Quality of Sterile Male Tsetse after Long Distance Transport as Chilled, Irradiated Pupae

Abstract

BackgroundTsetse flies transmit trypanosomes that cause human and African animal trypanosomosis, a debilitating disease of humans (sleeping sickness) and livestock (nagana). An area-wide integrated pest management campaign against Glossina palpalis gambiensis has been implemented in Senegal since 2010 that includes a sterile insect technique (SIT) component. The SIT can only be successful when the sterile males that are destined for release have a flight ability, survival and competitiveness that are as close as possible to that of their wild male counterparts.Methodology/Principal FindingsTests were developed to assess the quality of G. p. gambiensis males that emerged from pupae that were produced and irradiated in Burkina Faso and Slovakia (irradiation done in Seibersdorf, Austria) and transported weekly under chilled conditions to Dakar, Senegal. For each consignment a sample of 50 pupae was used for a quality control test (QC group). To assess flight ability, the pupae were put in a cylinder filtering emerged flies that were able to escape the cylinder. The survival of these flyers was thereafter monitored under stress conditions (without feeding). Remaining pupae were emerged and released in the target area of the eradication programme (RF group). The following parameter values were obtained for the QC flies: average emergence rate more than 69%, median survival of 6 days, and average flight ability of more than 35%. The quality protocol was a good proxy of fly quality, explaining a large part of the variances of the examined parameters.Conclusions/SignificanceThe quality protocol described here will allow the accurate monitoring of the quality of shipped sterile male tsetse used in operational eradication programmes in the framework of the Pan-African Tsetse and Trypanosomosis Eradication Campaign.

Chilling, irradiation and transport of male Glossina palpalis gambiensis pupae: effect on the emergence, flight ability and survival.

“…After irradiation, pupae were packed and transported to Dakar as described in Pagabeleguem et al and Seck et al [14,18]. Briefly, irradiated pupae were placed in Petri dishes and packed in insulated boxes containing phase change material packs (S8, PCM Products Limited, Cambridgeshire, U. K.) to maintain the temperature between 10 ± 2°C.…”

“…The objective of the quality control is to evaluate the quality of sterile males, measured by the percentage of operational flies corresponding to the percentage of flies escaping the flight device [14]. Here, these quality control parameters were used to measure the impact of various treatments (chilling, irradiation, transport) on the emergence rate and rate of operational flies.…”

“…The Petri dish was then put in a flight cylinder, i.e. PVC tube 10 cm high and 8.4 cm in diameter [14]. The inner wall of the cylinder was coated with unscented talcum powder to prevent the flies from crawling out.…”

“…Preliminary observations already showed that the flight ability of sterile male G. p. gambiensis sent to the ISRA insectary was low compared to flies emerged at CIRDES and SAS insectaries [14], and this was related to the chilling and irradiation treatments and the transport of the sterile pupae before they reached the ISRA insectary. This is of prime importance as the quality of the released sterile males remains one of the most crucial prerequisites for the success of AW-IPM programs that have an SIT component.…”

“…Based on the quality protocol described in Seck et al [14], three biological parameters were measured to assess the impact of chilling, irradiation and transport on the quality of sterile males sent to Dakar for the eradication project in the Niayes area: i) adult emergence, ii) flight ability, and iii) survival of the flyers under starvation.…”