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Keywords:

  • Ceratitis capitata ;
  • flight ability;
  • ground release machine;
  • physical damage;
  • sterile insect technique;
  • survival

Abstract

A prototype of an improved automated ground release machine was assessed and found, with further improvements, to have the potential to be a promising tool for the release of quality sterile Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) flies in small- and medium-scale SIT control programmes. The following quality parameters of sterile flies were assessed: (i) flight ability, (ii) physical damage caused by the ground release machine, (iii) survival under stress conditions without food and water and (iv) water condensation on flies, after 0.5 and 2 h under the automatically controlled abiotic conditions of 16 ± 0.8°C and ∼58% relative humidity. A total number of seven different treatments, five involving flies held inside the ground release machine and two control treatments of chilled and non-chilled flies not held inside the ground release machine, were evaluated to assess sterile male quality. Flight ability was as high as 97% in the control treatment (no ground release), compared with the lowest value of 92.5% when a 1-m-long screw-auger, as part of the ground release machine, was tested. Use of a 1-m-long screw-auger significantly increased the percentage of damaged flies up to 7.2%, compared with ≤1.7% in the control treatments. It is confirmed that the length of the screw-auger is the most important factor affecting quality of the released flies in the ground release system tested. Also, interaction of duration of time inside the machine, screw-auger rotation and the effect of the directional discharge blower significantly increases the percentage of damaged flies. Evaluation of sterile fly survival under stress conditions, without food and water, confirms that movement or handling of the flies inside the ground release machine drastically decreases percentage of live insects from ≤ 4.5% after 24 h and 0.0% after 48 h, compared with 18.67–21.67% after 24 h and 3.50–5.83% after 48 h in the control treatments. The most important factors affecting sterile fly quality, such as condensation, compaction and damage, from moving mechanical parts are demonstrated to be minimized or eliminated by making adaptations to the ground release machine construction.