Dyed baits distribution in nests of Atta sexdens L. (Hym., Formicidae)

Dyed baits distribution in colonies of Atta sexdens was studied so as to test the hypothesis of uniform distribution. Three medium- to large-size (34–90 m²) colonies were used for the experiment; coloured dyed baits material was made available at the foraging orifices, which had previously been mapped out and grouped into three hypothetical sectors. After 24 h the colonies were killed and the nests excavated; the fungus was removed from each of the chambers for observation of the presence or absence of dyed baits. It was shown that coloured material from each of the different sectors was found in all the fungus chambers, thus confirming the hypothesis.     

Toxic effects of Canavalia ensiformis L. (Leguminosae) on laboratory colonies of Atta sexdens L. (Hym., Formicidae)

Laboratory colonies of the leaf-cutting ants Atta sexdens that were fed daily with leaves of Canavalia ensiformis showed a high ant mortality, and a significant decrease in fungal garden volume, with complete depletion of nests after 11 weeks of treatment.     

The sexspiaosa-group of the ant genus Polyrhachis F. Smith (Hym. Formicidae)

The sexspinosa-group of Polyrhachis is revised. Twelve species are recognised, two of which are described as new. Sixteen synonyms are recognised, mostly of infra-specific taxa. A key to the species and diagnostic notes of each species are included.     

The effect of the number of queens of the antLasius flavus (Fab.) (Hym., Formicidae) on their survival and on the rate of development of the first brood

Summary Populous colonies ofLasius flavus F. are generally haplometrotic, yet not infrequently several queens combine in founding nests. This aggregation after flight is not always accidental, but may arise from cooperation between the females in the digging of new burrows. Probably the queens become habituated to one another at this stage. In the laboratory the multi-female colonies were at an advantage over the single female ones, as the mortality of the queens was reduced and the first brood of workers was reared more rapidly. Grouping of the queens ofL. flavus and of those ofL. niger did not appear to influence the ovarial development of the survivors, and they all contributed to the establishment and the rearing of the first brood. This pleometrosis was temporary and the multi-queen colonies began to split into smaller units at the time of the appearance of the earliest pupae. InL. niger, fighting to death between the queens, at times of repeated ovipositions, also contributed towards the final state of haplometrosis.

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Résumé En général, les nids populeux deLasius flavus F. montrent de l'haplométrose, mais, quelquefois, plusieurs reines s'unissent pour fonder des nids. Ce rassemblement après le vol n'est pas toujours fortuit; il peut résulter de la coopération entre les reines pendant les excavations de nouveaux trous dans la terre. Il est probable qu'à ce moment les reines s'habituent les unes aux autres. Au laboratoire les colonies avec plusieurs reines étaient plus favorisées, car leur mortalité était assez réduite et les premières ouvrières furent produites plus rapidement que dans les nids à reines solitaires. Les ovaires des reines deL. flavus et deL. niger rassemblées en groupes, restèrent fonctionnels, et toutes les reines qui survécurent contribuèrent à l'établissement et à la nourriture de la première couvée. Cette pléométrose était temporaire et les colonies avec plusieurs reines commencèrent à se diviser à l'instant où parurent les premiers cocons. Plusieurs reines deL. niger s'engagèrent en combat jusqu'à la mort au moment des pontes, ce qui contribua également à l'état d'haplométrose.

