Automated 3D-image based tracking system
A high-speed stereovision camera (G3 Evo 3, TYZX®) was fixed on the top of a beehive (10-frame Dadant type) to track the flights of bees and hornets at the beehive entrance (Figure 1a ). A controller laptop was used to schedule the recordings and to encode the raw RGB-D videos before being dumped on a NAS (Network Attached Storage). Video surveillance was deemed as a robust and effective method to measure the exact number of honey bees at the entrance of the colony. The experimental beehive was located nearby the town of La Rochelle (France) (46°8’N, 1°8’W), 200 km from where the Asian hornet was first spotted in 2004 (Haxaire et al., 2006; Villemant et al., 2011). The video surveillance was carried out from October 16th to October 25th 2015. In this oceanic climate, the ambient temperature ranged between 6°C and 17°C, wind speed ranged between 11km.h-1 and 39km.h-1, and the relative humidity ranged between 65 and 82%. Video tracking was performed from 9am to 6pm over 10 consecutive days, providing a total of 90 hours of recorded activity, corresponding to more than a terabyte of compressed data (i.e. RGB-D videos above 50 fps). The monitored beehive was isolated in the apiary (i.e. no other beehives in a 300m radius) in order to ensure that all observed trajectories belonged to the target hive. The stereovision camera was placed 50 cm above the flight board of the beehive to ensure the non-trivial trade-off between the device intrusiveness (no nearby source of disturbance), the image definition (at least 8 pixels per bee on the flight board) and the observed volume (that must include the 50 cm wide flight board). The Western honey bees (Apis mellifera ) were not bred from any particular genetic strain, while the native populations are Apis mellifera melliefra in the region (Requier et al., 2019b) with common hybridization towards A. mellifera mellifera ×caucasica (Requier et al., 2017). The Asian hornet is present in high abundance in the region since 15 years (Rome and Villemant, 2022).