Standardization of the FAO/IAEA Flight Test for Quality Control of Sterile Mosquitoes

Abstract

Successful implementation of the sterile insect technique (SIT) against Aedes aegypti and Aedes albopictus relies on maintaining a consistent release of high-quality sterile males. Affordable, rapid, practical quality control tools based on the male’s flight ability (ability to escape from a flight device) may contribute to meeting this requirement. Therefore, this study aims to standardize the use of the original FAO/IAEA rapid quality control flight test device (FTD) (version 1.0), while improving handling conditions and reducing the device’s overall cost by assessing factors that could impact the subsequent flight ability of Aedes mosquitoes. The new FTD (version 1.1) is easier to use. The most important factors affecting escape rates were found to be tube color (or “shade”), the combined use of a lure and fan, mosquito species, and mosquito age and density (25; 50; 75; 100 males). Other factors measured but found to be less important were the duration of the test (30, 60, 90, 120 min), fan speed (normal 3000 rpm vs. high 6000 rpm), and mosquito strain origin. In addition, a cheaper version of the FTD (version 2.0) that holds eight individual tubes instead of 40 was designed and successfully validated against the new FTD (version 1.1). It was sensitive enough to distinguish between the effects of cold stress and high irradiation dose. Therefore, the eight-tube FTD may be used to assess Aedes’ flight ability. This study demonstrated that the new designs (versions 1.1 and 2.0) of the FTD could be used for standard routine quality assessments of Aedes mosquitoes required for an SIT and other male release-based programs.

Exploring Conditions for Handling Packing and Shipping Aedes aegypti Males to Support an SIT Field Project in Brazil

“…From all evaluated parameters for chilling, we found that the escape rate (provided by the flight ability test) was more sensitive than survival and immediate mortality to detect a potential impact after 60 min at 4 °C. The escape rate was pointed out as an excellent quality control parameter since it is sensitive to distinguish differences among species, ages, and stress levels (i.e., irradiation, chilling, compaction), which reflects directly the male quality [ 39 , 58 ]. During an operational program is essential to have quicker tools to provide data to help managers make timely decisions.…”

“…Finally, compaction did not affect the full insemination rate; this result contrasts with the study of Culbert et al (2018) [ 41 ]. We also have to consider the role of different strains, species, insect age, and methodological performance in this response, as was recently pointed out by Maïga et al (2022) [ 58 ].…”

Radiation dose-fractionation in adult Aedes aegypti mosquitoes

“…To avoid prolonging the male production duration in an SIT facility, no more than 2 fractionated doses were considered for this study. Nor were recovery periods of more than 2 days considered between exposures, as it has been recommended to release the sterile males at around day 4 or 5 at the peak of their flight and mating activity, after which the flight ability begins to decline [ 29 ]. One and 2 days were selected as intervals also to ensure that there was sufficient time for the males to recover not only from the effects of the first irradiation, but also from the stress of handling before and during exposures, as it has been shown that, for example, flight ability is restored when males are given 1–2 days of rest post-exposure [ 29 ].…”

“…There was no difference observed in flight ability between males subjected to acute or fractioned doses. All treatment groups performed equally as compared to non-irradiated control groups, except treatment group F. This result suggests that subjection to one high dose, or the double handling, or only having one recovery day is tolerable in terms of flight ability; however, when all three factors are combined, this reduces the overall male quality, which is reflected by the reduced escape rates [ 29 ]. Although not statistically significant, the trend was that the double handled males all had the lowest recorded escape rates (C–F), when compared to the low scores of the males handled only once (A and B), suggesting that stress from handling can be more detrimental than irradiation itself [ 9 ].…”

“…(Note: As the flight test requires that all treatment groups and control are run at the same time, and with adults of the same age, sample groups B, C and E had 2 recovery days after the last irradiation exposure and prior to the flight test, whereas groups D and F only had 1 day of rest). The flight test was performed as described in [ 29 ]. Two biological repetitions with each two technical repeats were performed for each treatment group and control.…”