Datensatz

Zusammenfassung

The influence of the internal water balance on the phototactic behaviour in the walking female fly (Calliphora erythrocephala Meig.) was investigated. The phototactic reaction depends on the age of the flies and the duration of water withdrawal. In young blowflies with progressive dehydration, the strength of the light reaction varies considerably from fly to fly. From the 4th. day of life onwards up to day 21 the flies respond much more homogeneously and elicit a reproduceable temporal pattern of reaction (Figs. 2 and 3). All the following statements refer to the behaviour of 10-day-old, virgin females, which, under optimal humidity conditions, have been shown to be spontancously photonegative (Meyer, 1978). The phototactic reaction of progressively dehydrated flies depends in a characteristic manner on the illumination conditions during the intervals between tests. If the flies are kept in darkness during these intervals, the light reaction varies rhythmically, with a period of almost exactly 12 h (Figs. 4a and 5). Under the test conditions this rhythm is found not to vary with the time of day (Fig.4a), or with the length of the between-test intervals, for intervals up to 4h long (Fig. 6). If the flies are kept under illumination during the intervals between tests, the light reaction becomes arhythmical. After an initial maximum after 2–4h of dehydration, further photopositive responses are severely suppressed (Fig. 4b). When the ocelli are covered, the between-test illumination no longer influences the mean response to light. The arhythmic dehydrationtime vs. light-reaction curve in this case is characterised by a strong sustained enhancement of runs towards the light after 10h of dehydration (Fig. 7). A preliminary model of a possible control system for this moisture-dependent phototactic switching is presented, from which all essential results can be deduced. This system determines the phototactic turning direction from the ocelli afferences. These afferences act upon the central nervous system in two ways: directly and also indirectly via the internal water regulation.