     

Interspecific competition between Diadegma semiclausum Hellen (Hym., Ichneumonidae) and Cotesia plutellae (Kurdjumov) (Hym., Braconidae) in parasitizing Plutella xylostella (L.) (Lep., Plutellidea)

Abstract:  Interspecific competition between Diadegma semiclausum and Cotesia plutellae was investigated at 25°C in the laboratory, by exposing the third instar larvae of the diamondback moth, Plutella xylostella to both species together, either species alone or by exposing the host larvae already parasitized by one species, at different intervals, to the other. When host larvae were exposed simultaneously to two species in one arena, parasitism rates of the host by each species were not reduced by the presence of the other species; joint parasitism rate by two species was not significantly higher than that by either parasitoid alone. Both parasitoids could lay eggs into the host larvae which had previously been parasitized by the other species, leading to the occurrence of multiparasitized hosts. When host larvae were parasitized first by D. semiclausum and then being followed within 1–2 h by exposing to C. plutellae , or vice versa, ensuing parasitoid cocoons from the multiparasitized host larvae were nearly all C. plutellae . When host larvae were parasitized initially by C. plutellae and then being followed by D. semiclausum two or more days later, all parasitoids ensued from the multiparasitized hosts were C. plutellae . In contrast, when host larvae were parasitized initially by D. semiclausum and then being followed by C. plutellae two or more days later, most host larvae could not survive to prepupae and most of the ensuing parasitoid adults from the surviving hosts were D. semiclausum . Dissections of host larvae at various time intervals after parasitization by the two parasitoids showed that development of both parasitoids in multiparasitized hosts were somewhat arrested, and that the first instar larvae of C. plutellae could initiate a physical attack on the larvae of D. semiclausum and remove the latter.     

Der Kartonnestbau bei Lasius fuliginosus Latr. (Hym. Formicidae)

Zusammenfassung Lasius fuliginosus besiedelt hohle Baumstämme, die sie mit einem kartonartigen Material unterkammert. Der Karton besteht aus Holz — bisweilen auch aus Erdteilen und ist von einem Pilzmycel (Cladosporium myrmecophilum) durchwachsen. Die dünnschichtchromatographische Analyse ergab, daß nicht, wie bisher angenommen, das Mandibeldrüsensekret zum Kartonbau verwendet wird. Statt dessen wird, wie chromatographische Untersuchungen und Tracerversuche zeigten, mit eingeschlepptem Honigtau bzw. an die Ameisen verfüttertem Zuckerwasser das Kartonmaterial verklebt. Das Zuckerwasser stellt gleichzeitig das Nährmedium für den Nestpilz dar. Der Karton wird in Arbeitsteilung errichtet, wobei man 3 Arbeitergruppen unterscheiden kann: Bautiere, Festmaterialträger und Honigsammler.

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Carton-nest construction by Lasius fuliginosus Latr. (Hym. Formicidae)

Summary Lasius fuliginosus nests in hollow trees which it divides into chambers by building thin walls. The material used, usually wood but occasionally soil particles, is intermixed and overgrown by fungus mycelium (Cladosporium myrmecophilum). It was shown by thin-layer chromatography that, contrary to current opinion, the secretion of mandibular glands is not part of the building material. Tracer experiments as well as chromatography demonstrated convincingly that collected honey-dew as well as supplied sugar-water were used as a glue. This glue not only held the wood and soil particles together but also provided a culture medium for the fungus. During the construction of the nest chambers three type of workers cooperated: builders, carriers of solid material, and honey-dew-collectors.

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Mit Unterstützung der Deutschen Forschungsgemeinschaft.

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Herrn Prof. Lindauer danken wir für die Durchsicht des Manuskripts, Frl. H. Engel und Frau D. zu Sayn Wittgenstein für technische Hilfe.     

Effects of leaves of Ipomoea batatas (Convolvulaceae) on nest development and on respiratory metabolism of leaf-cutting ants Atta sexdens L. (Hym., Formicidae)

Abstract: Laboratory colonies of the leaf-cutting ants Atta sexdens feed daily with leaves of Ipomoea batatas s howed ant mortality and a significant decrease in the size of the fungal garden after the second week, with complete depletion of nests after 5 weeks of treatment. The mean oxygen consumption rate of these ants was higher than the control (ants collected from nests feed with leaves of Eucalyptus alba ), suggesting a physiological action of the leaves of I. batatas on the ants in addition to the effect of inhibiting the growth of the fungal garden.