in intake rate can only be attributed to the sucking forces. The aim of this study was to analyze the nectar sucking activity in the ant Camponotus mus. Feeding behavior seems to be under motivational control; therefore, we developed a non-invasive experimental device. We recorded the electrical signal generated during nectar feeding by offering ants sucrose solutions of different concentrations (from 10%w/w to 70%w/w). The signal frequency was between 2 and 12 peaks/s. We could distinguish two different patterns of electrical signal during feeding depending on the solution concentration. Only the more concentrated solutions reached frequencies higher than 7 peaks/s and the signal performance was quite irregular. For the other concentrations (10%, 30% and 50%), signal frequencies were lower than 6 peaks/s and the signal pattern was sinusoidal, regular and decreased with intake in all cases. We discuss the possible implications of these two signal patterns.     

Serotonin depresses feeding behaviour in ants

Feeding behaviour is a complex functional system that relies on external signals and the physiological state of the animal. This is also the case in ants as they vary their feeding behaviour according to food characteristics, environmental conditions and - as they are social insects - to the colony's requirements. The biogenic amine serotonin (5-HT) was shown to be involved in the control and modulation of many actions and processes related to feeding in both vertebrates and invertebrates. In this study, we investigated whether 5-HT affects nectar feeding in ants by analysing its effect on the sucking-pump activity. Furthermore, we studied 5-HT association with tissues and neuronal ganglia involved in feeding regulation. Our results show that 5-HT promotes a dose-dependent depression of sucrose feeding in Camponotus mus ants. Orally administered 5-HT diminished the intake rate by mainly decreasing the volume of solution taken per pump contraction, without modifying the sucrose acceptance threshold. Immunohistochemical studies all along the alimentary canal revealed 5-HT-like immunoreactive processes on the foregut (oesophagus, crop and proventriculus), while the midgut and hindgut lacked 5-HT innervation. Although the frontal and suboesophageal ganglia contained 5-HT immunoreactive cell bodies, serotonergic innervation in the sucking-pump muscles was absent. The results are discussed in the frame of a role of 5-HT in feeding control in ants.     

Relation between termite numbers and the size of their mounds

This article provides a meta-analysis of quantitative data available in literature regarding the relation between termite numbers and the volume of their mounds for 24 species belonging to 13 genera. The leading question behind this analysis is: “how do the respiratory gas exchanges regulate the size of termite mounds?” This question is answered through the analysis of the log–log regression between the volume of the mound and the number of inhabitants. The most confident data support the hypothesis of a respiratory regulation that can be achieved through a relation between the termite numbers and (1) the volume of their mounds (slope of the regression near 1, Noditermes), (2) the surface of the outer walls of their mounds (slope of the regression near 0.67, Termitinae and Nasutitermes) or (3) a compromise between the surface of the outer walls of their mounds and some linear structures of their nests (slope of the regression between 0.67 and 0.33, Trinervitermes and Macrotermes). The way this is achieved is linked with the architecture of the mound. A confident relation was found between the number of individuals and the epigeal volume of their mounds for 18 species for which the most reliable data were provided. Three more accurate models are proposed for estimating the termite population based on the nest material and architecture and on the size of the termites.     

Nectar feeding and body size in the ant Camponotus mus

Summary: Feeding behavior and worker polymorphism were studied in the ant Camponotus mus. Individual workers were conditioned to visit an arena in which an ad libitum food source of 60% (w/w) sucrose solution was offered. Individual feeding time, crop load, and intake rate were recorded. Worker head width and pronotum width were measured. Behavioral and morphometric variables were analyzed in relation to ant weight. C. mus workers of the laboratory nest have an elemental polymorphism with monophasic allometric growth. Worker size affected feeding dynamics. Load weight and intake rate were positively correlated with ant weight, whereas feeding time was independent of ant weight. Size related differences in intake rate could not be attributed to differences in pumping frequency, and could be attributed to differences in the volume ingested per pumping cycle.     

Variations thermiques dans les nids deTrinervitermes geminatus Wasmann,en relation avec le milieu extérieur dans la savane de Lamto (Côte d'Ivoire)

Résumé Des enregistrements de températures ont été effectués dans des termitières deTrinervitermes geminatus Wasmann et dans le sol en juin 1968, puis en janvier 1969, avant, pendant et après le passage des feux de brousse.Les termitières deTrinervitermes geminatus Wasmann, partiellement épigées, sont soumises à de fortes variations de température en surface, en relation avec l'éclairement et les pluies. De même que dans le sol, ces variations se propagent lentement dans la termitière et s'atténuent avec la profondeur: leur amplitude passe de 40° C environ au sommet de la termitière à 2 ou 3° C dans les loges souterraines, amplitude également observée dans le sol à profondeur équivalente.Sans que l'on puisse parler de régulation thermique de la part des termites, il existe néanmoins une relation entre la température au centre du nid et la taille de ce nid: l'amplitude thermique journalière des nids de grande taille étant nettement plus faible que celle des petits nids. Ceci ne résulte probablement que de l'inertie thermique qui est plus importante dans les grandes termitières.L'influence immédiate du passage des feux de brousse se révèle négligeable: elle ne se manifeste qu'en surface de la partie épigée du nid.

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Summary Temperature measurements have been made in mounds ofTrinervitermes geminatus Wasmann as well as in the soil. They have been recorded in june 1968 and in january 1969, before, during and after the bush fire.The temperature of the mounds varies with the conditions of enlightment and rain. At the top of the nests, the variations are about 40° C (72° F); in the subterranean rooms, they are about 2, 5° C (4, 5° F), just as in the soil at equal depth.The variation of temperature is smaller in bigger mounds but there is probably no regulation by the termites themselves. Only the mass of the mound seems to intervene in the deadening of the external variations of temperature.The immediate influence of the bush fire is insignificant: only the surface of the mound offers a very momentary variation.

