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§ The smallest category of a zoocoenosis: the catena | 81 high abundance in arvideserta of corrumpent populations, can be partially attributed to this lack of intermediary hosts. The endoparasite Bracon sp. is a parasite of the weevil Neoglocianus (Ceutorrhynchus) maculaalba (macula-alba) living in poppy heads. The species Baryscapus (Tetrastichus) diaphantus (terminalis) is a parasite of Bracon. All three are, therefore, members of a catena around the weevil, but the last one also appears in the catena linked to Eurybia cardui that lives in the flowerhead of Centaurea sadleriana and, moreover, also in the catena connected to the oak gall wasp Biorrhiza pallida. We know from our own studies that the adult B. diaphantus that is linked to the poppy head weevil appears in the middle of summer, while those active in the catenae around Eurybia cardui and Biorrhiza pallida emerge in spring. It is likely that this population could not insert itself into the catena around the poppy head weevil if the overwintering generation did not have the two other catenae at their disposal nearby. Examining the role of constituent populations in a catena, we can distinguish two sharply different groups. It is obvious that we need to distinguish between the larval populations of Cydia pomonella, its parasite, Perilampus laevifrons, and its hyperparasite Dibrachys microgastri (cavus) and the great tit, for example. One or two semaphoronts of the latter may visit the orchard, and among other prey, may consume the pupae of the codling moth (with its parasite) and fly away, perhaps even the same day, not to be seen for several days. A different one would be a goshawk catching the tit, or a cat preying on its distant nest. Likewise, the larval populations of Syrphus, Aphidius, Pachyneuron spp. active in a colony of aphids must be considered differently from the Coccinella septempunctata adult that stays there for 1-2 hours, destroying a few aphids, and then moves to feed on scale insect nymphs on the next tree. This is not a matter of mono- or polyphagy, which would be an idiobiological and coenological view. The above mentioned larval populations of Perilampus and Dibrachys, or the Syrphus, Aphidius and Pachyneuron are permanent residents around the codling moth- or aphidbased catenae, while the other animals are not. Therefore, all catenae have a core, that stays together for longer time scales, and cannot remove itself, and there are elements that are transients, temporarily contacting the core catena, but soon cutting their links to it. This casts a sharp light onto the dynamics of the zoocoenosis: the composition (and, also its species composition) can change from day to day, and even from hour to hour. An overabundant Agrotis segetum infestation will have a rich larval population, and numerous obstant elements, parasitic flies and wasps, and episitic beetles will also be present. This catena can remain unchanged for a week, when a murmuration of starlings arrives, and for a few hours, will feed on the larvae of the moth. There is no doubt that, during these hours, the starlings will belong to the catena; yet they were not until they physically appeared, and will not belong there on the next day when they have flown
