Titre : | Some experiments concerning thermal adjustment and respiratory metabolism in insects |
Auteurs : | Agrell, Ivar |
Type de document : | article/chapitre/communication |
Année de publication : | 1947 |
Format : | 48 p. |
Langues: | = Anglais |
Mots-clés: | ABEILLE ; BEE |
Résumé : |
The aim of the investigation is to make a contribution to the problem in what degree the thermal reaction of the respiratory metabolism in insects is qualitatively or quantitatively changed when subjected experimentally for some length of time to variations in the thermal environment. The material under investigation consists of imagines of Stauroderus bicolor CHARP. (Orthoptera), Formica rufa L. (Hymenoptera), Stomoxys calcitrans L. (Diptera), Forficula auricularia L. (Dermaptera), larvae of Ephestia kühniella Z. (Lepidoptera) and Byrrhus pilula L. (Coleoptera), as well as pupae of Phalera bucephala L. (Lepidoptera). The test groups of the different species examined are transferred from an originally uniform environment, i.e. the same limited habitat to three different thermal enviromnents, + 5°C, + 30°C and c:a + 18°C. At more or less regular intervals test animals were taken from these groups and their oxygen consumption and carbon dioxide production were determined at + 18°C. The respiratory exchange at + 18°C is thus used as an index of eventual metabolic changes caused by the change in the thermal environment. The measurements are made with the Thunberg-microrespirometer. In a few cases the respiratory measurements have been supplemented by investigation of the possible change in the resistance to cold. The results of the various experiments are discussed in two parts, Discussion I, dealing with insects, which during the experimental period were not changed by a metamorphosis, and Discussion II, dealing with the pupae of Phalera bucephala, which more or less undergo a metamorphosis independently of the temperature. A theoretical survey is made in Discussion I of various possibilities of a change in the potential respiration due to a changed environmental temperature. On this basis the separate experimental results are then discussed. All the test animals show a quantitatively or qualitatively changed gas metabolism caused by the previous environmental temperature. In Stauroderus bicolor the respiratory rate decreases more and more rapidly the higher the environmental temperature. This is assumed to be an effect of fasting. The other test animals show either a decrease in the potential respiration measured at + 18° C, which sets in rapidly for both heat and cold influence (Forficula auricularia and Ephestia kiihniella), or a more or less gradual increase in the potential respiration both through the influence of high and lowered environmental temperature (Formica rufa, Stomoxys calcitrans and Byrrhus pilula). Several possible explanations are discussed: compensatory adjustment of the metabolism to the environmental temperature, systematically altered temperature coefficient, remaining thermal effect, or reduction in vitality. In connexion with the increased respiratory quotient, which occurs at high temperature is discussed the existence of eventual anoxybiotic processes. A systematic change in RQ in Byrrhus pilula is assumed to be organically connected with its hibernation. Discussion II deals with the results of the experiments with the hibernating pupae of Phalera bucephali. The respiratory quantity and quality are chiefly affected by the developmental state of the pupae but can be altered by the effect of a different thermal environment. During the development the pupae have a period of minimal metabolism which is characterized by an extremely low RQ, below 0.1. If the pupae are kept constantly at + 18 ° C and so the normal decrease in temperature at the coming of winter fails to take place, a diapause is induced with low respiratory intensity and a constantly low RQ. A fall of temperature to + 5 ° C, on the other hand, increases the developmental ability; a latent development sets in; the rate of the potential respiration increases gradually, mainly due to increased thermal sensibility, and the RQ becomes stabilized at a constant and higher value. Finally, if the pupae are returned to higher environmental temperature, + 18' C, a strong respiratory increase occurs and. the RQ attains a still higher constant value, a subitan development commences, and the pupae emerge before long. An extremely high environmental temperature, + 30 ° C seems to some degree to be able to break the diapause in the same way as a low one. In combination with the various developmental phases of the pupae, those metabolic processes are discussed, which are likely to cause the low RQ, and reasons are submitted for an assumption of two simultaneous metabolic types, one conversion of fat into carbohydrate and the other a complete combustion of the latter substance. With rising state of development, the pupae change from conversion type of metabolism to combustion type.
The experiments are supplemented by an investigation of the dependence of respiration on temperature with progressive pupal development. A decrease in the RQ has been observed with rising temperature. The relationship between conversion and combustion processes are discussed in this connexion. The actual loss in water is calculated for various test groups of pupae from the combination of the gas exchange and the loss in weight, and it seems mainly to depend on the environmental temperature and not on the magnitude of the metabolism. There is a thermal optimum for the cost of production of the imago. |
Source : | Arkiv for Zoologi, vol.39A, n°10, 48p. |
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