The influence of sterilisation on sound production in the tsetse fly, Glossina pallidipes

The Sterile Insect Technique is applied for the area-wide control of insect pests as a target-specific method. Therefore large numbers of male tsetse flies are reared and sterilised by irradiating them with gamma rays. Irradiation is normally carried out in air, but in an attempt to reduce somatic damage irradiation may be carried out in nitrogen. Fertile and sterilised male tsetse flies, Glossina pallidipes, were investigated in regard to their acoustic behaviour. Sounds produced by the tsetse flies are a means of communication and play an important role in physiological activities of feeding, mating and larvi-position. For the first time, this study will show possible differences in the pattern of sound production of fertile and sterile male Glossina pallidipes taking into consideration the two methods of irradiation. Sound production by three groups of flies (fertile, sterilised in air and sterilised in nitrogen) was studied under laboratory conditions at the University of Vienna. The Entomology Unit, FAO/IAEA Agriculture and Biotechnology Laboratory, Seibersdorf, provided newly emerged and fed tsetse flies. Recordings of spontaneous sound activity and measurements of the sound pressure level were carried out on the first three days. The recorded sounds were analysed with the software STX considering the temporal pattern of the sounds and the frequency parameters. A typical sonagram of the sounds produced by a male tsetse fly is seen in a Figure, showing the periodic nature of the frequencies. The frequencies and the sound pressure level of the sounds will be compared between the fertile and sterile flies. These parameters will provide a measure of the relative fitness of sterile and fertile flies. A comparison of the flies sterilised in air and in nitrogen will demonstrate whether one of the treatments is less harmful for the insects. It is expected that irradiation in nitrogen will cause less damage to the flies, because of the reduced number of free radicals that are produced during irradiation. Investigations on this technique, which is not yet fully developed, should be intensified if sound proves to give a useful measure of fitness. The duration of the sounds shows a high range of variation, which suggests that a system of coded signals exist, as has been proposed by Kolbe. It is supposed, that the signals are not produced at random, but are formed upon a recognizable pattern. It remains unclear, in which way the information is encoded. These analyses will give further information about the underlying mechanisms of the acoustic behaviour of the tsetse fly Glossina pallidipes with the attempt to improve the Sterile Insect Technique