A Mark-Release-Recapture Study to Estimate Field Performance of Imported Radio-Sterilized Male Aedes albopictus in Albania

Abstract

The pathogen transmitting Aedes albopictus mosquito is spreading rapidly in Europe, putting millions of humans and animals at risk. This species is well-established in Albania since its first detection in 1979. The sterile insect technique (SIT) is increasingly gaining momentum worldwide as a component of area-wide-integrated pest management. However, estimating how the sterile males will perform in the field and the size of target populations is crucial for better decision-making, designing and elaborating appropriate SIT pilot trials, and subsequent large-scale release strategies. A mark-release-recapture (MRR) experiment was carried out in Albania within a highly urbanized area in the city of Tirana. The radio-sterilized adults of Ae. albopictus Albania strain males were transported by plane from Centro Agricoltura Ambiente (CAA) mass-production facility (Bologna, Italy), where they were reared. In Albania, sterile males were sugar-fed, marked with fluorescent powder, and released. The aim of this study was to estimate, under field conditions, their dispersal capacity, probability of daily survival and competitiveness, and the size of the target population. In addition, two adult mosquito collection methods were also evaluated: BG-Sentinel traps baited with BG-Lure and CO_2, (BGS) versus human landing catch (HLC). The overall recapture rates did not differ significantly between the two methods (2.36% and 1.57% of the total male released were recaptured respectively by BGS and HLC), suggesting a similar trapping efficiency under these conditions. Sterile males traveled a mean distance of 93.85 ± 42.58 m and dispersed up to 258 m. Moreover, they were observed living in the field up to 15 days after release with an average life expectancy of 4.26 ± 0.80 days. Whether mosquitoes were marked with green, blue, yellow, or pink, released at 3.00 p.m. or 6.00 p.m., there was no significant difference in the recapture, dispersal, and survival rates in the field. The Fried competitiveness index was estimated at 0.28. This mark-release-recapture study provided important data for better decision-making and planning before moving to pilot SIT trials in Albania. Moreover, it also showed that both BG-traps and HLC were successful in monitoring adult mosquitoes and provided similar estimations of the main entomological parameters needed.

Keywords: BG sentinel trap; Sterile Insect Technique; competitiveness; dispersal; management; mosquitoes; pest; survival.

FIGURE1

Map of mark release recapture setup in Tirana and distribution of 40 trapping stations for mosquito collection (two stations per hectare). (A) Location of release and control sites. (B) Study area is divided into sectors for simultaneous monitoring by different teams (green lines). The red stars represent the control sites, 700, 3,040, and 3,440 m from the release site. (C) Positions and number of trapping stations. Concentric red lines represent five annuli at 50, 100, 150, 200, and 250 m from the release point (red point in the center).

FIGURE 2

Capture of dusted-marked sterile males, wild male and female (both unmarked) mosquitoes as a function of time (September and October 2017) elapsed since release using BG-Sentinel trap and human landing catch. The regression line shows the trend of increase/decrease.

FIGURE 3

Distribution of accumulated recaptured sterile males in different collection stations (Figure 3A) and dispersal pattern as a function of distance from the release point (Figure 3B). The black dot in Figure 4A represents the release point, while the size of the dots corresponds to the number of marked mosquitoes caught at each site.

FIGURE 4

Dynamic of the sterile-to-wild male ratio over the distance from the release point (A) and time elapsed since release (B). Vertical dotted lines represent the release dates.

FIGURE 5

Estimation of the Fried index from 1,000 bootstraps in the distributions of sterile to wild male ratios in traps. The density corresponds to the percentage of the simulations for a given value.