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Zusammenfassung Temperaturmessungen sind während der Monate Juni 1968 und Januar 1969 (vor, während und nach der Buschfeuer) in den Termithügel vonTrinervitermes geminatus Wasmann sowie in dem Boden vorgenommen worden.Die Temperatur des Nestes wird durch Licht und Regenbedingungen beeinflusst. Die Temperatur ändert sich ungefähr um 40° C in der Spitze des Nestes, während sie um 2–3° C in den unterirdischen Logen schwankt, ebenso wie die Temperatur im Boden in gleicher Tiefe.Die Temperaturschwankungen sind kleiner in grösseren Nesten. Die Temperaturregelung seitens der Termiten ist wahrscheinlich ausgeschlossen: nur die Masse des Nestes scheint die Dämpfung der Temperaturschwankung zu bedingen.Der Einfluss des Buschfeuers ist nicht besonders: nur die Oberfläche des Hügels zeigt eine momentane Temperaturschwankung.

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Aspirant au Fonds National Belge de la Recherche Scientifique.

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La présente étude entre dans le cadre des recherches poursuivies à la Station d'Ecologie tropicale de Lamto (B. P. 28, N'Douci (Rép. de Côte d'Ivoire), installée par l'E.N.S., avec l'aide du C.N.R.S. (R.C.P. n^o 60), dans le but d'analyser la structure et la vie d'une biocénose terrestre.     

Efficient Egress of Escaping Ants Stressed with Temperature

In the present work we investigate the egress times of a group of Argentine ants (Linepithema humile) stressed with different heating speeds. We found that the higher the temperature ramp is, the faster ants evacuate showing, in this sense, a group-efficient evacuation strategy. It is important to note that even when the life of ants was in danger, jamming and clogging was not observed near the exit, in accordance with other experiments reported in the literature using citronella as aversive stimuli. Because of this clear difference between ants and humans, we recommend the use of some other animal models for studying competitive egress dynamics as a more accurate approach to understanding competitive egress in human systems.     

Impact of three aquatic invasive species on native plants and macroinvertebrates in temperate ponds

Biological plant invasions pose a serious threat to native biodiversity and have received much attention, especially in terrestrial habitats. In freshwater ecosystems impacts of invasive plant species are less studied. We hypothesized an impact on organisms from the water column and from the sediment. We then assessed the impact of three aquatic invasive species on the plants and macroinvertebrates: Hydrocotyle ranunculoides, Ludwigia grandiflora and Myriophyllum aquaticum. Our research on 32 ponds in Belgium indicated that the reduction in the native plant species richness was a common pattern to invasion. However, the magnitude of impacts were species specific. A strong negative relationship to invasive species cover was found, with submerged vegetation the most vulnerable to the invasion. Invertebrate richness, diversity and abundance were measured in sediments of invaded and uninvaded ponds along a gradient of H. ranunculoides, L. grandiflora, and M. aquaticum species cover. We found a strong negative relationship between invasive species cover and invertebrate abundance, probably due to unsuitable conditions of the detritus for invertebrate colonization. Taxonomic compositions of aquatic invertebrate assemblages in invaded ponds differed from uninvaded ponds. Sensitive benthos, such as mayflies were completely absent in invaded ponds. The introduction of H. ranunculoides, L. grandiflora, and M. aquaticum in Belgian ponds has caused significant ecological alterations in the aquatic vegetation and the detritus community of ponds.     

Growth and demography ofCubitermes speciosus mounds (Isoptera,Termitidae)

The growth and demography ofCubitermes speciosus mounds were studied in an equatorial forest ecosystem near Kisangani, Zaïre. The mounds were censused and measured on eight occasions from June 1985 to January 1993 on 25 plots of 100 m².Mounds were found to grow in two ways: either they were enlarged sporadically, leading to a correlation between age and size; or they were no longer enlarged after a 2-year period of initial growth, which means that both large and small mounds can be old.The number of living mounds was fairly constant: it varied between 112 and 152 ha^–1 with an average of 139 ha^–1, and about a quarter of them were renewed each year. However, a clear tendency was observed over our 7.5-year observation period: the average size of the mounds increased regularly and was 2.7 times larger in 1993 than in 1985.Monthly birth and death rates were estimated using a model of continuous growth. Life expectancy at the age of 3 months was estimated from a survivorship curve at 3.5 years.     

Nectar feeding by the hovering hawk moth Macroglossum stellatarum: intake rate as a function of viscosity and concentration of sucrose solutions

Although nectar feeding in insects has long been studied, the knowledge of the effect of nectar energy content on the ingestion dynamics separately from the viscosity of the fluid is very limited. To determine the effects of both factors on the feeding behavior of the hovering hawk moth Macroglossum stellatarum, we developed a method to independently manipulate sucrose concentrations and viscosity. The intake rate was analyzed as a function of sucrose concentration, the concentration at constant viscosity (kept constant by adding tylose, an inert polysaccharide), and of the different viscosities of a 30% weight/weight (w/w) sucrose solution (by adding different amounts of tylose). By increasing the concentration, and thus its viscosity, the solution intake rate (in microl s (-1)) decreased beyond a 20% w/w sucrose solution. For a 30% sucrose solution, the intake rate decreased with increasing viscosity. At constant viscosity, the solution intake rate decreased beyond a 30% w/w sucrose solution. However, if we considered the quantity of sucrose ingested per unit time (sucrose intake rate), the same fitted maximum was attained for both series in which the sucrose concentration changed (33.6% w/w). Results suggest that the gustatory input affects the dynamics of fluid ingestion separately from the viscosity.