The probable function of abdominal contractions and liquid drops during the emergence of Zygoptera and Anisoptera (Odonata)

Abstract

The transition between larval and adult stage in amphibious insects is called emergence. During emergence abdominal contractions and excretion of liquid drops can be observed in several insect orders. Since the function of these processes is not yet known in odonates, this study examines the probable function of abdominal contractions and excretion of liquid drops in Zygoptera and Anisoptera. By subdividing the emergence into 12 successive stages and counting abdominal contractions as well as the excreted liquid drops during these stages we set up a systematic data collection. In all investigated individuals, both processes began in the middle of the entire emergence. We found that abdominal contractions occurred more frequently at the beginning of the latter half of emergence. The number of excreted liquid drops, however, was higher in the end, shortly before the maiden flight. Concerning the number of excreted liquid drops, we found a significant difference between Zygoptera and Anisoptera. Our findings suggest that there might be a relationship between the two processes, probably explainable by the hemolymph circulation as seen in Lepidoptera. However, abdominal contractions and liquid drops seemed to be crucial for the emergence of Zygoptera and Anisoptera.

Keywords: Odonata, Anisoptera, Zygoptera, dragonfly, damselfly, emergence, hemolymph, hemolymph circulation, abdominal contractions, liquid drops

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