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Non-aggressive behavior in the large soldier ofNasutitermes exitiosus (Hill) (Isoptera: Termitidae)

Fehlen agressiven Verhaltens grosser soldaten von Nasutitermes exitiosus

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Summary

Colonies ofNasutitermes exitiosus (Hill) near Canberra, Australia were studied during 1972. In addition to the reproductive pair, instars of the large and the small worker lines, and the typical nasutiform soldier, each mound examined also contained at least a few soldiers (first mentioned byHill in 1946) which were not of the usual type. They were larger, had shortened, downwardly deflected rostrums, and were derived from the large instead of from the small worker line. Although both the small soldiers (SS) and the large soldiers (LS) produced and expelled a terpenoid secretion from the cephalic gland, field and laboratory studies showed that they differed markedly in their behavior.

In field tests when holes were punched in a mound surface the defending soldiers that congregated at the breach rarely included LS's. This was true even for an aberrant mound in which the LS's comprised over 80 % of the total soldier population. On the other hand, LS's were found in considerably larger numbers in foraging parties (12.4 % of the foraging soldiers, as compared with <2 % of the total soldiers composing a colony). The function of LS's in foraging, however, was not aggressively defensive. When pieces of wood containing foragers were isolated from the soil and tapped, less than 2 % of the soldiers that emerged (exhibiting defensive behavior) were LS's. About 56 % of the soldiers that secreted themselves within the wood and had to be extracted were LS's. Their behavior was like that of the foraging workers.

Laboratory tests gave similar results. Tapping and other disturbances at an exit hole in a small wooden chamber containing equal numbers of workers, LS's, and SS's caused emergence (and in defensive stance) of SS's only. Disturbance of foragers in a laboratory colony caused workers and LS's to retreat precipitously into the sheltering container, while SS's remained «on guard».

The advantage to the colony of the presence of these non-combative soldiers is not clear, but their enhanced numbers in foraging parties implies a usefulness, at least in this important activity.

Zusammenfassung

Während des Jahres 1972 wurden Kolonien vonNasutitermes exitiosus (Hill) in der Nähe von Canberra, Australien, beobachtet. Dabei fanden sich in jedem untersuchten Hügel neben dem Geschlechtstierpaar, allen Stadien grosser und kleiner Arbeiter und den üblichen Nasuti-Soldaten stets auch einige Soldaten von nicht «normalem» Typ, wie sie zum ersten Mal vonHill 1946 erwähnt wurden. «Normale» Soldaten sind klein und leiten sich von kleinen Arbeitern ab; «abnormale» sind grösser, tragen verkürzte, nach unten gerichtete Rostren und stammen von grossen Arbeitern. Beobachtungen im Feld und im Labor zeigten bemerkenswert verschiedenes Verhalten der kleinen (SS) und der grossen (LS) Soldaten.

Wenn im Feld Löcher in eine Nestoberfläche geschlagen wurden, fanden sich unter den zur Verteidigung zusammenlaufenden Soldaten nur selten LS. Dies galt sogar für ein aberrantes Nest, in dem die LS mehr als 80 % der Soldaten-Population ausmachten. Andrerseits fanden sich LS in weitaus grösserer Anzahl in nahrungssuchenden Gruppen (12.4 % der nahrungssuchenden Soldaten gegenüber weniger als 2 % der Soldaten der gesamten Kolonie). Die Funktion der LS bei der Nahrungssuche war jedoch nicht die aktiver Verteidigung. Wenn man nämlich Holzstücke, die solche Gruppen enthielten, aufnahm und abklopfte, waren nur weniger als 2 % der hervorkommenden (und Verteidigungsverhalten zeigenden) Soldaten LS; etwa 56 % der im Holz verborgenbleibenden Soldaten — die herausgeholt werden mussten — waren hingegen LS. Ihr Verhalten glich dem der nahrungssuchenden Arbeiter.

Laborversuche brachten ähnliche Ergebnisse: Klopfen und andere Störungen am Ausgang einer kleinen Holzkammer, die die gleiche Anzahl Arbeiter, LS und SS enthielt, veranlassten nur SS zum Herauskommen in Verteidigungsstellung. Bei Störung der Nahrungssucher einer Laborkolonie zogen sich Arbeiter und LS eilig in den schützenden Behälter zurück, während die SS «auf Wache bleiben».

Der Vorteil dieser grossen Soldaten für eine Kolonie ist nicht klar ersichtlich. Ihre erhöhte Anzahl bei nahrungssuchenden Gruppen lässt jedoch — jedenfalls für diese wichtige Tätigkeit — einen solchen möglich erscheinen.

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McMahan, E.A. Non-aggressive behavior in the large soldier ofNasutitermes exitiosus (Hill) (Isoptera: Termitidae). Ins. Soc 21, 95–106 (1974). https://doi.org/10.1007/BF02222982

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